问题
What is the proper way to loop over a Python object's methods and call them?
Given the object:
class SomeTest():
def something1(self):
print "something 1"
def something2(self):
print "something 2"
回答1:
You can use the inspect module to get class (or instance) members:
>>> class C(object):
... a = 'blah'
... def b(self):
... pass
...
...
>>> c = C()
>>> inspect.getmembers(c, inspect.ismethod)
[('b', <bound method C.b of <__main__.C object at 0x100498250>>)]
getmembers() returns a list of tuples, where each tuple is (name, member). The second argument to getmembers() is the predicate, which filters the return list (in this case, returning only method objects)
回答2:
Methods vs. functions and other types of callables...
(To address the issue in the comments in Unknown's post.)
First, it should be noted that, in addition to user-defined methods, there are built-in methods, and a built-in method is, as the doc at http://docs.python.org/reference/datamodel.html says, "really a different disguise of a built-in function" (which is a wrapper around a C function.)
As for user-defined methods, as Unknown's cited quote says:
A user-defined method object combines a class, a class instance (or None) and any callable object (normally a user-defined function).
But this does not mean that "anything that defines __call__ and is attached to an object is a method." A method is a callable, but a callable is not necessarily a method. User-defined methods are wrappers around what the quote says.
Hopefully this output (from Python 2.5.2 which I have handy) will show the distinction:
IDLE 1.2.2
>>> class A(object):
x = 7
>>> A # show the class object
<class '__main__.A'>
>>> a = A()
>>> a # show the instance
<__main__.A object at 0x021AFBF0>
>>> def test_func(self):
print self.x
>>> type(test_func) # what type is it?
<type 'function'>
>>> dir(test_func) # what does it have?
['__call__', '__class__', '__delattr__', '__dict__', '__doc__', '__get__',
'__getattribute__', '__hash__', '__init__', '__module__', '__name__',
'__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__',
'__str__', 'func_closure', 'func_code', 'func_defaults', 'func_dict',
'func_doc', 'func_globals', 'func_name']
>>> # But now let's put test_func on the class...
>>> A.test = test_func
>>> type(A.test) # What type does this show?
<type 'instancemethod'>
>>> dir(A.test) # And what does it have?
['__call__', '__class__', '__cmp__', '__delattr__', '__doc__', '__get__',
'__getattribute__', '__hash__', '__init__', '__new__', '__reduce__',
'__reduce_ex__', '__repr__', '__setattr__', '__str__', 'im_class',
'im_func', 'im_self']
>>> # See, we just got a wrapper, and the function is in 'im_func'...
>>> getattr(A.test, 'im_func')
<function test_func at 0x0219F4B0>
>>> # Now to show bound vs. unbound methods...
>>> getattr(a.test, 'im_self') # Accessing it via the instance
<__main__.A object at 0x021AFBF0>
>>> # The instance is itself 'im_self'
>>> a.test()
7
>>> getattr(A.test, 'im_self') # Accessing it via the class returns None...
>>> print getattr(A.test, 'im_self')
None
>>> # It's unbound when accessed that way, so there's no instance in there
>>> # Which is why the following fails...
>>> A.test()
Traceback (most recent call last):
File "<pyshell#25>", line 1, in <module>
A.test()
TypeError: unbound method test_func() must be called with A instance as
first argument (got nothing instead)
>>>
And - editing to add the following additional output, which is also relevant...
>>> class B(object):
pass
>>> b = B()
>>> b.test = test_func # Putting the function on the instance, not class
>>> type(b.test)
<type 'function'>
>>>
I wont add more output, but you could also make a class an attribute of another class or instance, and, even though classes are callable, you would not get a method. Methods are implemented using non-data descriptors, so look up descriptors if you want more info on how they work.
回答3:
This code snippet will call anything it will find in obj and store results in mapping, where key is attribute name — dict((k, v()) for (k, v) in obj.__dict__.iteritems() if k.startswith('something'))
回答4:
Edit
Daniel, you are wrong.
http://docs.python.org/reference/datamodel.html
User-defined methods
A user-defined method object combines a class, a class instance (or None) and any callable object (normally a user-defined function).
Therefore, anything that defines __call__ and is attached to an object is a method.
Answer
The proper way to see what elements an object has is to use the dir() function.
Obviously this example only works for functions that take no arguments.
a=SomeTest()
for varname in dir(a):
var = getattr(a, varname)
if hasattr(var, "__call__"):
var()
来源：https://stackoverflow.com/questions/928990/looping-over-a-python-ironpython-object-methods