ast — Abstract syntax trees¶

Root nodes¶

class ast.Module(body, type_ignores)¶

A Python module, as with file input. Node type generated by ast.parse() in the default "exec" mode.

body is a list of the module’s Statements.

type_ignores is a list of the module’s type ignore comments; see ast.parse() for more details.

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

class ast.Expression(body)¶

A single Python expression input. Node type generated by ast.parse() when mode is "eval".

body is a single node, one of the expression types.

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

class ast.Interactive(body)¶

A single interactive input, like in Interactive Mode. Node type generated by ast.parse() when mode is "single".

body is a list of statement nodes.

>>> print(ast.dump(ast.parse('x = 1; y = 2', mode='single'), indent=4))
Interactive(
    body=[
        Assign(
            targets=[
                Name(id='x', ctx=Store())],
            value=Constant(value=1)),
        Assign(
            targets=[
                Name(id='y', ctx=Store())],
            value=Constant(value=2))])

class ast.FunctionType(argtypes, returns)¶

A representation of an old-style type comments for functions, as Python versions prior to 3.5 didn’t support PEP 484 annotations. Node type generated by ast.parse() when mode is "func_type".

Such type comments would look like this:

def sum_two_number(a, b):
    # type: (int, int) -> int
    return a + b

argtypes is a list of expression nodes.

returns is a single expression node.

>>> print(ast.dump(ast.parse('(int, str) -> List[int]', mode='func_type'), indent=4))
FunctionType(
    argtypes=[
        Name(id='int'),
        Name(id='str')],
    returns=Subscript(
        value=Name(id='List'),
        slice=Name(id='int')))

Added in version 3.8.

Literals¶

class ast.Constant(value, kind)¶

A constant value. The value attribute of the Constant literal contains the Python object it represents. The values represented can be instances of str, bytes, int, float, complex, and bool, and the constants None and Ellipsis.

The kind attribute is an optional string. For string literals with a u prefix, kind is set to 'u'. For all other constants, kind is None.

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

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

  • 97 (ord('a')): !a ASCII formatting

  • 114 (ord('r')): !r repr() formatting

  • 115 (ord('s')): !s string 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'),
                conversion=-1),
            Constant(value=') is '),
            FormattedValue(
                value=Call(
                    func=Name(id='sin'),
                    args=[
                        Name(id='a')]),
                conversion=-1,
                format_spec=JoinedStr(
                    values=[
                        Constant(value='.3')]))]))

class ast.TemplateStr(values, /)¶

Added in version 3.14.

Node representing a template string literal, comprising a series of Interpolation and Constant nodes. These nodes may be any order, and do not need to be interleaved.

>>> expr = ast.parse('t"{name} finished {place:ordinal}"', mode='eval')
>>> print(ast.dump(expr, indent=4))
Expression(
    body=TemplateStr(
        values=[
            Interpolation(
                value=Name(id='name'),
                str='name',
                conversion=-1),
            Constant(value=' finished '),
            Interpolation(
                value=Name(id='place'),
                str='place',
                conversion=-1,
                format_spec=JoinedStr(
                    values=[
                        Constant(value='ordinal')]))]))

class ast.Interpolation(value, str, conversion, format_spec=None)¶

Added in version 3.14.

Node representing a single interpolation field in a template string literal.

• value is any expression node (such as a literal, a variable, or a function call). This has the same meaning as FormattedValue.value.

• str is a constant containing the text of the interpolation expression.

  If str is set to None, then value is used to generate code when calling ast.unparse(). This no longer guarantees that the generated code is identical to the original and is intended for code generation.

• conversion is an integer:

  • -1: no conversion

  • 97 (ord('a')): !a ASCII conversion

  • 114 (ord('r')): !r repr() conversion

  • 115 (ord('s')): !s string conversion

  This has the same meaning as FormattedValue.conversion.

• 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. This has the same meaning as FormattedValue.format_spec.

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)]))
>>> 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)]))

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')]))

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'))])

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

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

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'))])

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')))])

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')))

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'),
        op=Add(),
        right=Name(id='y')))

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'),
            Name(id='y')]))

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'),
            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)¶

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.

The args and keywords arguments are optional and default to empty lists.

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

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'),
        body=Name(id='a'),
        orelse=Name(id='c')))

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'),
        attr='colour'))

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)))

Added in version 3.8.

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))])

>>> 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'))])

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

An assignment with a type annotation. target is a single node and can be a Name, an Attribute or a Subscript. annotation is the annotation, such as a Constant or Name node. value is a single optional node.

simple is always either 0 (indicating a “complex” target) or 1 (indicating a “simple” target). A “simple” target consists solely of a Name node that does not appear between parentheses; all other targets are considered complex. Only simple targets appear in the __annotations__ dictionary of modules and classes.

