如何獲得模塊中類的定義？

Question

爲什麼在下面的代碼中我無法從模塊collections中獲得Callable的定義？

如何獲取模塊中類的定義？謝謝。

>>> from collections import Callable 
>>> inspect.getsource(Callable) 
Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "/usr/lib/python3.5/inspect.py", line 944, in getsource 
    lines, lnum = getsourcelines(object) 
    File "/usr/lib/python3.5/inspect.py", line 931, in getsourcelines 
    lines, lnum = findsource(object) 
    File "/usr/lib/python3.5/inspect.py", line 788, in findsource 
    raise OSError('could not find class definition') 
OSError: could not find class definition 
>>> inspect.getsourcelines(Callable) 
Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "/usr/lib/python3.5/inspect.py", line 931, in getsourcelines 
    lines, lnum = findsource(object) 
    File "/usr/lib/python3.5/inspect.py", line 788, in findsource 
    raise OSError('could not find class definition') 
OSError: could not find class definition 
>>> inspect.getmodule(Callable) 
<module 'collections.abc' from '/usr/lib/python3.5/collections/abc.py'> 
>>> inspect.getfile(Callable) 
'/usr/lib/python3.5/collections/abc.py' 
>>> inspect.getsourcefile(Callable) 
'/usr/lib/python3.5/collections/abc.py' 

Answer 1

一般來說，這可以通過inspect.getsource輕鬆完成，它可以接受模塊，類，方法，函數，追蹤，框架，或者代碼對象。他們代表的源代碼當然應該用Python編寫，否則會引發錯誤。

在這種特定的情況下，你恰好是不吉利的日子，而Callable是在_collections_abcthe Callable.__module__ name is callections.abc定義：

>>> Callable.__module__ 
'collections.abc' 

這引發getsource了，因爲它不會在_collections_abc看包含Callable的定義但代之以在collections.abc中，其僅導入來自_collections_abc的所有定義：

>>> print(getsource(collections.abc)) 
from _collections_abc import * 
from _collections_abc import __all__ 

通常情況下，getsource沒有問題找到源，例如，在自身：

>>> print(getsource(getsource)) 
def getsource(object): 
    """Return the text of the source code for an object. 

    The argument may be a module, class, method, function, traceback, frame, 
    or code object. The source code is returned as a single string. An 
    OSError is raised if the source code cannot be retrieved.""" 
    lines, lnum = getsourcelines(object) 
    return ''.join(lines) 

在這種特定的情況下，雖然，它（由於Callable.__module__返回collections.abc。）你可以替換__module__與'_collections_abc'一個棘手的方式看到源：

>>> Callable.__module__ = '_collections_abc' 
>>> src = getsource(Callable) 
>>> print(src) 
class Callable(metaclass=ABCMeta): 

    __slots__ =() 

    @abstractmethod 
    def __call__(self, *args, **kwds): 
     return False 

    @classmethod 
    def __subclasshook__(cls, C): 
     if cls is Callable: 
      return _check_methods(C, "__call__") 
     return NotImplemented 

但是這並沒有讓我感到很舒服。

Answer 2

get_source(fullname) 返回指定模塊的源代碼。

所以，你應該返回整個模塊，爲Callable是_collections_abc模塊中定義的，所以你的代碼應該是這樣的：

import _collections_abc 

import inspect 

print(inspect.getsource(_collections_abc)) 

，你可以看到的Callable定義的打印結果。