ast --- 抽象構文木

ソースコード: Lib/ast.py


ast モジュールは、Python アプリケーションで Python の抽象構文木を処理しやすくするものです。抽象構文そのものは、Python のリリースごとに変化する可能性があります。このモジュールを使用すると、現在の文法をプログラム上で知る助けになるでしょう。

抽象構文木を作成するには、 ast.PyCF_ONLY_AST を組み込み関数 compile() のフラグとして渡すか、あるいはこのモジュールで提供されているヘルパー関数 parse() を使います。その結果は、 ast.AST を継承したクラスのオブジェクトのツリーとなります。抽象構文木は組み込み関数 compile() を使って Python コード・オブジェクトにコンパイルすることができます。

抽象文法 (Abstract Grammar)

抽象文法は、現在次のように定義されています:

-- 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)
}

Node クラス

class ast.AST

このクラスは全ての AST ノード・クラスの基底です。実際のノード・クラスは 後ほど 示す Parser/Python.asdl ファイルから派生したものです。これらのクラスは _ast C モジュールで定義され、 ast にもエクスポートし直されています。

抽象文法の左辺のシンボル一つずつにそれぞれ一つのクラスがあります (たとえば ast.stmtast.expr)。それに加えて、右辺のコンストラクタ一つずつにそれぞれ一つのクラスがあり、これらのクラスは左辺のツリーのクラスを継承しています。たとえば、 ast.BinOpast.expr から継承しています。代替を伴った生成規則 (production rules with alternatives) (別名 "sums") の場合、左辺は抽象クラスとなり、特定のコンストラクタ・ノードのインスタンスのみが作成されます。

_fields

各具象クラスは属性 _fields を持っており、すべての子ノードの名前をそこに保持しています。

具象クラスのインスタンスは、各子ノードに対してそれぞれひとつの属性を持っています。この属性は、文法で定義された型となります。たとえば ast.BinOp のインスタンスは left という属性を持っており、その型は ast.expr です。

これらの属性が、文法上 (クエスチョンマークを用いて) オプションであるとマークされている場合は、その値が None となることもあります。属性が0個以上の複数の値をとりうる場合 (アスタリスクでマークされている場合) は、値は Python のリストで表されます。全ての属性は AST を compile() でコンパイルする際には存在しなければならず、そして妥当な値でなければなりません。

lineno
col_offset
end_lineno
end_col_offset

Instances of ast.expr and ast.stmt subclasses have lineno, col_offset, lineno, and col_offset attributes. The lineno and end_lineno are the first and last line numbers of 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.

Note that the end positions are not required by the compiler and are therefore optional. The end offset is after the last symbol, for example one can get the source segment of a one-line expression node using source_line[node.col_offset : node.end_col_offset].

クラス ast.T のコンストラクタは引数を次のように解析します:

  • 位置引数があるとすれば、 T._fields にあるのと同じだけの個数が無ければなりません。これらの引数はそこにある名前を持った属性として割り当てられます。

  • キーワード引数があるとすれば、それらはその名前の属性にその値を割り当てられます。

たとえば、 ast.UnaryOp ノードを生成して属性を埋めるには、次のようにすることができます

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

もしくはよりコンパクトにも書けます

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

バージョン 3.8 で変更: ast.Constant が全ての定数に使われるようになりました。

バージョン 3.9 で変更: Simple indices are represented by their value, extended slices are represented as tuples.

バージョン 3.8 で非推奨: 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.

バージョン 3.9 で非推奨: 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.

リテラル

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=[])

式 (expression)

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

注釈

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 a 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.

注釈

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).

ast ヘルパー

ノード・クラスの他に、 ast モジュールは以下のような抽象構文木をトラバースするためのユーティリティ関数やクラスも定義しています:

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

source を解析して AST ノードにします。compile(source, filename, mode, ast.PyCF_ONLY_AST) と等価です。

If type_comments=True is given, the parser is modified to check and return type comments as specified by PEP 484 and PEP 526. This is equivalent to adding ast.PyCF_TYPE_COMMENTS to the flags passed to compile(). This will report syntax errors for misplaced type comments. Without this flag, type comments will be ignored, and the type_comment field on selected AST nodes will always be None. In addition, the locations of # type: ignore comments will be returned as the type_ignores attribute of Module (otherwise it is always an empty list).

In addition, if mode is 'func_type', the input syntax is modified to correspond to PEP 484 "signature type comments", e.g. (str, int) -> List[str].

Also, setting feature_version to a tuple (major, minor) will attempt to parse using that Python version's grammar. Currently major must equal to 3. For example, setting feature_version=(3, 4) will allow the use of async and await as variable names. The lowest supported version is (3, 4); the highest is sys.version_info[0:2].

警告

十分に大きい文字列や複雑な文字列によって Python の抽象構文木コンパイラのスタックの深さの限界を越えることで、 Python インタプリタをクラッシュさせることができます。

バージョン 3.8 で変更: type_commentsmode='func_type'``feature_version``が追加されました。

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().

警告

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).

