Getting module path string from a class instance

Tue Nov 13 03:49:42 EST 2012

On 2012年11月13日 07:54:32 +0000, Some Developer wrote:
> On 13/11/2012 07:19, Steven D'Aprano wrote:
>> On 2012年11月13日 06:38:31 +0000, Some Developer wrote:
>>>>> I'm trying to find a way to get a string of the module path of a
>>> class.
>>>>>> So for instance say I have class Foo and it is in a module called
>>> my.module. I want to be able to get a string that is equal to this:
>>> "my.module.Foo". I'm aware of the __repr__ method but it does not do
>>> what I want it to do in this case.
>>>>>> Can anyone offer any advice at all?
>> py> from multiprocessing.pool import Pool py> repr(Pool)
>> "<class 'multiprocessing.pool.Pool'>"
>>>> Seems pretty close to what you ask for. You can either pull that string
>> apart:
>>>> py> s = repr(Pool)
>> py> start = s.find("'")
>> py> end = s.rfind("'")
>> py> s[start+1:end]
>> 'multiprocessing.pool.Pool'
>>>> or you can construct it yourself:
>>>> py> Pool.__module__ + '.' + Pool.__name__ 'multiprocessing.pool.Pool'
>>>>> Yeah I considered doing it this way but was wary of that method because
> of possible changes to the implementation of the __repr__ method in the
> upstream code. If the Django developers don't consider the __repr__
> method a public API then it could change in the future breaking my code.

I didn't call SomeClass.__repr__. That is an implementation detail of 
SomeClass, and could change.
I called repr(SomeClass), which calls the *metaclass* __repr__. That is 
less likely to change, although not impossible.
If you're worried, just use the second way:
SomeClass.__module__ + '.' + SomeClass.__name__

> Of course this might not happen but I was hoping that there was a more 
> generic way of doing it that did not rely on a certain implementation 
> being in existence.

SomeClass.__name__ is the official way to get the name of a class; 
SomeClass.__module__ is the official way to get the name of the module or 
package it comes from.
-- 
Steven