ast — Árboles de sintaxis abstracta

Código fuente: Lib/ast.py

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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.