警告

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

バージョン 3.9 で追加.

ast.literal_eval(node_or_string)

式ノードまたは Python のリテラルまたはコンテナのディスプレイ表現を表す文字列を安全に評価します。与えられる文字列またはノードは次のリテラルのみからなるものに限られます: 文字列、バイト列、数、タプル、リスト、辞書、集合、ブール値、 None

この関数は Python の式を含んだ信頼出来ない出どころからの文字列を、値自身を解析することなしに安全に評価するのに使えます。この関数は、例えば演算や添え字を含んだ任意の複雑な表現を評価するのには使えません。

警告

十分に大きい文字列や複雑な文字列によって Python の抽象構文木コンパイラのスタックの深さの限界を越えることで、 Python インタプリタをクラッシュさせることができます。

バージョン 3.2 で変更: バイト列リテラルと集合リテラルが受け取れるようになりました。

バージョン 3.9 で変更: Now supports creating empty sets with 'set()'.

ast.get_docstring(node, clean=True)

与えられた node (これは FunctionDef, AsyncFunctionDef, ClassDef, Module のいずれかのノードでなければなりません) のドキュメント文字列を返します。もしドキュメント文字列が無ければ None を返します。 clean が真ならば、ドキュメント文字列のインデントを inspect.cleandoc() を用いて一掃します。

バージョン 3.5 で変更: AsyncFunctionDef がサポートされました。

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

Get source code segment of the source that generated node. If some location information (lineno, end_lineno, col_offset, or end_col_offset) is missing, return None.

If padded is True, the first line of a multi-line statement will be padded with spaces to match its original position.

バージョン 3.8 で追加.

ast.fix_missing_locations(node)

compile() はノード・ツリーをコンパイルする際、 linenocol_offset 両属性をサポートする全てのノードに対しそれが存在するものと想定します。生成されたノードに対しこれらを埋めて回るのはどちらかというと退屈な作業なので、このヘルパーが再帰的に二つの属性がセットされていないものに親ノードと同じ値をセットしていきます。再帰の出発点が node です。

ast.increment_lineno(node, n=1)

Increment the line number and end line number of each node in the tree starting at node by n. This is useful to "move code" to a different location in a file.

ast.copy_location(new_node, old_node)

Copy source location (lineno, col_offset, end_lineno, and end_col_offset) from old_node to new_node if possible, and return new_node.

ast.iter_fields(node)

node にある node._fields のそれぞれのフィールドを (フィールド名, 値) のタプルとして yield します。

ast.iter_child_nodes(node)

node の直接の子ノード全てを yield します。すなわち、yield されるのは、ノードであるような全てのフィールドおよびノードのリストであるようなフィールドの全てのアイテムです。

ast.walk(node)

node の全ての子孫ノード(node 自体を含む)を再帰的に yield します。順番は決められていません。この関数はノードをその場で変更するだけで文脈を気にしないような場合に便利です。

class ast.NodeVisitor

抽象構文木を渡り歩いてビジター関数を見つけたノードごとに呼び出すノード・ビジターの基底クラスです。この関数は visit() メソッドに送られる値を返してもかまいません。

このクラスはビジター・メソッドを付け加えたサブクラスを派生させることを意図しています。

visit(node)

ノードを訪れます。デフォルトの実装では self.visit_classname というメソッド (ここで classname はノードのクラス名です) を呼び出すか、そのメソッドがなければ generic_visit() を呼び出します。

generic_visit(node)

このビジターはノードの全ての子について visit() を呼び出します。

注意して欲しいのは、専用のビジター・メソッドを具えたノードの子ノードは、このビジターが generic_visit() を呼び出すかそれ自身で子ノードを訪れない限り訪れられないということです。

トラバースの途中でノードを変化させたいならば NodeVisitor を使ってはいけません。そうした目的のために変更を許す特別なビジター (NodeTransformer) があります。

バージョン 3.8 で非推奨: Methods visit_Num(), visit_Str(), visit_Bytes(), visit_NameConstant() and visit_Ellipsis() are deprecated now and will not be called in future Python versions. Add the visit_Constant() method to handle all constant nodes.

class ast.NodeTransformer

NodeVisitor のサブクラスで抽象構文木を渡り歩きながらノードを変更することを許すものです。

NodeTransformer は抽象構文木(AST)を渡り歩き、ビジター・メソッドの戻り値を使って古いノードを置き換えたり削除したりします。ビジター・メソッドの戻り値が None ならば、ノードはその場から取り去られ、そうでなければ戻り値で置き換えられます。置き換えない場合は戻り値が元のノードそのものであってもかまいません。

それでは例を示しましょう。Name (たとえば foo) を見つけるたび全て data['foo'] に書き換える変換器 (transformer) です:

class RewriteName(NodeTransformer):

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

操作しようとしているノードが子ノードを持つならば、その子ノードの変形も自分で行うか、またはそのノードに対し最初に generic_visit() メソッドを呼び出すか、それを行うのはあなたの責任だということを肝に銘じましょう。

文のコレクションであるようなノード (全ての文のノードが当てはまります) に対して、このビジターは単独のノードではなくノードのリストを返すかもしれません。

NodeTransformer が(たとえば、 lineno のような)位置情報を与えずに(元の木の一部ではなく)新しいノードを導入する場合、 fix_missing_locations() を新しいサブツリーで呼び出して、位置情報を再計算する必要があります。

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

たいてい、変換器の使い方は次のようになります:

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

node 内のツリーのフォーマットされたダンプを返します。主な使い道はデバッグです。 annotate_fields が(デフォルトで)trueの場合、返される文字列はフィールドの名前と値を示します。 annotate_fields がfalseの場合、あいまいさのないフィールド名を省略することにより、結果文字列はよりコンパクトになります。行番号や列オフセットのような属性はデフォルトではダンプされません。これがほ欲しければ、 include_attributes をtrueにセットすることができます。

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.

バージョン 3.9 で変更: 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.

バージョン 3.8 で追加.

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>).

バージョン 3.8 で追加.

コマンドラインからの使用

バージョン 3.9 で追加.

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]

以下のオプションが使用できます:

-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.

参考

外部ドキュメント Green Tree Snakes には Python AST についての詳細が書かれています。

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.