# `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.