ast
Délicatement assemblé sur Namek par serge-sans-paille
ast
/me
$ whoami
sguelton
pythran
pour le calcul scientifique en Pythonimport ast
>>> import ast
>>> tree = ast.parse("'galette' + 'saucisse'")
>>> ast.dump(tree)
Module(body=[Expr(value=BinOp(left=Str(s='galette'),
... op=Add(), right=Str(s='saucisse')))])
Module
Expr
BinOp
Str(s='galette')
Add()
Str(s='saucisse')
(python2) >>> import ast
(python2) >>> tree = ast.parse("'print('yaouankiz')")
(python2) >>> ast.dump(tree)
Module(body=[Print(dest=None, values=[Str(s='yaouankiz')], nl=True)])
(python3) >>> import ast
(python3) >>> tree = ast.parse("'print('yaouankiz')")
(python3) >>> ast.dump(tree)
Module(body=[Expr(value=Call(func=Name(id='print', ctx=Load()),
... "args=[Str(s='yaouankiz')], keywords=[], starargs=None, kwargs=None))])
class PP(ast.NodeVisitor):
def __init__(self):
self.depth = 0
def generic_visit(self, node):
print('{}{}'.format(' ' * self.depth, type(node).__name__))
self.depth += 1
super(PP, self).generic_visit(node)
self.depth -= 1
def visit(self, node):
"""Visit a node."""
method = 'visit_' + node.__class__.__name__
visitor = getattr(self, method, self.generic_visit)
return visitor(node)
def generic_visit(self, node):
"""Called if no explicit visitor function exists for a node."""
for field, value in iter_fields(node):
if isinstance(value, list):
for item in value:
if isinstance(item, AST):
self.visit(item)
elif isinstance(value, AST):
self.visit(value)
Comment parcourir indifférement des AST 2 et 3 ?
YieldFrom
ou NameConstant
Print
ou TryFinally
FunctionDef
gagne un champs returns
et ClassDef
gagne un champs keywords
Deux convertisseurs :
ast
(python2) =>
gast
ast
(python3) =>
gast
Q : Pourquoi ne pas convertire le nœud ast.Print
en ast.Call
?
Après tout, c'est pareil !
R : Parce que print = str
et c'est l'enfer
Comment se comporte (en Python 2):
code = '''
from __future__ import print_function
print(1)'''
ast.dump(ast.parse(code))
def _generate_translators(to):
class Translator(ast.NodeTransformer):
'stuff that matters'
# ...
return Translator
AstToGAst = _generate_translators(gast)
GAstToAst = _generate_translators(ast)
def generic_visit(self, node):
cls = type(node).__name__
new_node = getattr(to, cls)() # default constructor
# generate fields recursively
for field in node._fields:
setattr(new_node, field,
self._visit(getattr(node, field)))
# copy any attributes
for attr in getattr(node, '_attributes'):
if hasattr(node, attr):
setattr(new_node, attr,
getattr(node, attr))
# job done!
return new_node
class Ast2ToGAst(AstToGAst):
# stmt
def visit_FunctionDef(self, node):
new_node = gast.FunctionDef(
self._visit(node.name),
self._visit(node.args),
self._visit(node.body),
self._visit(node.decorator_list),
None, # returns
)
ast.copy_location(new_node, node)
return new_node
raise Except, Val, Tbk
raise Except(Val).with_traceback(Tbk)
Ce qui est faux si un zozo surcharge mal (ou dégage) with_traceback
ast
sont dans gast
gast
gast.gast_to_ast
et gast.ast_to_gast
font ce que leur nom les prédispose à fairegast.parse
est équivalent à gast.ast_to_gast(ast.parse(*args))
Vous reprendrez bien un petit peu de grammaire?
module Python
{
mod = Module(stmt* body)
| Interactive(stmt* body)
| Expression(expr body)
-- not really an actual node but useful in Jython's typesystem.
| Suite(stmt* body)
stmt = FunctionDef(identifier name, arguments args,
stmt* body, expr* decorator_list, expr? returns)
| AsyncFunctionDef(identifier name, arguments args,
stmt* body, expr* decorator_list, expr? returns)
| ClassDef(identifier name,
expr* bases,
keyword* keywords,
stmt* body,
expr* decorator_list)
| Return(expr? value)
| Delete(expr* targets)
| Assign(expr* targets, expr value)
| AugAssign(expr target, operator op, expr value)
-- not sure if bool is allowed, can always use int
| Print(expr? dest, expr* values, bool nl)
-- use 'orelse' because else is a keyword in target languages
| For(expr target, expr iter, stmt* body, stmt* orelse)
| AsyncFor(expr target, expr iter, stmt* body, stmt* orelse)
| While(expr test, stmt* body, stmt* orelse)
| If(expr test, stmt* body, stmt* orelse)
| With(withitem* items, stmt* body)
| AsyncWith(withitem* items, stmt* body)
| 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
-- XXX Jython will be different
-- col_offset is the byte offset in the utf8 string the parser uses
attributes (int lineno, int col_offset)
-- BoolOp() can use left & right?
expr = BoolOp(boolop op, expr* values)
| 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)
| Num(object n) -- a number as a PyObject.
| Str(string s) -- need to specify raw, unicode, etc?
| Bytes(bytes s)
| NameConstant(singleton value)
| Ellipsis
-- the following expression can appear in assignment context
| Attribute(expr value, identifier attr, expr_context ctx)
| Subscript(expr value, slice slice, expr_context ctx)
| Starred(expr value, expr_context ctx)
| Name(identifier id, expr_context ctx, expr? annotation)
| List(expr* elts, expr_context ctx)
| Tuple(expr* elts, expr_context ctx)
-- col_offset is the byte offset in the utf8 string the parser uses
attributes (int lineno, int col_offset)
expr_context = Load | Store | Del | AugLoad | AugStore | Param
slice = Slice(expr? lower, expr? upper, expr? step)
| ExtSlice(slice* dims)
| Index(expr value)
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)
excepthandler = ExceptHandler(expr? type, expr? name, stmt* body)
attributes (int lineno, int col_offset)
arguments = (expr* args, expr? vararg, expr* kwonlyargs, expr* kw_defaults,
expr? kwarg, expr* defaults)
-- keyword arguments supplied to call (NULL identifier for **kwargs)
keyword = (identifier? arg, expr value)
-- import name with optional 'as' alias.
alias = (identifier name, identifier? asname)
withitem = (expr context_expr, expr? optional_vars)
}
Permet d'écrire des analysuers de code Python portable :
Et pourquoi pas asteroids
, bandit
, astoptimizer
…
tox
[tox]
envlist = py27,py30,py31,py32,py33,py34,py35
[testenv]
deps=pytest-pep8
commands=py.test --pep8
Petit challenge : compiler une version fonctionnelle de chacun de ses interpreteurs
pip install gast
https://github.com/serge-sans-paille/gast
♥ Logilab ♥ pour avoir soufflé l'idée (ils embauchent)
♥ QuarksLab ♥ pour la liberté (on embauche)
☺ PyConFr ☺ & l'orga pour avoir choisi Roazhon !