"ast" --- Árboles de sintaxis abstracta
***************************************

**Código fuente:** Lib/ast.py

======================================================================

El módulo "ast" ayuda a las aplicaciones de Python a procesar árboles
de la gramática de sintaxis abstracta de Python. La sintaxis abstracta
en sí misma puede cambiar con cada versión de Python; Este módulo
ayuda a descubrir mediante programación cómo se ve la gramática
actual.

Se puede generar un árbol de sintaxis abstracta pasando
"ast.PyCF_ONLY_AST" como un indicador de la función incorporada
"compile()", o usando el ayudante "parse()" provisto en este módulo.
El resultado será un árbol de objetos cuyas clases todas heredan de
"ast.AST". Se puede compilar un árbol de sintaxis abstracta en un
objeto de código Python utilizando la función incorporada "compile()".


Gramática abstracta
===================

La gramática abstracta se define actualmente de la siguiente manera:

   -- ASDL's 4 builtin types are:
   -- identifier, int, string, constant

   module Python
   {
       mod = Module(stmt* body, type_ignore* type_ignores)
           | Interactive(stmt* body)
           | Expression(expr body)
           | FunctionType(expr* argtypes, expr returns)

       stmt = FunctionDef(identifier name, arguments args,
                          stmt* body, expr* decorator_list, expr? returns,
                          string? type_comment)
             | AsyncFunctionDef(identifier name, arguments args,
                                stmt* body, expr* decorator_list, expr? returns,
                                string? type_comment)

             | ClassDef(identifier name,
                expr* bases,
                keyword* keywords,
                stmt* body,
                expr* decorator_list)
             | Return(expr? value)

             | Delete(expr* targets)
             | Assign(expr* targets, expr value, string? type_comment)
             | AugAssign(expr target, operator op, expr value)
             -- 'simple' indicates that we annotate simple name without parens
             | AnnAssign(expr target, expr annotation, expr? value, int simple)

             -- use 'orelse' because else is a keyword in target languages
             | For(expr target, expr iter, stmt* body, stmt* orelse, string? type_comment)
             | AsyncFor(expr target, expr iter, stmt* body, stmt* orelse, string? type_comment)
             | While(expr test, stmt* body, stmt* orelse)
             | If(expr test, stmt* body, stmt* orelse)
             | With(withitem* items, stmt* body, string? type_comment)
             | AsyncWith(withitem* items, stmt* body, string? type_comment)

             | Raise(expr? exc, expr? cause)
             | Try(stmt* body, excepthandler* handlers, stmt* orelse, stmt* finalbody)
             | Assert(expr test, expr? msg)

             | Import(alias* names)
             | ImportFrom(identifier? module, alias* names, int? level)

             | Global(identifier* names)
             | Nonlocal(identifier* names)
             | Expr(expr value)
             | Pass | Break | Continue

             -- col_offset is the byte offset in the utf8 string the parser uses
             attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

             -- BoolOp() can use left & right?
       expr = BoolOp(boolop op, expr* values)
            | NamedExpr(expr target, expr value)
            | BinOp(expr left, operator op, expr right)
            | UnaryOp(unaryop op, expr operand)
            | Lambda(arguments args, expr body)
            | IfExp(expr test, expr body, expr orelse)
            | Dict(expr* keys, expr* values)
            | Set(expr* elts)
            | ListComp(expr elt, comprehension* generators)
            | SetComp(expr elt, comprehension* generators)
            | DictComp(expr key, expr value, comprehension* generators)
            | GeneratorExp(expr elt, comprehension* generators)
            -- the grammar constrains where yield expressions can occur
            | Await(expr value)
            | Yield(expr? value)
            | YieldFrom(expr value)
            -- need sequences for compare to distinguish between
            -- x < 4 < 3 and (x < 4) < 3
            | Compare(expr left, cmpop* ops, expr* comparators)
            | Call(expr func, expr* args, keyword* keywords)
            | FormattedValue(expr value, int? conversion, expr? format_spec)
            | JoinedStr(expr* values)
            | Constant(constant value, string? kind)

            -- the following expression can appear in assignment context
            | Attribute(expr value, identifier attr, expr_context ctx)
            | Subscript(expr value, expr slice, expr_context ctx)
            | Starred(expr value, expr_context ctx)
            | Name(identifier id, expr_context ctx)
            | List(expr* elts, expr_context ctx)
            | Tuple(expr* elts, expr_context ctx)

            -- can appear only in Subscript
            | Slice(expr? lower, expr? upper, expr? step)

             -- col_offset is the byte offset in the utf8 string the parser uses
             attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

       expr_context = Load | Store | Del

       boolop = And | Or

       operator = Add | Sub | Mult | MatMult | Div | Mod | Pow | LShift
                    | RShift | BitOr | BitXor | BitAnd | FloorDiv

       unaryop = Invert | Not | UAdd | USub

       cmpop = Eq | NotEq | Lt | LtE | Gt | GtE | Is | IsNot | In | NotIn

       comprehension = (expr target, expr iter, expr* ifs, int is_async)

       excepthandler = ExceptHandler(expr? type, identifier? name, stmt* body)
                       attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

       arguments = (arg* posonlyargs, arg* args, arg? vararg, arg* kwonlyargs,
                    expr* kw_defaults, arg? kwarg, expr* defaults)

       arg = (identifier arg, expr? annotation, string? type_comment)
              attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

       -- keyword arguments supplied to call (NULL identifier for **kwargs)
       keyword = (identifier? arg, expr value)
                  attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

       -- import name with optional 'as' alias.
       alias = (identifier name, identifier? asname)

       withitem = (expr context_expr, expr? optional_vars)

       type_ignore = TypeIgnore(int lineno, string tag)
   }


Clases Nodo
===========

class ast.AST

   Esta es la base de todas las clases de nodo AST. Las clases de nodo
   reales se derivan del archivo "Parser/Python.asdl", que se
   reproduce abajo. Se definen en el módulo "_ast" C y se reexportan
   en "ast".

   Hay una clase definida para cada símbolo del lado izquierdo en la
   gramática abstracta (por ejemplo, "ast.stmt" o "ast.expr"). Además,
   hay una clase definida para cada constructor en el lado derecho;
   estas clases heredan de las clases para los árboles del lado
   izquierdo. Por ejemplo, "ast.BinOp" hereda de "ast.expr". Para las
   reglas de producción con alternativas (también conocidas como
   "sumas"), la clase del lado izquierdo es abstracta: solo se crean
   instancias de nodos de constructor específicos.

   _fields

      Cada clase concreta tiene un atributo "_fields" que proporciona
      los nombres de todos los nodos secundarios.

      Cada instancia de una clase concreta tiene un atributo para cada
      nodo secundario, del tipo definido en la gramática. Por ejemplo,
      las instancias "ast.BinOp" tienen un atributo "left" de tipo
      "ast.expr".

