如何从类中的方法动态创建模块级函数

Question

我正在尝试从类中的方法动态创建模块级函数。所以对于一个类中的每个方法，我想创建一个同名的函数，它创建一个类的实例，然后调用该方法。

我想这样做的原因是我可以采用面向对象的方法来创建 Fabric 文件。由于 Fabric 将调用模块级函数而不是类的方法，这是我的解决方法。

我使用以下链接让我开始使用

• How do I get list of methods in a Python class?
• dynamically adding functions to a Python module
• How do I call setattr() on the current module?
• http://effbot.org/zone/python-getattr.htm
• Calling a function of a module from a string with the function's name in Python
• How to modify the local namespace in python

我想出了以下代码

import inspect
import sys
import types

class TestClass(object):
    def __init__(self):
        pass

    def method1(self, arg1):
        print 'method 1 %s' % arg1

    def method2(self):
        print 'method 2'

def fabric_class_to_function_magic(module_name):
    # get the module as an object
    print module_name
    module_obj = sys.modules[module_name]
    print dir(module_obj)

    # Iterate over the methods of the class and dynamically create a function
    # for each method that calls the method and add it to the current module
    for method in inspect.getmembers(TestClass, predicate=inspect.ismethod):
        print
        print method
        method_name, method_obj = method

        # create a new template function which calls the method
        def newfunc_template(*args, **kwargs):
            tc = TestClass()
            func = getattr(tc, method_name)
            return func(*args, **kwargs)

        # create the actual function
        print 'code: ', newfunc_template.func_code
        print 'method_name: ', method_name
        newfunc = types.FunctionType(newfunc_template.func_code,
                                     {'TestClass': TestClass,
                                      'getattr': getattr,
                                      'method_name': method_name,
                                      },
                                     name=method_name,
                                     argdefs=newfunc_template.func_defaults,
                                     closure=newfunc_template.func_closure,
                                     )

        # add the new function to the current module
        setattr(module_obj, method_name, newfunc)

# test the dynamically created module level function
thismodule = sys.modules[__name__]
print dir(thismodule)
fabric_class_to_function_magic(__name__)
print dir(thismodule)
method1('arg1')
method2()

我收到以下错误

['TestClass', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'fabric_class_to_function_magic', 'inspect', 'sys', 'thismodule', 'types']
__main__
['TestClass', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'fabric_class_to_function_magic', 'inspect', 'sys', 'thismodule', 'types']

('__init__', <unbound method TestClass.__init__>)
code:  <code object newfunc_template at 0x7f8800a28d50, file "test.py", line 85>
method_name:  __init__

('method1', <unbound method TestClass.method1>)
code:  <code object newfunc_template at 0x7f8800a28d50, file "test.py", line 85>
method_name:  method1

('method2', <unbound method TestClass.method2>)
code:  <code object newfunc_template at 0x7f8800a28d50, file "test.py", line 85>
method_name:  method2
['TestClass', '__builtins__', '__doc__', '__file__', '__init__', '__name__', '__package__', 'fabric_class_to_function_magic', 'inspect', 'method1', 'method2', 'sys', 'thismodule', 'types']
Traceback (most recent call last):
  File "test.py", line 111, in <module>
    method1('arg1')
  File "test.py", line 88, in newfunc_template
    return func(*args, **kwargs)
TypeError: method2() takes exactly 1 argument (2 given)

似乎是在重用对函数的引用？有什么想法吗？

更新：这是 Ned Batchelder 修复的工作代码

def fabric_class_to_function_magic(module_name):
    # get the module as an object
    module_obj = sys.modules[module_name]

    # Iterate over the methods of the class and dynamically create a function
    # for each method that calls the method and add it to the current module
    for method in inspect.getmembers(TestClass, predicate=inspect.ismethod):
        method_name, method_obj = method

        # get the bound method
        tc = TestClass()
        func = getattr(tc, method_name)

        # add the function to the current module
        setattr(module_obj, method_name, func)

更新 2：这是我关于该主题的博文：http://www.saltycrane.com/blog/2010/09/class-based-fabric-scripts-metaprogramming-hack/

Answer 1

您对解决方案的思考过度。把fabric_class_to_function_magic的结尾改成这样：

    tc = TestClass()
    func = getattr(tc, method_name)

    # add the new function to the current module
    setattr(module_obj, method_name, func)

而且效果很好。无需创建新的函数对象，getattr 已经在对象上返回了一个。 getattr 返回的绑定方法是一个可调用的东西。只需将其分配给您的模块属性，就可以了。

Answer 2

其实你的代码是对的，但是当 return func(*args, **kwargs) 执行时，args 会传递空元组，如 () 并且你的 method2 中没有参数，所以它会引发这样的异常，

解决您的问题的快速方法是，例如

class TestClass(object):
    def __init__(self):
        pass

    def method1(self, arg1):
        print 'method 1 %s' % arg1

    def method2(self, *args, **kw):
        print 'method 2'