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

>>> 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'),
            value=Constant(value=1),
            simple=0)])

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

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

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 cannot 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))])

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'),
            cause=Name(id='y'))])

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'),
            msg=Name(id='y'))])

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())])])

class ast.Pass¶

A pass statement.

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

class ast.TypeAlias(name, type_params, value)¶

A type alias created through the type statement. name is the name of the alias, type_params is a list of type parameters, and value is the value of the type alias.

>>> print(ast.dump(ast.parse('type Alias = int'), indent=4))
Module(
    body=[
        TypeAlias(
            name=Name(id='Alias', ctx=Store()),
            value=Name(id='int'))])

Added in version 3.12.

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

Control flow¶

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'),
            body=[
                Expr(
                    value=Constant(value=Ellipsis))],
            orelse=[
                If(
                    test=Name(id='y'),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))],
                    orelse=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

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, List, Attribute or Subscript 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'),
            body=[
                Expr(
                    value=Constant(value=Ellipsis))],
            orelse=[
                Expr(
                    value=Constant(value=Ellipsis))])])

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'),
            body=[
                Expr(
                    value=Constant(value=Ellipsis))],
            orelse=[
                Expr(
                    value=Constant(value=Ellipsis))])])

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'),
            body=[
                If(
                    test=Compare(
                        left=Name(id='a'),
                        ops=[
                            Gt()],
                        comparators=[
                            Constant(value=5)]),
                    body=[
                        Break()],
                    orelse=[
                        Continue()])])])

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'),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                ExceptHandler(
                    type=Name(id='OtherException'),
                    name='e',
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])],
            orelse=[
                Expr(
                    value=Constant(value=Ellipsis))],
            finalbody=[
                Expr(
                    value=Constant(value=Ellipsis))])])

class ast.TryStar(body, handlers, orelse, finalbody)¶

try blocks which are followed by except* clauses. The attributes are the same as for Try but the ExceptHandler nodes in handlers are interpreted as except* blocks rather than except.

>>> print(ast.dump(ast.parse("""
... try:
...    ...
... except* Exception:
...    ...
... """), indent=4))
Module(
    body=[
        TryStar(
            body=[
                Expr(
                    value=Constant(value=Ellipsis))],
            handlers=[
                ExceptHandler(
                    type=Name(id='Exception'),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.11.

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'),
                        op=Add(),
                        right=Constant(value=1)))],
            handlers=[
                ExceptHandler(
                    type=Name(id='TypeError'),
                    body=[
                        Pass()])])])

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'),
                    optional_vars=Name(id='b', ctx=Store())),
                withitem(
                    context_expr=Name(id='c'),
                    optional_vars=Name(id='d', ctx=Store()))],
            body=[
                Expr(
                    value=Call(
                        func=Name(id='something'),
                        args=[
                            Name(id='b'),
                            Name(id='d')]))])])

Pattern matching¶

class ast.Match(subject, cases)¶

A match statement. subject holds the subject of the match (the object that is being matched against the cases) and cases contains an iterable of match_case nodes with the different cases.

Added in version 3.10.

class ast.match_case(pattern, guard, body)¶

A single case pattern in a match statement. pattern contains the match pattern that the subject will be matched against. Note that the AST nodes produced for patterns differ from those produced for expressions, even when they share the same syntax.

The guard attribute contains an expression that will be evaluated if the pattern matches the subject.

body contains a list of nodes to execute if the pattern matches and the result of evaluating the guard expression is true.

>>> print(ast.dump(ast.parse("""
... match x:
...     case [x] if x>0:
...         ...
...     case tuple():
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x'),
            cases=[
                match_case(
                    pattern=MatchSequence(
                        patterns=[
                            MatchAs(name='x')]),
                    guard=Compare(
                        left=Name(id='x'),
                        ops=[
                            Gt()],
                        comparators=[
                            Constant(value=0)]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchClass(
                        cls=Name(id='tuple')),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.10.

class ast.MatchValue(value)¶

A match literal or value pattern that compares by equality. value is an expression node. Permitted value nodes are restricted as described in the match statement documentation. This pattern succeeds if the match subject is equal to the evaluated value.

>>> print(ast.dump(ast.parse("""
... match x:
...     case "Relevant":
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x'),
            cases=[
                match_case(
                    pattern=MatchValue(
                        value=Constant(value='Relevant')),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.10.

class ast.MatchSingleton(value)¶

A match literal pattern that compares by identity. value is the singleton to be compared against: None, True, or False. This pattern succeeds if the match subject is the given constant.

>>> print(ast.dump(ast.parse("""
... match x:
...     case None:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x'),
            cases=[
                match_case(
                    pattern=MatchSingleton(value=None),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.10.

class ast.MatchSequence(patterns)¶

A match sequence pattern. patterns contains the patterns to be matched against the subject elements if the subject is a sequence. Matches a variable length sequence if one of the subpatterns is a MatchStar node, otherwise matches a fixed length sequence.

