如何在Python中檢查對象所具有的方法？

Question

例如，一個列表。

l1 = [1,5,7] 如何檢查它的方法？

（l1.append，例如）

或字符串... string.lower（

Answer 1

您可以使用dir得到一個列表中的任何對象的方法。這是非常有用的交互式提示：

>>> dir(l1) 
['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__delslice__', '__doc__', '__eq__', 
'__ge__', '__getattribute__', '__getitem__', '__getslice__', '__gt__', '__hash__', '__iadd__', '__imul__', 
'__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', 
'__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__setslice__', 
'__str__', 'append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort'] 

有趣的方法通常是那些沒有開始用下劃線您可以編寫自己的目錄版本，如果你想忽略開始用下劃線名稱：

>>> mydir = lambda a:[x for x in dir(a) if not x.startswith('_')] 
>>> mydir([]) 
['append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort'] 

Answer 2

如果安裝IPython，那麼你可以這樣做：

% ipython 
Python 2.6.4 (r264:75706, Nov 2 2009, 14:38:03) 
Type "copyright", "credits" or "license" for more information. 

IPython 0.10 -- An enhanced Interactive Python. 
?   -> Introduction and overview of IPython's features. 
%quickref -> Quick reference. 
help  -> Python's own help system. 
object? -> Details about 'object'. ?object also works, ?? prints more. 

In [1]: l1=[1,5,7] 

In [2]: l1. 
l1.__add__   l1.__getslice__  l1.__new__   l1.append 
l1.__class__   l1.__gt__   l1.__reduce__  l1.count 
l1.__contains__  l1.__hash__   l1.__reduce_ex__  l1.extend 
l1.__delattr__  l1.__iadd__   l1.__repr__   l1.index 
l1.__delitem__  l1.__imul__   l1.__reversed__  l1.insert 
l1.__delslice__  l1.__init__   l1.__rmul__   l1.pop 
l1.__doc__   l1.__iter__   l1.__setattr__  l1.remove 
l1.__eq__   l1.__le__   l1.__setitem__  l1.reverse 
l1.__format__  l1.__len__   l1.__setslice__  l1.sort 
l1.__ge__   l1.__lt__   l1.__sizeof__   
l1.__getattribute__ l1.__mul__   l1.__str__   
l1.__getitem__  l1.__ne__   l1.__subclasshook__ 

In [2]: l1. 

就上線，你鍵入對象名稱，一段時間，然後按TAB。 IPython然後列出對象的所有屬性。

我發現IPython是探索對象屬性的寶貴工具。它比標準的Python交互式提示使用起來要方便得多。在其他時髦的東西，把問號的對象後，給你的文檔字符串：

In [6]: d.update? 
Type:  builtin_function_or_method 
Base Class: <type 'builtin_function_or_method'> 
String Form: <built-in method update of dict object at 0xa3c024c> 
Namespace: Interactive 
Docstring: 
    D.update(E, **F) -> None. Update D from dict/iterable E and F. 
    If E has a .keys() method, does:  for k in E: D[k] = E[k] 
    If E lacks .keys() method, does:  for (k, v) in E: D[k] = v 
    In either case, this is followed by: for k in F: D[k] = F[k] 

而且，如果可用，兩個問號給你它的源代碼：

In [18]: np.sum?? 
Type:  function 
Base Class: <type 'function'> 
String Form: <function sum at 0x9c501ec> 
Namespace: Interactive 
File:  /usr/lib/python2.6/dist-packages/numpy/core/fromnumeric.py 
Definition: np.sum(a, axis=None, dtype=None, out=None) 
Source: 
def sum(a, axis=None, dtype=None, out=None): 
... 
    if isinstance(a, _gentype): 
     res = _sum_(a) 
     if out is not None: 
      out[...] = res 
      return out 
     return res 
    try: 
     sum = a.sum 
    except AttributeError: 
     return _wrapit(a, 'sum', axis, dtype, out) 
    return sum(axis, dtype, out) 

Answer 3

碰巧，列表實例的所有成員都是方法。如果不是這樣的話，你可以這樣做：

l1 = [1, 5 , 7] 
print [name for name in dir(l1) if type(getattr(l1, name) == type(l1.append))] 

這將排除成員是不是方法。

Answer 4

你可能想看看getmembers功能inspect模塊

In [1]: import inspect 

In [2]: inspect? 
Type:  module 
Base Class: <type 'module'> 
String Form: <module 'inspect' from '/usr/lib/python2.6/inspect.pyc'> 
Namespace: Interactive 
File:  /usr/lib/python2.6/inspect.py 
Docstring: 
    Get useful information from live Python objects. 