      Si estos atributos están marcados como opcionales en la
      gramática (usando un signo de interrogación), el valor podría
      ser "None". Si los atributos pueden tener cero o más valores
      (marcados con un asterisco), los valores se representan como
      listas de Python. Todos los atributos posibles deben estar
      presentes y tener valores válidos al compilar un AST con
      "compile()".

   lineno
   col_offset
   end_lineno
   end_col_offset

      Instances of "ast.expr" and "ast.stmt" subclasses have "lineno",
      "col_offset", "end_lineno", and "end_col_offset" attributes.
      The "lineno" and "end_lineno" are the first and last line
      numbers of the source text span (1-indexed so the first line is
      line 1), and the "col_offset" and "end_col_offset" are the
      corresponding UTF-8 byte offsets of the first and last tokens
      that generated the node. The UTF-8 offset is recorded because
      the parser uses UTF-8 internally.

      Tenga en cuenta que el compilador no requiere las posiciones
      finales y, por lo tanto, son opcionales. El desplazamiento final
      es *después* del último símbolo, por ejemplo, uno puede obtener
      el segmento fuente de un nodo de expresión de una línea usando
      "source_line[node.col_offset: node.end_col_offset]".

   El constructor de una clase "ast.T" analiza sus argumentos de la
   siguiente manera:

   * Si hay argumentos posicionales, debe haber tantos como elementos
     en "T._fields"; serán asignados como atributos de estos nombres.

   * Si hay argumentos de palabras clave, establecerán los atributos
     de los mismos nombres a los valores dados.

   Por ejemplo, para crear y completar un nodo "ast.UnaryOp", puede
   usar

      node = ast.UnaryOp()
      node.op = ast.USub()
      node.operand = ast.Constant()
      node.operand.value = 5
      node.operand.lineno = 0
      node.operand.col_offset = 0
      node.lineno = 0
      node.col_offset = 0

   o la más compacta

      node = ast.UnaryOp(ast.USub(), ast.Constant(5, lineno=0, col_offset=0),
                         lineno=0, col_offset=0)

Distinto en la versión 3.8: La clase "ast.Constant" ahora se usa para
todas las constantes.

Distinto en la versión 3.9: Simple indices are represented by their
value, extended slices are represented as tuples.

Obsoleto desde la versión 3.8: Old classes "ast.Num", "ast.Str",
"ast.Bytes", "ast.NameConstant" and "ast.Ellipsis" are still
available, but they will be removed in future Python releases.  In the
meantime, instantiating them will return an instance of a different
class.

Obsoleto desde la versión 3.9: Old classes "ast.Index" and
"ast.ExtSlice" are still available, but they will be removed in future
Python releases. In the meantime, instantiating them will return an
instance of a different class.

Nota:

  The descriptions of the specific node classes displayed here were
  initially adapted from the fantastic Green Tree Snakes project and
  all its contributors.


Literals
--------

class ast.Constant(value)

   A constant value. The "value" attribute of the "Constant" literal
   contains the Python object it represents. The values represented
   can be simple types such as a number, string or "None", but also
   immutable container types (tuples and frozensets) if all of their
   elements are constant.

      >>> print(ast.dump(ast.parse('123', mode='eval'), indent=4))
      Expression(
          body=Constant(value=123))

class ast.FormattedValue(value, conversion, format_spec)

   Node representing a single formatting field in an f-string. If the
   string contains a single formatting field and nothing else the node
   can be isolated otherwise it appears in "JoinedStr".

   * "value" is any expression node (such as a literal, a variable, or
     a function call).

   * "conversion" is an integer:

     * -1: no formatting

     * 115: "!s" string formatting

     * 114: "!r" repr formatting

     * 97: "!a" ascii formatting

   * "format_spec" is a "JoinedStr" node representing the formatting
     of the value, or "None" if no format was specified. Both
     "conversion" and "format_spec" can be set at the same time.

class ast.JoinedStr(values)

   An f-string, comprising a series of "FormattedValue" and "Constant"
   nodes.

      >>> print(ast.dump(ast.parse('f"sin({a}) is {sin(a):.3}"', mode='eval'), indent=4))
      Expression(
          body=JoinedStr(
              values=[
                  Constant(value='sin('),
                  FormattedValue(
                      value=Name(id='a', ctx=Load()),
                      conversion=-1),
                  Constant(value=') is '),
                  FormattedValue(
                      value=Call(
                          func=Name(id='sin', ctx=Load()),
                          args=[
                              Name(id='a', ctx=Load())],
                          keywords=[]),
                      conversion=-1,
                      format_spec=JoinedStr(
                          values=[
                              Constant(value='.3')]))]))

class ast.List(elts, ctx)
class ast.Tuple(elts, ctx)

   A list or tuple. "elts" holds a list of nodes representing the
   elements. "ctx" is "Store" if the container is an assignment target
   (i.e. "(x,y)=something"), and "Load" otherwise.

      >>> print(ast.dump(ast.parse('[1, 2, 3]', mode='eval'), indent=4))
      Expression(
          body=List(
              elts=[
                  Constant(value=1),
                  Constant(value=2),
                  Constant(value=3)],
              ctx=Load()))
      >>> print(ast.dump(ast.parse('(1, 2, 3)', mode='eval'), indent=4))
      Expression(
          body=Tuple(
              elts=[
                  Constant(value=1),
                  Constant(value=2),
                  Constant(value=3)],
              ctx=Load()))

class ast.Set(elts)

   A set. "elts" holds a list of nodes representing the set's
   elements.

      >>> print(ast.dump(ast.parse('{1, 2, 3}', mode='eval'), indent=4))
      Expression(
          body=Set(
              elts=[
                  Constant(value=1),
                  Constant(value=2),
                  Constant(value=3)]))

class ast.Dict(keys, values)

   A dictionary. "keys" and "values" hold lists of nodes representing
   the keys and the values respectively, in matching order (what would
   be returned when calling "dictionary.keys()" and
   "dictionary.values()").

   When doing dictionary unpacking using dictionary literals the
   expression to be expanded goes in the "values" list, with a "None"
   at the corresponding position in "keys".

      >>> print(ast.dump(ast.parse('{"a":1, **d}', mode='eval'), indent=4))
      Expression(
          body=Dict(
              keys=[
                  Constant(value='a'),
                  None],
              values=[
                  Constant(value=1),
                  Name(id='d', ctx=Load())]))


Variables
---------

class ast.Name(id, ctx)

   A variable name. "id" holds the name as a string, and "ctx" is one
   of the following types.

class ast.Load
class ast.Store
class ast.Del

   Variable references can be used to load the value of a variable, to
   assign a new value to it, or to delete it. Variable references are
   given a context to distinguish these cases.

      >>> print(ast.dump(ast.parse('a'), indent=4))
      Module(
          body=[
              Expr(
                  value=Name(id='a', ctx=Load()))],
          type_ignores=[])

      >>> print(ast.dump(ast.parse('a = 1'), indent=4))
      Module(
          body=[
              Assign(
                  targets=[
                      Name(id='a', ctx=Store())],
                  value=Constant(value=1))],
          type_ignores=[])

      >>> print(ast.dump(ast.parse('del a'), indent=4))
      Module(
          body=[
              Delete(
                  targets=[
                      Name(id='a', ctx=Del())])],
          type_ignores=[])

class ast.Starred(value, ctx)

   A "*var" variable reference. "value" holds the variable, typically
   a "Name" node. This type must be used when building a "Call" node
   with "*args".