>>> print(ast.dump(ast.parse("""
... match x:
...     case [1, 2]:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x'),
            cases=[
                match_case(
                    pattern=MatchSequence(
                        patterns=[
                            MatchValue(
                                value=Constant(value=1)),
                            MatchValue(
                                value=Constant(value=2))]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.10.

class ast.MatchStar(name)¶

Matches the rest of the sequence in a variable length match sequence pattern. If name is not None, a list containing the remaining sequence elements is bound to that name if the overall sequence pattern is successful.

>>> print(ast.dump(ast.parse("""
... match x:
...     case [1, 2, *rest]:
...         ...
...     case [*_]:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x'),
            cases=[
                match_case(
                    pattern=MatchSequence(
                        patterns=[
                            MatchValue(
                                value=Constant(value=1)),
                            MatchValue(
                                value=Constant(value=2)),
                            MatchStar(name='rest')]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchSequence(
                        patterns=[
                            MatchStar()]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.10.

class ast.MatchMapping(keys, patterns, rest)¶

A match mapping pattern. keys is a sequence of expression nodes. patterns is a corresponding sequence of pattern nodes. rest is an optional name that can be specified to capture the remaining mapping elements. Permitted key expressions are restricted as described in the match statement documentation.

This pattern succeeds if the subject is a mapping, all evaluated key expressions are present in the mapping, and the value corresponding to each key matches the corresponding subpattern. If rest is not None, a dict containing the remaining mapping elements is bound to that name if the overall mapping pattern is successful.

>>> print(ast.dump(ast.parse("""
... match x:
...     case {1: _, 2: _}:
...         ...
...     case {**rest}:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x'),
            cases=[
                match_case(
                    pattern=MatchMapping(
                        keys=[
                            Constant(value=1),
                            Constant(value=2)],
                        patterns=[
                            MatchAs(),
                            MatchAs()]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchMapping(rest='rest'),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.10.

class ast.MatchClass(cls, patterns, kwd_attrs, kwd_patterns)¶

A match class pattern. cls is an expression giving the nominal class to be matched. patterns is a sequence of pattern nodes to be matched against the class defined sequence of pattern matching attributes. kwd_attrs is a sequence of additional attributes to be matched (specified as keyword arguments in the class pattern), kwd_patterns are the corresponding patterns (specified as keyword values in the class pattern).

This pattern succeeds if the subject is an instance of the nominated class, all positional patterns match the corresponding class-defined attributes, and any specified keyword attributes match their corresponding pattern.

Note: classes may define a property that returns self in order to match a pattern node against the instance being matched. Several builtin types are also matched that way, as described in the match statement documentation.

>>> print(ast.dump(ast.parse("""
... match x:
...     case Point2D(0, 0):
...         ...
...     case Point3D(x=0, y=0, z=0):
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x'),
            cases=[
                match_case(
                    pattern=MatchClass(
                        cls=Name(id='Point2D'),
                        patterns=[
                            MatchValue(
                                value=Constant(value=0)),
                            MatchValue(
                                value=Constant(value=0))]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchClass(
                        cls=Name(id='Point3D'),
                        kwd_attrs=[
                            'x',
                            'y',
                            'z'],
                        kwd_patterns=[
                            MatchValue(
                                value=Constant(value=0)),
                            MatchValue(
                                value=Constant(value=0)),
                            MatchValue(
                                value=Constant(value=0))]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.10.

class ast.MatchAs(pattern, name)¶

A match “as-pattern”, capture pattern or wildcard pattern. pattern contains the match pattern that the subject will be matched against. If the pattern is None, the node represents a capture pattern (i.e a bare name) and will always succeed.

The name attribute contains the name that will be bound if the pattern is successful. If name is None, pattern must also be None and the node represents the wildcard pattern.

>>> print(ast.dump(ast.parse("""
... match x:
...     case [x] as y:
...         ...
...     case _:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x'),
            cases=[
                match_case(
                    pattern=MatchAs(
                        pattern=MatchSequence(
                            patterns=[
                                MatchAs(name='x')]),
                        name='y'),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchAs(),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.10.

class ast.MatchOr(patterns)¶

A match “or-pattern”. An or-pattern matches each of its subpatterns in turn to the subject, until one succeeds. The or-pattern is then deemed to succeed. If none of the subpatterns succeed the or-pattern fails. The patterns attribute contains a list of match pattern nodes that will be matched against the subject.

>>> print(ast.dump(ast.parse("""
... match x:
...     case [x] | (y):
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x'),
            cases=[
                match_case(
                    pattern=MatchOr(
                        patterns=[
                            MatchSequence(
                                patterns=[
                                    MatchAs(name='x')]),
                            MatchAs(name='y')]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])])

Added in version 3.10.

