Hướng dẫn dùng ast python python
Source code: Lib/ast.py Show The An abstract syntax tree can be generated by passing Abstract Grammar¶The abstract grammar is currently defined as follows: -- 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) | Match(expr subject, match_case* cases) | 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) attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset) withitem = (expr context_expr, expr? optional_vars) match_case = (pattern pattern, expr? guard, stmt* body) pattern = MatchValue(expr value) | MatchSingleton(constant value) | MatchSequence(pattern* patterns) | MatchMapping(expr* keys, pattern* patterns, identifier? rest) | MatchClass(expr cls, pattern* patterns, identifier* kwd_attrs, pattern* kwd_patterns) | MatchStar(identifier? name) -- The optional "rest" MatchMapping parameter handles capturing extra mapping keys | MatchAs(pattern? pattern, identifier? name) | MatchOr(pattern* patterns) attributes (int lineno, int col_offset, int end_lineno, int end_col_offset) type_ignore = TypeIgnore(int lineno, string tag) } Node classes¶classast. AST ¶This is the base of all AST node classes. The actual node classes are derived from the There is one class defined for each left-hand side symbol in the abstract grammar (for example, _fields ¶Each concrete class has an attribute Each instance of a concrete class has one attribute for each child node, of the type as defined in the grammar. For example,
If these attributes are marked as optional in the grammar (using a question mark), the value might be lineno ¶ col_offset ¶
end_lineno ¶ end_col_offset ¶Instances of 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 The constructor of a class
For example, to create and populate an 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 or the more compact node = ast.UnaryOp(ast.USub(), ast.Constant(5, lineno=0, col_offset=0), lineno=0, col_offset=0) Changed in version 3.8: Class Changed in version 3.9: Simple indices are represented by their value, extended slices are represented as tuples. Deprecated since version 3.8: Old classes Deprecated since version 3.9: Old classes Note The descriptions of the specific node classes displayed here were initially adapted from the fantastic Green Tree Snakes project and all its contributors. Literals¶classast. Constant (value)¶A constant value. The >>> 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
ast. JoinedStr (values)¶An f-string, comprising a series of >>> 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. >>> 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. >>> 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. When doing dictionary unpacking using dictionary literals the expression to be expanded goes in the >>> 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¶classast. Name (id, ctx)¶
A variable name. 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 >>> print(ast.dump(ast.parse('a, *b = it'), indent=4)) Module( body=[ Assign( targets=[ Tuple( elts=[ Name(id='a', ctx=Store()), Starred( value=Name(id='b', ctx=Store()), ctx=Store())], ctx=Store())], value=Name(id='it', ctx=Load()))], type_ignores=[]) Expressions¶classast. 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. >>> 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. ast. UAdd ¶ class ast. USub ¶ class
ast. Not ¶ class ast. Invert ¶Unary operator tokens. >>> 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). >>> 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. classast. BoolOp (op, values)¶A boolean
operation, ‘or’ or ‘and’. This doesn’t include >>> 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. classast. Compare (left, ops, comparators)¶A comparison of two or more values. >>> 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. classast. Call (func, args, keywords, starargs, kwargs)¶A function call.
When creating a >>> 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. ast. IfExp (test, body, orelse)¶An
expression such as >>> 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. >>> 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)¶
>>> 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¶classast. Subscript (value, slice, ctx)¶A subscript, such as >>> 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 >>> 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¶classast. 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.