      >>> print(ast.dump(ast.parse('a, *b = it'), indent=4))
      Module(
          body=[
              Assign(
                  targets=[
                      Tuple(
                          elts=[
                              Name(id='a', ctx=Store()),
                              Starred(
                                  value=Name(id='b', ctx=Store()),
                                  ctx=Store())],
                          ctx=Store())],
                  value=Name(id='it', ctx=Load()))],
          type_ignores=[])


Expressions
-----------

class ast.Expr(value)

   When an expression, such as a function call, appears as a statement
   by itself with its return value not used or stored, it is wrapped
   in this container. "value" holds one of the other nodes in this
   section, a "Constant", a "Name", a "Lambda", a "Yield" or
   "YieldFrom" node.

      >>> print(ast.dump(ast.parse('-a'), indent=4))
      Module(
          body=[
              Expr(
                  value=UnaryOp(
                      op=USub(),
                      operand=Name(id='a', ctx=Load())))],
          type_ignores=[])

class ast.UnaryOp(op, operand)

   A unary operation. "op" is the operator, and "operand" any
   expression node.

class ast.UAdd
class ast.USub
class ast.Not
class ast.Invert

   Unary operator tokens. "Not" is the "not" keyword, "Invert" is the
   "~" operator.

      >>> print(ast.dump(ast.parse('not x', mode='eval'), indent=4))
      Expression(
          body=UnaryOp(
              op=Not(),
              operand=Name(id='x', ctx=Load())))

class ast.BinOp(left, op, right)

   A binary operation (like addition or division). "op" is the
   operator, and "left" and "right" are any expression nodes.

      >>> print(ast.dump(ast.parse('x + y', mode='eval'), indent=4))
      Expression(
          body=BinOp(
              left=Name(id='x', ctx=Load()),
              op=Add(),
              right=Name(id='y', ctx=Load())))

class ast.Add
class ast.Sub
class ast.Mult
class ast.Div
class ast.FloorDiv
class ast.Mod
class ast.Pow
class ast.LShift
class ast.RShift
class ast.BitOr
class ast.BitXor
class ast.BitAnd
class ast.MatMult

   Binary operator tokens.

class ast.BoolOp(op, values)

   A boolean operation, 'or' or 'and'. "op" is "Or" or "And". "values"
   are the values involved. Consecutive operations with the same
   operator, such as "a or b or c", are collapsed into one node with
   several values.

   This doesn't include "not", which is a "UnaryOp".

      >>> print(ast.dump(ast.parse('x or y', mode='eval'), indent=4))
      Expression(
          body=BoolOp(
              op=Or(),
              values=[
                  Name(id='x', ctx=Load()),
                  Name(id='y', ctx=Load())]))

class ast.And
class ast.Or

   Boolean operator tokens.

class ast.Compare(left, ops, comparators)

   A comparison of two or more values. "left" is the first value in
   the comparison, "ops" the list of operators, and "comparators" the
   list of values after the first element in the comparison.

      >>> print(ast.dump(ast.parse('1 <= a < 10', mode='eval'), indent=4))
      Expression(
          body=Compare(
              left=Constant(value=1),
              ops=[
                  LtE(),
                  Lt()],
              comparators=[
                  Name(id='a', ctx=Load()),
                  Constant(value=10)]))

class ast.Eq
class ast.NotEq
class ast.Lt
class ast.LtE
class ast.Gt
class ast.GtE
class ast.Is
class ast.IsNot
class ast.In
class ast.NotIn

   Comparison operator tokens.

class ast.Call(func, args, keywords, starargs, kwargs)

   A function call. "func" is the function, which will often be a
   "Name" or "Attribute" object. Of the arguments:

   * "args" holds a list of the arguments passed by position.

   * "keywords" holds a list of "keyword" objects representing
     arguments passed by keyword.

   When creating a "Call" node, "args" and "keywords" are required,
   but they can be empty lists. "starargs" and "kwargs" are optional.

      >>> print(ast.dump(ast.parse('func(a, b=c, *d, **e)', mode='eval'), indent=4))
      Expression(
          body=Call(
              func=Name(id='func', ctx=Load()),
              args=[
                  Name(id='a', ctx=Load()),
                  Starred(
                      value=Name(id='d', ctx=Load()),
                      ctx=Load())],
              keywords=[
                  keyword(
                      arg='b',
                      value=Name(id='c', ctx=Load())),
                  keyword(
                      value=Name(id='e', ctx=Load()))]))

class ast.keyword(arg, value)

   A keyword argument to a function call or class definition. "arg" is
   a raw string of the parameter name, "value" is a node to pass in.

class ast.IfExp(test, body, orelse)

   An expression such as "a if b else c". Each field holds a single
   node, so in the following example, all three are "Name" nodes.

      >>> print(ast.dump(ast.parse('a if b else c', mode='eval'), indent=4))
      Expression(
          body=IfExp(
              test=Name(id='b', ctx=Load()),
              body=Name(id='a', ctx=Load()),
              orelse=Name(id='c', ctx=Load())))

class ast.Attribute(value, attr, ctx)

   Attribute access, e.g. "d.keys". "value" is a node, typically a
   "Name". "attr" is a bare string giving the name of the attribute,
   and "ctx" is "Load", "Store" or "Del" according to how the
   attribute is acted on.

      >>> print(ast.dump(ast.parse('snake.colour', mode='eval'), indent=4))
      Expression(
          body=Attribute(
              value=Name(id='snake', ctx=Load()),
              attr='colour',
              ctx=Load()))

class ast.NamedExpr(target, value)

      A named expression. This AST node is produced by the assignment
      expressions operator (also known as the walrus operator). As
      opposed to the "Assign" node in which the first argument can be
      multiple nodes, in this case both "target" and "value" must be
      single nodes.

      >>> print(ast.dump(ast.parse('(x := 4)', mode='eval'), indent=4))
      Expression(
          body=NamedExpr(
              target=Name(id='x', ctx=Store()),
              value=Constant(value=4)))


Subscripting
~~~~~~~~~~~~

class ast.Subscript(value, slice, ctx)

   A subscript, such as "l[1]". "value" is the subscripted object
   (usually sequence or mapping). "slice" is an index, slice or key.
   It can be a "Tuple" and contain a "Slice". "ctx" is "Load", "Store"
   or "Del" according to the action performed with the subscript.

      >>> print(ast.dump(ast.parse('l[1:2, 3]', mode='eval'), indent=4))
      Expression(
          body=Subscript(
              value=Name(id='l', ctx=Load()),
              slice=Tuple(
                  elts=[
                      Slice(
                          lower=Constant(value=1),
                          upper=Constant(value=2)),
                      Constant(value=3)],
                  ctx=Load()),
              ctx=Load()))

class ast.Slice(lower, upper, step)

   Regular slicing (on the form "lower:upper" or "lower:upper:step").
   Can occur only inside the *slice* field of "Subscript", either
   directly or as an element of "Tuple".

      >>> print(ast.dump(ast.parse('l[1:2]', mode='eval'), indent=4))
      Expression(
          body=Subscript(
              value=Name(id='l', ctx=Load()),
              slice=Slice(
                  lower=Constant(value=1),
                  upper=Constant(value=2)),
              ctx=Load()))


Comprehensions
~~~~~~~~~~~~~~

class ast.ListComp(elt, generators)
class ast.SetComp(elt, generators)
class ast.GeneratorExp(elt, generators)
class ast.DictComp(key, value, generators)

   List and set comprehensions, generator expressions, and dictionary
   comprehensions. "elt" (or "key" and "value") is a single node
   representing the part that will be evaluated for each item.

