Combining @staticmethod with other decorators is broken

Consider

def debug(fun):
    print(fun)
    return fun

class A(object):
    @staticmethod
    @debug
    def foo(self):
        return self

In Python, this correctly prints <function foo at 0x7f4d305df410>. In Cython, this wrongly prints <staticmethod object at 0x7f4d30e5e718>.

When doing the same with a Cython cdef class, the decorators are somehow applied twice: the output becomes

<staticmethod object at 0x7f4d30e5eb40>
<staticmethod object at 0x7f4d305e52f0>

Migrated from http://trac.cython.org/ticket/880

[linuxhenhao]

For peoplo who facing the same issue here, I got a method to work around this problem. convert a

class A:
    @staticmethod
    @decorator
    def test():
          pass

to

class A:
    def test():
          pass
    test = staticmethod(decorator(test))

A simple implementation of this kind of conversion using ast and astunparse is:

import ast, astunparse


class RewriteFuncdef(ast.NodeTransformer):
    def visit_ClassDef(self, node):
        for index, sub_node in enumerate(node.body):
            if not isinstance(sub_node, ast.FunctionDef):
                continue
                
            decorators = sub_node.decorator_list
            if self.need_rewrite(decorators):
                new_funcdef, assign = self.convert_func_def(sub_node)
                node.body.pop(index)
                node.body.insert(index ,assign)
                node.body.insert(index, new_funcdef)
        return node
                
    def need_rewrite(self, decorators) -> bool:
        for decorator in decorators:
            if isinstance(decorator, ast.Name) and decorator.id == "staticmethod":
                return True
        return False
    
    def convert_func_def(self, func_def):
        new_funcd = ast.FunctionDef(name=func_def.name, body=func_def.body, args=func_def.args, returns=func_def.returns, decorator_list=[])
        decorators = func_def.decorator_list
        a_name = ast.Name(id=func_def.name)
        a_value = self.gen_assign_value(a_name, decorators)
        assign = ast.Assign(targets=[a_name], value=a_value)
        return new_funcd, assign
    
    def gen_assign_value(self, func_name, decorators):
        args = [func_name]
        for decorator in reversed(decorators):
            args = [ast.Call(func=decorator, args=args, keywords=[])]
        return args[0]

module = ast.parse(open("static.py").read())
transformer = RewriteFuncdef()
transformer.visit(module)
generated_content = astunparse.unparse(module)

with open("new_file.py", "w") as f:
      f.write(generated_content)

Hope this can help somebody.

[da-woods]

FWIW there is a PR that should fix this issue https://github.com/cython/cython/pull/3966 - testing that PR and letting me know whether it works or not for your would be useful. We don’t really need more comments saying “I hope this is fixed soon” though.