>>> 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
>>> 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¶classast. Assign (targets, value, type_comment)¶An assignment. Multiple nodes in
>>> 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. >>> 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 The >>> 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 >>> 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. >>> 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 >>> 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 >>> 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¶classast. Import (names)¶An import statement. >>> 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 >>> 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. >>> 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¶Note Optional clauses such as ast. If (test, body,
orelse)¶An
>>> 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
>>> 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 >> 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 >>> 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)¶
>>> 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 >>> 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
ast. withitem (context_expr, optional_vars)¶A single context manager in a >>> 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=[]) Pattern matching¶classast. Match (subject, cases)¶
A ast. match_case (pattern, guard,
body)¶A single case pattern in a The
>>> print(ast.dump(ast.parse(""" ... match x: ... case [x] if x>0: ... ... ... case tuple(): ... ... ... """), indent=4)) Module( body=[ Match( subject=Name(id='x', ctx=Load()), cases=[ match_case( pattern=MatchSequence( patterns=[ MatchAs(name='x')]), guard=Compare( left=Name(id='x', ctx=Load()), ops=[ Gt()], comparators=[ Constant(value=0)]), body=[ Expr( value=Constant(value=Ellipsis))]), match_case( pattern=MatchClass( cls=Name(id='tuple', ctx=Load()), patterns=[], kwd_attrs=[], kwd_patterns=[]), body=[ Expr( value=Constant(value=Ellipsis))])])], type_ignores=[])class ast. MatchValue (value)¶A match literal or value pattern that compares by equality. >>> print(ast.dump(ast.parse(""" ... match x: ... case "Relevant": ... ... ... """), indent=4)) Module( body=[ Match( subject=Name(id='x', ctx=Load()), cases=[ match_case( pattern=MatchValue( value=Constant(value='Relevant')), body=[ Expr( value=Constant(value=Ellipsis))])])], type_ignores=[])class ast. MatchSingleton (value)¶A match literal pattern that compares by identity. >>> print(ast.dump(ast.parse(""" ... match x: ... case None: ... ... ... """), indent=4)) Module( body=[ Match( subject=Name(id='x', ctx=Load()), cases=[ match_case( pattern=MatchSingleton(value=None), body=[ Expr( value=Constant(value=Ellipsis))])])], type_ignores=[])class ast. MatchSequence (patterns)¶A match sequence pattern. >>> print(ast.dump(ast.parse(""" ... match x: ... case [1, 2]: ... ... ... """), indent=4)) Module( body=[ Match( subject=Name(id='x', ctx=Load()), cases=[ match_case( pattern=MatchSequence( patterns=[ MatchValue( value=Constant(value=1)), MatchValue( value=Constant(value=2))]), body=[ Expr( value=Constant(value=Ellipsis))])])], type_ignores=[])class ast. MatchStar (name)¶Matches the rest of the sequence in a variable length match sequence pattern. If >>> print(ast.dump(ast.parse(""" ... match x: ... case [1, 2, *rest]: ... ... ... case [*_]: ... ... ... """), indent=4)) Module( body=[ Match( subject=Name(id='x', ctx=Load()), 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))])])], type_ignores=[])class ast. MatchMapping (keys, patterns, rest)¶A match mapping pattern. 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 >>> print(ast.dump(ast.parse(""" ... match x: ... case {1: _, 2: _}: ... ... ... case {**rest}: ... ... ... """), indent=4)) Module( body=[ Match( subject=Name(id='x', ctx=Load()), 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(keys=[], patterns=[], rest='rest'), body=[ Expr( value=Constant(value=Ellipsis))])])], type_ignores=[])class ast. MatchClass (cls, patterns, kwd_attrs, kwd_patterns)¶A match 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', ctx=Load()), cases=[ match_case( pattern=MatchClass( cls=Name(id='Point2D', ctx=Load()), patterns=[ MatchValue( value=Constant(value=0)), MatchValue( value=Constant(value=0))], kwd_attrs=[], kwd_patterns=[]), body=[ Expr( value=Constant(value=Ellipsis))]), match_case( pattern=MatchClass( cls=Name(id='Point3D', ctx=Load()), patterns=[], 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))])])], type_ignores=[])class ast. MatchAs (pattern,
name)¶A match “as-pattern”, capture pattern or wildcard pattern. The >>> print(ast.dump(ast.parse(""" ... match x: ... case [x] as y: ... ... ... case _: ... ... ... """), indent=4)) Module( body=[ Match( subject=Name(id='x', ctx=Load()), 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))])])], type_ignores=[])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 >>> print(ast.dump(ast.parse(""" ... match x: ... case [x] | (y): ... ... ... """), indent=4)) Module( body=[ Match( subject=Name(id='x', ctx=Load()), cases=[ match_case( pattern=MatchOr( patterns=[ MatchSequence( patterns=[ MatchAs(name='x')]), MatchAs(name='y')]), body=[ Expr( value=Constant(value=Ellipsis))])])], type_ignores=[]) Function and class definitions¶classast. FunctionDef (name, args, body, decorator_list, returns, type_comment)¶A function definition.
ast. Lambda (args, body)¶
>>> 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.
ast. arg (arg, annotation, type_comment)¶A single argument in a list.
>>> 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 >>> 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 >>> 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)¶
>>> 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.