   "generators" is a list of "comprehension" nodes.

      >>> print(ast.dump(ast.parse('[x for x in numbers]', mode='eval'), indent=4))
      Expression(
          body=ListComp(
              elt=Name(id='x', ctx=Load()),
              generators=[
                  comprehension(
                      target=Name(id='x', ctx=Store()),
                      iter=Name(id='numbers', ctx=Load()),
                      ifs=[],
                      is_async=0)]))
      >>> print(ast.dump(ast.parse('{x: x**2 for x in numbers}', mode='eval'), indent=4))
      Expression(
          body=DictComp(
              key=Name(id='x', ctx=Load()),
              value=BinOp(
                  left=Name(id='x', ctx=Load()),
                  op=Pow(),
                  right=Constant(value=2)),
              generators=[
                  comprehension(
                      target=Name(id='x', ctx=Store()),
                      iter=Name(id='numbers', ctx=Load()),
                      ifs=[],
                      is_async=0)]))
      >>> print(ast.dump(ast.parse('{x for x in numbers}', mode='eval'), indent=4))
      Expression(
          body=SetComp(
              elt=Name(id='x', ctx=Load()),
              generators=[
                  comprehension(
                      target=Name(id='x', ctx=Store()),
                      iter=Name(id='numbers', ctx=Load()),
                      ifs=[],
                      is_async=0)]))

class ast.comprehension(target, iter, ifs, is_async)

   One "for" clause in a comprehension. "target" is the reference to
   use for each element - typically a "Name" or "Tuple" node. "iter"
   is the object to iterate over. "ifs" is a list of test expressions:
   each "for" clause can have multiple "ifs".

   "is_async" indicates a comprehension is asynchronous (using an
   "async for" instead of "for"). The value is an integer (0 or 1).

      >>> print(ast.dump(ast.parse('[ord(c) for line in file for c in line]', mode='eval'),
      ...                indent=4)) # Multiple comprehensions in one.
      Expression(
          body=ListComp(
              elt=Call(
                  func=Name(id='ord', ctx=Load()),
                  args=[
                      Name(id='c', ctx=Load())],
                  keywords=[]),
              generators=[
                  comprehension(
                      target=Name(id='line', ctx=Store()),
                      iter=Name(id='file', ctx=Load()),
                      ifs=[],
                      is_async=0),
                  comprehension(
                      target=Name(id='c', ctx=Store()),
                      iter=Name(id='line', ctx=Load()),
                      ifs=[],
                      is_async=0)]))

      >>> print(ast.dump(ast.parse('(n**2 for n in it if n>5 if n<10)', mode='eval'),
      ...                indent=4)) # generator comprehension
      Expression(
          body=GeneratorExp(
              elt=BinOp(
                  left=Name(id='n', ctx=Load()),
                  op=Pow(),
                  right=Constant(value=2)),
              generators=[
                  comprehension(
                      target=Name(id='n', ctx=Store()),
                      iter=Name(id='it', ctx=Load()),
                      ifs=[
                          Compare(
                              left=Name(id='n', ctx=Load()),
                              ops=[
                                  Gt()],
                              comparators=[
                                  Constant(value=5)]),
                          Compare(
                              left=Name(id='n', ctx=Load()),
                              ops=[
                                  Lt()],
                              comparators=[
                                  Constant(value=10)])],
                      is_async=0)]))

      >>> print(ast.dump(ast.parse('[i async for i in soc]', mode='eval'),
      ...                indent=4)) # Async comprehension
      Expression(
          body=ListComp(
              elt=Name(id='i', ctx=Load()),
              generators=[
                  comprehension(
                      target=Name(id='i', ctx=Store()),
                      iter=Name(id='soc', ctx=Load()),
                      ifs=[],
                      is_async=1)]))


Statements
----------

class ast.Assign(targets, value, type_comment)

   An assignment. "targets" is a list of nodes, and "value" is a
   single node.

   Multiple nodes in "targets" represents assigning the same value to
   each. Unpacking is represented by putting a "Tuple" or "List"
   within "targets".

   type_comment

      "type_comment" is an optional string with the type annotation as
      a comment.

      >>> print(ast.dump(ast.parse('a = b = 1'), indent=4)) # Multiple assignment
      Module(
          body=[
              Assign(
                  targets=[
                      Name(id='a', ctx=Store()),
                      Name(id='b', ctx=Store())],
                  value=Constant(value=1))],
          type_ignores=[])

      >>> print(ast.dump(ast.parse('a,b = c'), indent=4)) # Unpacking
      Module(
          body=[
              Assign(
                  targets=[
                      Tuple(
                          elts=[
                              Name(id='a', ctx=Store()),
                              Name(id='b', ctx=Store())],
                          ctx=Store())],
                  value=Name(id='c', ctx=Load()))],
          type_ignores=[])

class ast.AnnAssign(target, annotation, value, simple)

   An assignment with a type annotation. "target" is a single node and
   can be a "Name", a "Attribute" or a "Subscript". "annotation" is
   the annotation, such as a "Constant" or "Name" node. "value" is a
   single optional node. "simple" is a boolean integer set to True for
   a "Name" node in "target" that do not appear in between parenthesis
   and are hence pure names and not expressions.

      >>> print(ast.dump(ast.parse('c: int'), indent=4))
      Module(
          body=[
              AnnAssign(
                  target=Name(id='c', ctx=Store()),
                  annotation=Name(id='int', ctx=Load()),
                  simple=1)],
          type_ignores=[])

      >>> print(ast.dump(ast.parse('(a): int = 1'), indent=4)) # Annotation with parenthesis
      Module(
          body=[
              AnnAssign(
                  target=Name(id='a', ctx=Store()),
                  annotation=Name(id='int', ctx=Load()),
                  value=Constant(value=1),
                  simple=0)],
          type_ignores=[])

      >>> print(ast.dump(ast.parse('a.b: int'), indent=4)) # Attribute annotation
      Module(
          body=[
              AnnAssign(
                  target=Attribute(
                      value=Name(id='a', ctx=Load()),
                      attr='b',
                      ctx=Store()),
                  annotation=Name(id='int', ctx=Load()),
                  simple=0)],
          type_ignores=[])

      >>> print(ast.dump(ast.parse('a[1]: int'), indent=4)) # Subscript annotation
      Module(
          body=[
              AnnAssign(
                  target=Subscript(
                      value=Name(id='a', ctx=Load()),
                      slice=Constant(value=1),
                      ctx=Store()),
                  annotation=Name(id='int', ctx=Load()),
                  simple=0)],
          type_ignores=[])

class ast.AugAssign(target, op, value)

   Augmented assignment, such as "a += 1". In the following example,
   "target" is a "Name" node for "x" (with the "Store" context), "op"
   is "Add", and "value" is a "Constant" with value for 1.

   The "target" attribute connot be of class "Tuple" or "List", unlike
   the targets of "Assign".

      >>> print(ast.dump(ast.parse('x += 2'), indent=4))
      Module(
          body=[
              AugAssign(
                  target=Name(id='x', ctx=Store()),
                  op=Add(),
                  value=Constant(value=2))],
          type_ignores=[])

class ast.Raise(exc, cause)

   A "raise" statement. "exc" is the exception object to be raised,
   normally a "Call" or "Name", or "None" for a standalone "raise".
   "cause" is the optional part for "y" in "raise x from y".

