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POHow to dynamically create module level functions from methods in a class
 

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  1. POHow to dynamically create module level functions from methods in a class
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    <p>I am trying to dynamically create module level functions from the methods in a class. So for every method in a class, I want to create a function with the same name which creates an instance of the class and then calls the method.</p> <p>The reason I want to do this is so I can take an object-oriented approach to creating Fabric files. Since Fabric will call module level functions but not methods of a class, this is my work-around.</p> <p>I have used the following links to get me started</p> <ul> <li><a href="https://stackoverflow.com/questions/1911281/how-do-you-get-list-of-methods-in-a-python-class">How do I get list of methods in a Python class?</a></li> <li><a href="https://stackoverflow.com/questions/1621350/dynamically-adding-functions-to-a-python-module">dynamically adding functions to a Python module</a></li> <li><a href="https://stackoverflow.com/questions/2933470/how-do-i-call-setattr-on-the-current-module">How do I call setattr() on the current module?</a></li> <li><a href="http://effbot.org/zone/python-getattr.htm" rel="nofollow noreferrer">http://effbot.org/zone/python-getattr.htm</a></li> <li><a href="https://stackoverflow.com/questions/3061/calling-a-function-from-a-string-with-the-functions-name-in-python">Calling a function of a module from a string with the function&#39;s name in Python</a></li> <li><a href="https://stackoverflow.com/questions/1142068/how-to-modify-the-local-namespace-in-python">How to modify the local namespace in python</a></li> </ul> <p>And I have come up with the following code</p> <pre><code>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() </code></pre> <p>And I get the following error</p> <pre><code>['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__', &lt;unbound method TestClass.__init__&gt;) code: &lt;code object newfunc_template at 0x7f8800a28d50, file "test.py", line 85&gt; method_name: __init__ ('method1', &lt;unbound method TestClass.method1&gt;) code: &lt;code object newfunc_template at 0x7f8800a28d50, file "test.py", line 85&gt; method_name: method1 ('method2', &lt;unbound method TestClass.method2&gt;) code: &lt;code object newfunc_template at 0x7f8800a28d50, file "test.py", line 85&gt; 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 &lt;module&gt; method1('arg1') File "test.py", line 88, in newfunc_template return func(*args, **kwargs) TypeError: method2() takes exactly 1 argument (2 given) </code></pre> <p>It seems to be reusing the reference to the function? Any ideas?</p> <p>UPDATE: Here is the working code with Ned Batchelder's fix</p> <pre><code>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) </code></pre> <p>UPDATE 2: Here is my blog post on the subject: <a href="http://www.saltycrane.com/blog/2010/09/class-based-fabric-scripts-metaprogramming-hack/" rel="nofollow noreferrer">http://www.saltycrane.com/blog/2010/09/class-based-fabric-scripts-metaprogramming-hack/</a></p>
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