>>> 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¶classast. AsyncFunctionDef (name, args,
body, decorator_list, returns, type_comment)¶An ast. Await (value)¶An >>> 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)¶
Note When a string is parsed by ast Helpers¶Apart
from the node classes, the ast. parse (source, filename='Parse the source into an AST node. Equivalent to If In addition, if Also, setting If source contains a null character (’0’), Warning Note that successfully parsing source code into an AST object doesn’t guarantee that the source code provided is valid Python code that can be executed as the compilation step can raise further
In particular,
Warning It is possible to crash the Python interpreter with a sufficiently large/complex string due to stack depth limitations in Python’s AST compiler. Changed in version 3.8: Added ast. unparse (ast_obj)¶Unparse
an Warning The produced code string will not necessarily be
equal to the original code that generated the Warning Trying to unparse a highly complex expression would result with New in version 3.9. ast. literal_eval (node_or_string)¶Safely evaluate an expression node or a string containing a Python literal or container display. The string or node provided may only consist of the following Python literal structures: strings, bytes, numbers, tuples, lists, dicts,
sets, booleans, This can be used for safely evaluating strings containing Python values from untrusted sources without the need to parse the values oneself. It is not capable of evaluating arbitrarily complex expressions, for example involving operators or indexing. Changed in version 3.2: Now allows bytes and set literals. Changed in version 3.9: Now supports creating empty sets with Changed in version 3.10: For string inputs, leading spaces and tabs are now stripped. ast. get_docstring (node, clean=True)¶Return the docstring of the given node (which must be a
ast. get_source_segment (source, node, *, padded=False)¶
Get source code segment of the source that generated node. If some location information ( If padded is New in version 3.8. ast. fix_missing_locations (node)¶When you compile a node tree with 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 ( ast. iter_fields (node)¶Yield a tuple of ast. iter_child_nodes (node)¶Yield all direct child nodes of node, that is, all fields that are nodes and all items of fields that are lists of nodes. ast. walk (node)¶Recursively yield all descendant nodes in the tree starting at node (including node itself), in no specified order. This is useful if you only want to modify nodes in place and don’t care about the context. classast. NodeVisitor ¶A node visitor base class that walks the abstract syntax tree and calls a visitor function for every node found. This function may return a value which is forwarded by the This class is meant to be subclassed, with the subclass adding visitor methods. visit (node)¶Visit a node. The default implementation calls the method called generic_visit (node)¶This visitor calls
Note that child nodes of nodes that have a custom visitor method won’t be visited unless the visitor calls Don’t use the
Deprecated since version 3.8: Methods ast. NodeTransformer ¶A The Here is an example transformer that rewrites all occurrences of name lookups ( class RewriteName(NodeTransformer): def visit_Name(self, node): return Subscript( value=Name(id='data', ctx=Load()), slice=Constant(value=node.id), ctx=node.ctx ) Keep in mind that if the node you’re operating on has child nodes you must either transform the child nodes yourself or call the For nodes that were part of a collection of statements (that applies to all statement nodes), the visitor may also return a list of nodes rather than just a single node. If
tree = ast.parse('foo', mode='eval') new_tree = fix_missing_locations(RewriteName().visit(tree)) Usually you use the transformer like this: node = YourTransformer().visit(node) ast. dump (node, annotate_fields=True, include_attributes=False, *,
indent=None)¶Return a formatted dump of the tree in node. This is mainly useful for debugging purposes. If annotate_fields is true (by default), the returned string will show the names and the values for fields. If annotate_fields is false, the result string will be more compact by omitting unambiguous field names. Attributes such as line numbers and column offsets are not dumped by default. If this is wanted, include_attributes can be set to true. 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 Changed in version 3.9: Added the indent option. Compiler Flags¶The following flags may be passed to
ast. PyCF_ALLOW_TOP_LEVEL_AWAIT ¶Enables support for top-level New in version 3.8. ast. PyCF_ONLY_AST ¶Generates and returns an abstract syntax tree instead of returning a compiled code object. Enables support for PEP 484 and
PEP 526 style type comments ( New in version 3.8. Command-Line Usage¶New in version 3.9. The
python -m ast [-m The following options are accepted: -h
, --help ¶Show the help message and exit. -m ¶ --mode ¶Specify what kind of code must be compiled, like the mode argument in Don’t parse type comments. -a
, --include-attributes ¶Include attributes such as line numbers and column offsets. -i ¶ --indent ¶Indentation of nodes in AST (number of spaces). If See also Green Tree Snakes, an external documentation resource, has good details on working with Python ASTs. 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. |