      >>> print(ast.dump(ast.parse('raise x from y'), indent=4))
      Module(
          body=[
              Raise(
                  exc=Name(id='x', ctx=Load()),
                  cause=Name(id='y', ctx=Load()))],
          type_ignores=[])

class ast.Assert(test, msg)

   An assertion. "test" holds the condition, such as a "Compare" node.
   "msg" holds the failure message.

      >>> print(ast.dump(ast.parse('assert x,y'), indent=4))
      Module(
          body=[
              Assert(
                  test=Name(id='x', ctx=Load()),
                  msg=Name(id='y', ctx=Load()))],
          type_ignores=[])

class ast.Delete(targets)

   Represents a "del" statement. "targets" is a list of nodes, such as
   "Name", "Attribute" or "Subscript" nodes.

      >>> print(ast.dump(ast.parse('del x,y,z'), indent=4))
      Module(
          body=[
              Delete(
                  targets=[
                      Name(id='x', ctx=Del()),
                      Name(id='y', ctx=Del()),
                      Name(id='z', ctx=Del())])],
          type_ignores=[])

class ast.Pass

   A "pass" statement.

      >>> print(ast.dump(ast.parse('pass'), indent=4))
      Module(
          body=[
              Pass()],
          type_ignores=[])

Other statements which are only applicable inside functions or loops
are described in other sections.