Type annotations¶

class ast.TypeIgnore(lineno, tag)¶

A # type: ignore comment located at lineno. tag is the optional tag specified by the form # type: ignore <tag>.

>>> print(ast.dump(ast.parse('x = 1 # type: ignore', type_comments=True), indent=4))
Module(
    body=[
        Assign(
            targets=[
                Name(id='x', ctx=Store())],
            value=Constant(value=1))],
    type_ignores=[
        TypeIgnore(lineno=1, tag='')])
>>> print(ast.dump(ast.parse('x: bool = 1 # type: ignore[assignment]', type_comments=True), indent=4))
Module(
    body=[
        AnnAssign(
            target=Name(id='x', ctx=Store()),
            annotation=Name(id='bool'),
            value=Constant(value=1),
            simple=1)],
    type_ignores=[
        TypeIgnore(lineno=1, tag='[assignment]')])

Note

TypeIgnore nodes are not generated when the type_comments parameter is set to False (default). See ast.parse() for more details.

Added in version 3.8.

Type parameters¶

Type parameters can exist on classes, functions, and type aliases.

class ast.TypeVar(name, bound, default_value)¶

A typing.TypeVar. name is the name of the type variable. bound is the bound or constraints, if any. If bound is a Tuple, it represents constraints; otherwise it represents the bound. default_value is the default value; if the TypeVar has no default, this attribute will be set to None.

>>> print(ast.dump(ast.parse("type Alias[T: int = bool] = list[T]"), indent=4))
Module(
    body=[
        TypeAlias(
            name=Name(id='Alias', ctx=Store()),
            type_params=[
                TypeVar(
                    name='T',
                    bound=Name(id='int'),
                    default_value=Name(id='bool'))],
            value=Subscript(
                value=Name(id='list'),
                slice=Name(id='T')))])

Added in version 3.12.

Changed in version 3.13: Added the default_value parameter.

class ast.ParamSpec(name, default_value)¶

A typing.ParamSpec. name is the name of the parameter specification. default_value is the default value; if the ParamSpec has no default, this attribute will be set to None.

>>> print(ast.dump(ast.parse("type Alias[**P = [int, str]] = Callable[P, int]"), indent=4))
Module(
    body=[
        TypeAlias(
            name=Name(id='Alias', ctx=Store()),
            type_params=[
                ParamSpec(
                    name='P',
                    default_value=List(
                        elts=[
                            Name(id='int'),
                            Name(id='str')]))],
            value=Subscript(
                value=Name(id='Callable'),
                slice=Tuple(
                    elts=[
                        Name(id='P'),
                        Name(id='int')])))])

Added in version 3.12.

Changed in version 3.13: Added the default_value parameter.

class ast.TypeVarTuple(name, default_value)¶

A typing.TypeVarTuple. name is the name of the type variable tuple. default_value is the default value; if the TypeVarTuple has no default, this attribute will be set to None.

>>> print(ast.dump(ast.parse("type Alias[*Ts = ()] = tuple[*Ts]"), indent=4))
Module(
    body=[
        TypeAlias(
            name=Name(id='Alias', ctx=Store()),
            type_params=[
                TypeVarTuple(name='Ts', default_value=Tuple())],
            value=Subscript(
                value=Name(id='tuple'),
                slice=Tuple(
                    elts=[
                        Starred(
                            value=Name(id='Ts'))])))])

Added in version 3.12.

Changed in version 3.13: Added the default_value parameter.

Function and class definitions¶

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

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_params is a list of type parameters.

type_comment¶

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

Changed in version 3.12: Added type_params.

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(
                    args=[
                        arg(arg='x'),
                        arg(arg='y')]),
                body=Constant(value=Ellipsis)))])

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 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(
                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'),
                Name(id='decorator2')],
            returns=Constant(value='return annotation'))])

class ast.Return(value)¶

A return statement.

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

class ast.Yield(value)¶

class ast.YieldFrom(value)¶

A yield or yield from expression. Because these are expressions, they must be wrapped in an 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')))])

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

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'])])

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

class ast.ClassDef(name, bases, keywords, body, decorator_list, type_params)¶

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.

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

• decorator_list is a list of nodes, as in FunctionDef.

• type_params is a list of type parameters.

>>> 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'),
                Name(id='base2')],
            keywords=[
                keyword(
                    arg='metaclass',
                    value=Name(id='meta'))],
            body=[
                Pass()],
            decorator_list=[
                Name(id='decorator1'),
                Name(id='decorator2')])])

Changed in version 3.12: Added type_params.

Async and await¶

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

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

Changed in version 3.12: Added type_params.

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(),
            body=[
                Expr(
                    value=Await(
                        value=Call(
                            func=Name(id='other_func'))))])])

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.