Imports
~~~~~~~

class ast.Import(names)

   An import statement. "names" is a list of "alias" nodes.

      >>> print(ast.dump(ast.parse('import x,y,z'), indent=4))
      Module(
          body=[
              Import(
                  names=[
                      alias(name='x'),
                      alias(name='y'),
                      alias(name='z')])],
          type_ignores=[])

class ast.ImportFrom(module, names, level)

   Represents "from x import y". "module" is a raw string of the
   'from' name, without any leading dots, or "None" for statements
   such as "from . import foo". "level" is an integer holding the
   level of the relative import (0 means absolute import).

      >>> print(ast.dump(ast.parse('from y import x,y,z'), indent=4))
      Module(
          body=[
              ImportFrom(
                  module='y',
                  names=[
                      alias(name='x'),
                      alias(name='y'),
                      alias(name='z')],
                  level=0)],
          type_ignores=[])

class ast.alias(name, asname)

   Both parameters are raw strings of the names. "asname" can be
   "None" if the regular name is to be used.

      >>> print(ast.dump(ast.parse('from ..foo.bar import a as b, c'), indent=4))
      Module(
          body=[
              ImportFrom(
                  module='foo.bar',
                  names=[
                      alias(name='a', asname='b'),
                      alias(name='c')],
                  level=2)],
          type_ignores=[])


Control flow
------------

Nota:

  Optional clauses such as "else" are stored as an empty list if
  they're not present.

class ast.If(test, body, orelse)

   An "if" statement. "test" holds a single node, such as a "Compare"
   node. "body" and "orelse" each hold a list of nodes.

   "elif" clauses don't have a special representation in the AST, but
   rather appear as extra "If" nodes within the "orelse" section of
   the previous one.

      >>> print(ast.dump(ast.parse("""
      ... if x:
      ...    ...
      ... elif y:
      ...    ...
      ... else:
      ...    ...
      ... """), indent=4))
      Module(
          body=[
              If(
                  test=Name(id='x', ctx=Load()),
                  body=[
                      Expr(
                          value=Constant(value=Ellipsis))],
                  orelse=[
                      If(
                          test=Name(id='y', ctx=Load()),
                          body=[
                              Expr(
                                  value=Constant(value=Ellipsis))],
                          orelse=[
                              Expr(
                                  value=Constant(value=Ellipsis))])])],
          type_ignores=[])

class ast.For(target, iter, body, orelse, type_comment)

   A "for" loop. "target" holds the variable(s) the loop assigns to,
   as a single "Name", "Tuple" or "List" node. "iter" holds the item
   to be looped over, again as a single node. "body" and "orelse"
   contain lists of nodes to execute. Those in "orelse" are executed
   if the loop finishes normally, rather than via a "break" statement.

   type_comment

      "type_comment" is an optional string with the type annotation as
      a comment.

      >>> print(ast.dump(ast.parse("""
      ... for x in y:
      ...     ...
      ... else:
      ...     ...
      ... """), indent=4))
      Module(
          body=[
              For(
                  target=Name(id='x', ctx=Store()),
                  iter=Name(id='y', ctx=Load()),
                  body=[
                      Expr(
                          value=Constant(value=Ellipsis))],
                  orelse=[
                      Expr(
                          value=Constant(value=Ellipsis))])],
          type_ignores=[])

class ast.While(test, body, orelse)

   A "while" loop. "test" holds the condition, such as a "Compare"
   node.

      >> print(ast.dump(ast.parse("""
      ... while x:
      ...    ...
      ... else:
      ...    ...
      ... """), indent=4))
      Module(
          body=[
              While(
                  test=Name(id='x', ctx=Load()),
                  body=[
                      Expr(
                          value=Constant(value=Ellipsis))],
                  orelse=[
                      Expr(
                          value=Constant(value=Ellipsis))])],
          type_ignores=[])

class ast.Break
class ast.Continue

   The "break" and "continue" statements.

      >>> print(ast.dump(ast.parse("""\
      ... for a in b:
      ...     if a > 5:
      ...         break
      ...     else:
      ...         continue
      ...
      ... """), indent=4))
      Module(
          body=[
              For(
                  target=Name(id='a', ctx=Store()),
                  iter=Name(id='b', ctx=Load()),
                  body=[
                      If(
                          test=Compare(
                              left=Name(id='a', ctx=Load()),
                              ops=[
                                  Gt()],
                              comparators=[
                                  Constant(value=5)]),
                          body=[
                              Break()],
                          orelse=[
                              Continue()])],
                  orelse=[])],
          type_ignores=[])

class ast.Try(body, handlers, orelse, finalbody)

   "try" blocks. All attributes are list of nodes to execute, except
   for "handlers", which is a list of "ExceptHandler" nodes.

      >>> print(ast.dump(ast.parse("""
      ... try:
      ...    ...
      ... except Exception:
      ...    ...
      ... except OtherException as e:
      ...    ...
      ... else:
      ...    ...
      ... finally:
      ...    ...
      ... """), indent=4))
      Module(
          body=[
              Try(
                  body=[
                      Expr(
                          value=Constant(value=Ellipsis))],
                  handlers=[
                      ExceptHandler(
                          type=Name(id='Exception', ctx=Load()),
                          body=[
                              Expr(
                                  value=Constant(value=Ellipsis))]),
                      ExceptHandler(
                          type=Name(id='OtherException', ctx=Load()),
                          name='e',
                          body=[
                              Expr(
                                  value=Constant(value=Ellipsis))])],
                  orelse=[
                      Expr(
                          value=Constant(value=Ellipsis))],
                  finalbody=[
                      Expr(
                          value=Constant(value=Ellipsis))])],
          type_ignores=[])

class ast.ExceptHandler(type, name, body)

   A single "except" clause. "type" is the exception type it will
   match, typically a "Name" node (or "None" for a catch-all "except:"
   clause). "name" is a raw string for the name to hold the exception,
   or "None" if the clause doesn't have "as foo". "body" is a list of
   nodes.

      >>> print(ast.dump(ast.parse("""\
      ... try:
      ...     a + 1
      ... except TypeError:
      ...     pass
      ... """), indent=4))
      Module(
          body=[
              Try(
                  body=[
                      Expr(
                          value=BinOp(
                              left=Name(id='a', ctx=Load()),
                              op=Add(),
                              right=Constant(value=1)))],
                  handlers=[
                      ExceptHandler(
                          type=Name(id='TypeError', ctx=Load()),
                          body=[
                              Pass()])],
                  orelse=[],
                  finalbody=[])],
          type_ignores=[])

class ast.With(items, body, type_comment)

   A "with" block. "items" is a list of "withitem" nodes representing
   the context managers, and "body" is the indented block inside the
   context.

   type_comment

      "type_comment" is an optional string with the type annotation as
      a comment.

class ast.withitem(context_expr, optional_vars)

   A single context manager in a "with" block. "context_expr" is the
   context manager, often a "Call" node. "optional_vars" is a "Name",
   "Tuple" or "List" for the "as foo" part, or "None" if that isn't
   used.

      >>> print(ast.dump(ast.parse("""\
      ... with a as b, c as d:
      ...    something(b, d)
      ... """), indent=4))
      Module(
          body=[
              With(
                  items=[
                      withitem(
                          context_expr=Name(id='a', ctx=Load()),
                          optional_vars=Name(id='b', ctx=Store())),
                      withitem(
                          context_expr=Name(id='c', ctx=Load()),
                          optional_vars=Name(id='d', ctx=Store()))],
                  body=[
                      Expr(
                          value=Call(
                              func=Name(id='something', ctx=Load()),
                              args=[
                                  Name(id='b', ctx=Load()),
                                  Name(id='d', ctx=Load())],
                              keywords=[]))])],
          type_ignores=[])


Function and class definitions
------------------------------

class ast.FunctionDef(name, args, body, decorator_list, returns, type_comment)

   A function definition.

   * "name" is a raw string of the function name.

   * "args" is an "arguments" node.

   * "body" is the list of nodes inside the function.

   * "decorator_list" is the list of decorators to be applied, stored
     outermost first (i.e. the first in the list will be applied
     last).

   * "returns" is the return annotation.

   type_comment

      "type_comment" is an optional string with the type annotation as
      a comment.

class ast.Lambda(args, body)

   "lambda" is a minimal function definition that can be used inside
   an expression. Unlike "FunctionDef", "body" holds a single node.

      >>> print(ast.dump(ast.parse('lambda x,y: ...'), indent=4))
      Module(
          body=[
              Expr(
                  value=Lambda(
                      args=arguments(
                          posonlyargs=[],
                          args=[
                              arg(arg='x'),
                              arg(arg='y')],
                          kwonlyargs=[],
                          kw_defaults=[],
                          defaults=[]),
                      body=Constant(value=Ellipsis)))],
          type_ignores=[])

class ast.arguments(posonlyargs, args, vararg, kwonlyargs, kw_defaults, kwarg, defaults)

   The arguments for a function.

   * "posonlyargs", "args" and "kwonlyargs" are lists of "arg" nodes.

   * "vararg" and "kwarg" are single "arg" nodes, referring to the
     "*args, **kwargs" parameters.

   * "kw_defaults" is a list of default values for keyword-only
     arguments. If one is "None", the corresponding argument is
     required.

   * "defaults" is a list of default values for arguments that can be
     passed positionally. If there are fewer defaults, they correspond
     to the last n arguments.

class ast.arg(arg, annotation, type_comment)

   A single argument in a list. "arg" is a raw string of the argument
   name, "annotation" is its annotation, such as a "Str" or "Name"
   node.

   type_comment

      "type_comment" is an optional string with the type annotation as
      a comment

      >>> print(ast.dump(ast.parse("""\
      ... @decorator1
      ... @decorator2
      ... def f(a: 'annotation', b=1, c=2, *d, e, f=3, **g) -> 'return annotation':
      ...     pass
      ... """), indent=4))
      Module(
          body=[
              FunctionDef(
                  name='f',
                  args=arguments(
                      posonlyargs=[],
                      args=[
                          arg(
                              arg='a',
                              annotation=Constant(value='annotation')),
                          arg(arg='b'),
                          arg(arg='c')],
                      vararg=arg(arg='d'),
                      kwonlyargs=[
                          arg(arg='e'),
                          arg(arg='f')],
                      kw_defaults=[
                          None,
                          Constant(value=3)],
                      kwarg=arg(arg='g'),
                      defaults=[
                          Constant(value=1),
                          Constant(value=2)]),
                  body=[
                      Pass()],
                  decorator_list=[
                      Name(id='decorator1', ctx=Load()),
                      Name(id='decorator2', ctx=Load())],
                  returns=Constant(value='return annotation'))],
          type_ignores=[])

class ast.Return(value)

   A "return" statement.

      >>> print(ast.dump(ast.parse('return 4'), indent=4))
      Module(
          body=[
              Return(
                  value=Constant(value=4))],
          type_ignores=[])

class ast.Yield(value)
class ast.YieldFrom(value)

   A "yield" or "yield from" expression. Because these are
   expressions, they must be wrapped in a "Expr" node if the value
   sent back is not used.

      >>> print(ast.dump(ast.parse('yield x'), indent=4))
      Module(
          body=[
              Expr(
                  value=Yield(
                      value=Name(id='x', ctx=Load())))],
          type_ignores=[])

      >>> print(ast.dump(ast.parse('yield from x'), indent=4))
      Module(
          body=[
              Expr(
                  value=YieldFrom(
                      value=Name(id='x', ctx=Load())))],
          type_ignores=[])

class ast.Global(names)
class ast.Nonlocal(names)

   "global" and "nonlocal" statements. "names" is a list of raw
   strings.

      >>> print(ast.dump(ast.parse('global x,y,z'), indent=4))
      Module(
          body=[
              Global(
                  names=[
                      'x',
                      'y',
                      'z'])],
          type_ignores=[])

      >>> print(ast.dump(ast.parse('nonlocal x,y,z'), indent=4))
      Module(
          body=[
              Nonlocal(
                  names=[
                      'x',
                      'y',
                      'z'])],
          type_ignores=[])

class ast.ClassDef(name, bases, keywords, starargs, kwargs, body, decorator_list)

   A class definition.

   * "name" is a raw string for the class name

   * "bases" is a list of nodes for explicitly specified base classes.

   * "keywords" is a list of "keyword" nodes, principally for
     'metaclass'. Other keywords will be passed to the metaclass, as
     per PEP-3115.

   * "starargs" and "kwargs" are each a single node, as in a function
     call. starargs will be expanded to join the list of base classes,
     and kwargs will be passed to the metaclass.

   * "body" is a list of nodes representing the code within the class
     definition.

   * "decorator_list" is a list of nodes, as in "FunctionDef".

      >>> print(ast.dump(ast.parse("""\
      ... @decorator1
      ... @decorator2
      ... class Foo(base1, base2, metaclass=meta):
      ...     pass
      ... """), indent=4))
      Module(
          body=[
              ClassDef(
                  name='Foo',
                  bases=[
                      Name(id='base1', ctx=Load()),
                      Name(id='base2', ctx=Load())],
                  keywords=[
                      keyword(
                          arg='metaclass',
                          value=Name(id='meta', ctx=Load()))],
                  body=[
                      Pass()],
                  decorator_list=[
                      Name(id='decorator1', ctx=Load()),
                      Name(id='decorator2', ctx=Load())])],
          type_ignores=[])


Async and await
---------------

class ast.AsyncFunctionDef(name, args, body, decorator_list, returns, type_comment)

   An "async def" function definition. Has the same fields as
   "FunctionDef".

class ast.Await(value)

   An "await" expression. "value" is what it waits for. Only valid in
   the body of an "AsyncFunctionDef".

   >>> print(ast.dump(ast.parse("""\
   ... async def f():
   ...     await other_func()
   ... """), indent=4))
   Module(
       body=[
           AsyncFunctionDef(
               name='f',
               args=arguments(
                   posonlyargs=[],
                   args=[],
                   kwonlyargs=[],
                   kw_defaults=[],
                   defaults=[]),
               body=[
                   Expr(
                       value=Await(
                           value=Call(
                               func=Name(id='other_func', ctx=Load()),
                               args=[],
                               keywords=[])))],
               decorator_list=[])],
       type_ignores=[])

class ast.AsyncFor(target, iter, body, orelse, type_comment)
class ast.AsyncWith(items, body, type_comment)

   "async for" loops and "async with" context managers. They have the
   same fields as "For" and "With", respectively. Only valid in the
   body of an "AsyncFunctionDef".

Nota:

  When a string is parsed by "ast.parse()", operator nodes (subclasses
  of "ast.operator", "ast.unaryop", "ast.cmpop", "ast.boolop" and
  "ast.expr_context") on the returned tree will be singletons. Changes
  to one will be reflected in all other occurrences of the same value
  (e.g. "ast.Add").


Ayudantes de "ast"
==================

Además de las clases de nodo, el módulo "ast" define estas funciones y
clases de utilidad para atravesar árboles de sintaxis abstracta:

ast.parse(source, filename='<unknown>', mode='exec', *, type_comments=False, feature_version=None)

   Analiza la fuente en un nodo AST. Equivalente a "compile(source,
   filename, mode, ast.PyCF_ONLY_AST)".

   Si se proporciona "type_comments=True", el analizador se modifica
   para verificar y retornar los comentarios de tipo según lo
   especificado por **PEP 484** y **PEP 526**. Esto es equivalente a
   agregar "ast.PyCF_TYPE_COMMENTS" a los flags pasados a "compile()".
   Esto informará errores de sintaxis para comentarios de tipo fuera
   de lugar. Sin este flag, los comentarios de tipo se ignorarán y el
   campo "type_comment" en los nodos AST seleccionados siempre será
   "None". Además, las ubicaciones de los comentarios "# type: ignore"
   se retornarán como el atributo "type_ignores" de "Module" (de lo
   contrario, siempre es una lista vacía).

   Además, si "modo" es "'func_type'", la sintaxis de entrada se
   modifica para corresponder a **PEP 484** "comentarios de tipo de
   firma", por ejemplo "(str, int) -> List[str]".

   Además, establece "feature_version" en una tupla "(major, minor)"
   intentará analizar usando la gramática de esa versión de Python.
   Actualmente "major" debe ser igual a "3". Por ejemplo, establece
   "feature_version=(3, 4)" permitirá el uso de "async" y "await" como
   nombres de variables. La versión más baja admitida es "(3, 4)"; la
   más alto es "sys.version_info[0:2]".

   If source contains a null character ('0'), "ValueError" is raised.

      Advertencia:

        Note that successfully parsing source code into an AST object
        doesn't guarantee that the source code provided is valid
        Python code that can be executed as the compilation step can
        raise further "SyntaxError" exceptions. For instance, the
        source "return 42" generates a valid AST node for a return
        statement, but it cannot be compiled alone (it needs to be
        inside a function node).In particular, "ast.parse()" won't do
        any scoping checks, which the compilation step does.

   Advertencia:

     Es posible bloquear el intérprete de Python con una cadena de
     caracteres suficientemente grande/compleja debido a las
     limitaciones de profundidad de pila en el compilador AST de
     Python.

   Distinto en la versión 3.8: Se agregaron "type_comments",
   "mode='func_type'" y "feature_version".

ast.unparse(ast_obj)

   Unparse an "ast.AST" object and generate a string with code that
   would produce an equivalent "ast.AST" object if parsed back with
   "ast.parse()".

   Advertencia:

     The produced code string will not necessarily be equal to the
     original code that generated the "ast.AST" object (without any
     compiler optimizations, such as constant tuples/frozensets).

   Advertencia:

     Trying to unparse a highly complex expression would result with
     "RecursionError".

   Nuevo en la versión 3.9.

ast.literal_eval(node_or_string)

   Evaluate an expression node or a string containing only a Python
   literal or container display.  The string or node provided may only
   consist of the following Python literal structures: strings, bytes,
   numbers, tuples, lists, dicts, sets, booleans, and "None".

   This can be used for evaluating strings containing Python values
   without the need to parse the values oneself.  It is not capable of
   evaluating arbitrarily complex expressions, for example involving
   operators or indexing.

   This function had been documented as "safe" in the past without
   defining what that meant. That was misleading. This is specifically
   designed not to execute Python code, unlike the more general
   "eval()". There is no namespace, no name lookups, or ability to
   call out. But it is not free from attack: A relatively small input
   can lead to memory exhaustion or to C stack exhaustion, crashing
   the process. There is also the possibility for excessive CPU
   consumption denial of service on some inputs. Calling it on
   untrusted data is thus not recommended.

   Advertencia:

     It is possible to crash the Python interpreter due to stack depth
     limitations in Python's AST compiler.

   Distinto en la versión 3.2: Ahora permite bytes y establece
   literales.

   Distinto en la versión 3.9: Now supports creating empty sets with
   "'set()'".

ast.get_docstring(node, clean=True)

   Retorna la cadena de caracteres de documentación del *node* dado
   (que debe ser un nodo "FunctionDef", "AsyncFunctionDef",
   "ClassDef", o "Module"), o "None" si no tiene docstring. Si *clean*
   es verdadero, limpia la sangría del docstring con
   "inspect.cleandoc()".

   Distinto en la versión 3.5: "AsyncFunctionDef" ahora está
   soportada.

ast.get_source_segment(source, node, *, padded=False)

   Obtenga el segmento de código fuente del *source* que generó
   *node*. Si falta información de ubicación ("lineno", "end_lineno",
   "col_offset", o "end_col_offset"), retorna "None".

   Si *padded* es "True", la primera línea de una declaración de
   varias líneas se rellenará con espacios para que coincidan con su
   posición original.

   Nuevo en la versión 3.8.

ast.fix_missing_locations(node)

   Cuando compila un árbol de nodos con "compile()", el compilador
   espera los atributos "lineno" y "col_offset" para cada nodo que los
   soporta. Es bastante tedioso completar los nodos generados, por lo
   que este ayudante agrega estos atributos de forma recursiva donde
   aún no están establecidos, configurándolos en los valores del nodo
   principal. Funciona de forma recursiva comenzando en *node*.

ast.increment_lineno(node, n=1)

   Incremente el número de línea y el número de línea final de cada
   nodo en el árbol comenzando en *node* por *n*. Esto es útil para
   "mover código" a una ubicación diferente en un archivo.

ast.copy_location(new_node, old_node)

   Copia la ubicación de origen ("lineno", "col_offset", "end_lineno",
   y "end_col_offset") de *old_node* a *new_node* si es posible, y
   retorna *new_node*.

ast.iter_fields(node)

   Produce (*yield*) una tupla de "(fieldname, value)" para cada campo
   en "node._fields" que está presente en *node*.

ast.iter_child_nodes(node)

   Cede todos los nodos secundarios directos de *node*, es decir,
   todos los campos que son nodos y todos los elementos de campos que
   son listas de nodos.

ast.walk(node)

   Recursivamente produce todos los nodos descendientes en el árbol
   comenzando en *node* (incluido *node* en sí mismo), en ningún orden
   especificado. Esto es útil si solo desea modificar los nodos en su
   lugar y no le importa el contexto.

class ast.NodeVisitor

   Una clase base de visitante de nodo que recorre el árbol de
   sintaxis abstracta y llama a una función de visitante para cada
   nodo encontrado. Esta función puede retornar un valor que se
   reenvía mediante el método "visit()".

   Esta clase está destinada a ser subclase, con la subclase agregando
   métodos de visitante.

   visit(node)

      Visita un nodo. La implementación predeterminada llama al método
      llamado "self.visit_*classname*" donde *classname* es el nombre
      de la clase de nodo, o "generic_visit()" si ese método no
      existe.

   generic_visit(node)

      Este visitante llama "visit()" en todos los hijos del nodo.

      Tenga en cuenta que los nodos secundarios de los nodos que
      tienen un método de visitante personalizado no se visitarán a
      menos que el visitante llame "generic_visit()" o los visite a sí
      mismo.

   No use "NodeVisitor" si desea aplicar cambios a los nodos durante
   el recorrido. Para esto existe un visitante especial
   ("NodeTransformer") que permite modificaciones.

   Obsoleto desde la versión 3.8: Los métodos "visit_Num()",
   "visit_Str()", "visit_Bytes()", "visit_NameConstant()" y
   "visit_Ellipsis()" están en desuso ahora y no serán llamados en
   futuras versiones de Python. Agregue el método "visit_Constant()"
   para manejar todos los nodos constantes.

class ast.NodeTransformer

   Una subclase de "NodeVisitor" que recorre el árbol de sintaxis
   abstracta y permite la modificación de nodos.

   La clase "NodeTransformer" recorrerá el AST y usará el valor de
   retorno de los métodos del visitante para reemplazar o eliminar el
   nodo anterior. Si el valor de retorno del método de visitante es
   "None", el nodo se eliminará de su ubicación; de lo contrario, se
   reemplazará con el valor de retorno. El valor de retorno puede ser
   el nodo original, en cuyo caso no se realiza ningún reemplazo.

   Aquí hay un transformador de ejemplo que reescribe todas las
   apariciones de búsquedas de nombres ("foo") en "data['foo']":

      class RewriteName(NodeTransformer):

          def visit_Name(self, node):
              return Subscript(
                  value=Name(id='data', ctx=Load()),
                  slice=Constant(value=node.id),
                  ctx=node.ctx
              )

   Tenga en cuenta que si el nodo en el que está operando tiene nodos
   secundarios, debe transformar los nodos secundarios usted mismo o
   llamar primero al método "generic_visit()" para el nodo.

   Para los nodos que formaban parte de una colección de declaraciones
   (que se aplica a todos los nodos de declaración), el visitante
   también puede retornar una lista de nodos en lugar de solo un nodo.

   Si "NodeTransformer" introduce nuevos nodos (que no eran parte del
   árbol original) sin darles información de ubicación (como
   "lineno"), "fix_missing_locations()" debería llamarse con el nuevo
   sub-árbol para recalcular la información de ubicación

      tree = ast.parse('foo', mode='eval')
      new_tree = fix_missing_locations(RewriteName().visit(tree))

   Usualmente usas el transformador así:

      node = YourTransformer().visit(node)

ast.dump(node, annotate_fields=True, include_attributes=False, *, indent=None)

   Retorna un volcado formateado del árbol en *node*. Esto es
   principalmente útil para propósitos de depuración. Si
   *annotate_fields* es verdadero (por defecto), la cadena de
   caracteres retornada mostrará los nombres y los valores de los
   campos. Si *annotate_fields* es falso, la cadena de resultados será
   más compacta omitiendo nombres de campo no ambiguos. Los atributos
   como los números de línea y las compensaciones de columna no se
   vuelcan de forma predeterminada. Si esto se desea,
   *include_attributes* se puede establecer en verdadero.

   If *indent* is a non-negative integer or string, then the tree will
   be pretty-printed with that indent level.  An indent level of 0,
   negative, or """" will only insert newlines.  "None" (the default)
   selects the single line representation. Using a positive integer
   indent indents that many spaces per level.  If *indent* is a string
   (such as ""\t""), that string is used to indent each level.

   Distinto en la versión 3.9: Added the *indent* option.


Compiler Flags
==============

The following flags may be passed to "compile()" in order to change
effects on the compilation of a program:

ast.PyCF_ALLOW_TOP_LEVEL_AWAIT

   Enables support for top-level "await", "async for", "async with"
   and async comprehensions.

   Nuevo en la versión 3.8.

ast.PyCF_ONLY_AST

   Generates and returns an abstract syntax tree instead of returning
   a compiled code object.

ast.PyCF_TYPE_COMMENTS

   Enables support for **PEP 484** and **PEP 526** style type comments
   ("# type: <type>", "# type: ignore <stuff>").

   Nuevo en la versión 3.8.


Command-Line Usage
==================

Nuevo en la versión 3.9.

The "ast" module can be executed as a script from the command line. It
is as simple as:

   python -m ast [-m <mode>] [-a] [infile]

The following options are accepted:

-h, --help

   Show the help message and exit.

-m <mode>
--mode <mode>

   Specify what kind of code must be compiled, like the *mode*
   argument in "parse()".

--no-type-comments

   Don't parse type comments.

-a, --include-attributes

   Include attributes such as line numbers and column offsets.

-i <indent>
--indent <indent>

   Indentation of nodes in AST (number of spaces).

If "infile" is specified its contents are parsed to AST and dumped to
stdout.  Otherwise, the content is read from stdin.

Ver también:

  Green Tree Snakes, un recurso de documentación externo, tiene buenos
  detalles sobre cómo trabajar con Python AST.

  ASTTokens annotates Python ASTs with the positions of tokens and
  text in the source code that generated them. This is helpful for
  tools that make source code transformations.

  leoAst.py unifies the token-based and parse-tree-based views of
  python programs by inserting two-way links between tokens and ast
  nodes.

  LibCST parses code as a Concrete Syntax Tree that looks like an ast
  tree and keeps all formatting details. It's useful for building
  automated refactoring (codemod) applications and linters.

  Parso is a Python parser that supports error recovery and round-trip
  parsing for different Python versions (in multiple Python versions).
  Parso is also able to list multiple syntax errors in your python
  file.