    This module encapsulates the interface provided by the internal special 
    attributes (func_*, co_*, im_*, tb_*, etc.) in a friendlier fashion. 
    It also provides some help for examining source code and class layout. 

    Here are some of the useful functions provided by this module: 

     ismodule(), isclass(), ismethod(), isfunction(), isgeneratorfunction(), 
      isgenerator(), istraceback(), isframe(), iscode(), isbuiltin(), 
      isroutine() - check object types 
     getmembers() - get members of an object that satisfy a given condition 

     getfile(), getsourcefile(), getsource() - find an object's source code 
     getdoc(), getcomments() - get documentation on an object 
     getmodule() - determine the module that an object came from 
     getclasstree() - arrange classes so as to represent their hierarchy 

     getargspec(), getargvalues() - get info about function arguments 
     formatargspec(), formatargvalues() - format an argument spec 
     getouterframes(), getinnerframes() - get info about frames 
     currentframe() - get the current stack frame 
     stack(), trace() - get info about frames on the stack or in a traceback 

In [3]: l1=[1,5,7] 

In [4]: inspect.getmembers(l1) 
Out[4]: 
[('__add__', <method-wrapper '__add__' of list object at 0xa38716c>), 
('__class__', <type 'list'>), 
('__contains__', <method-wrapper '__contains__' of list object at 0xa38716c>), 
('__delattr__', <method-wrapper '__delattr__' of list object at 0xa38716c>), 
('__delitem__', <method-wrapper '__delitem__' of list object at 0xa38716c>), 
('__delslice__', <method-wrapper '__delslice__' of list object at 0xa38716c>), 
('__doc__', 
    "list() -> new list\nlist(sequence) -> new list initialized from sequence's items"), 
('__eq__', <method-wrapper '__eq__' of list object at 0xa38716c>), 
('__format__', <built-in method __format__ of list object at 0xa38716c>), 
('__ge__', <method-wrapper '__ge__' of list object at 0xa38716c>), 
('__getattribute__', 
    <method-wrapper '__getattribute__' of list object at 0xa38716c>), 
('__getitem__', <built-in method __getitem__ of list object at 0xa38716c>), 
('__getslice__', <method-wrapper '__getslice__' of list object at 0xa38716c>), 
('__gt__', <method-wrapper '__gt__' of list object at 0xa38716c>), 
('__hash__', None), 
('__iadd__', <method-wrapper '__iadd__' of list object at 0xa38716c>), 
('__imul__', <method-wrapper '__imul__' of list object at 0xa38716c>), 
('__init__', <method-wrapper '__init__' of list object at 0xa38716c>), 
('__iter__', <method-wrapper '__iter__' of list object at 0xa38716c>), 
('__le__', <method-wrapper '__le__' of list object at 0xa38716c>), 
('__len__', <method-wrapper '__len__' of list object at 0xa38716c>), 
('__lt__', <method-wrapper '__lt__' of list object at 0xa38716c>), 
('__mul__', <method-wrapper '__mul__' of list object at 0xa38716c>), 
('__ne__', <method-wrapper '__ne__' of list object at 0xa38716c>), 
('__new__', <built-in method __new__ of type object at 0x822be40>), 
('__reduce__', <built-in method __reduce__ of list object at 0xa38716c>), 
('__reduce_ex__', 
    <built-in method __reduce_ex__ of list object at 0xa38716c>), 
('__repr__', <method-wrapper '__repr__' of list object at 0xa38716c>), 
('__reversed__', <built-in method __reversed__ of list object at 0xa38716c>), 
('__rmul__', <method-wrapper '__rmul__' of list object at 0xa38716c>), 
('__setattr__', <method-wrapper '__setattr__' of list object at 0xa38716c>), 
('__setitem__', <method-wrapper '__setitem__' of list object at 0xa38716c>), 
('__setslice__', <method-wrapper '__setslice__' of list object at 0xa38716c>), 
('__sizeof__', <built-in method __sizeof__ of list object at 0xa38716c>), 
('__str__', <method-wrapper '__str__' of list object at 0xa38716c>), 
('__subclasshook__', 
    <built-in method __subclasshook__ of type object at 0x822be40>), 
('append', <built-in method append of list object at 0xa38716c>), 
('count', <built-in method count of list object at 0xa38716c>), 
('extend', <built-in method extend of list object at 0xa38716c>), 
('index', <built-in method index of list object at 0xa38716c>), 
('insert', <built-in method insert of list object at 0xa38716c>), 
('pop', <built-in method pop of list object at 0xa38716c>), 
('remove', <built-in method remove of list object at 0xa38716c>), 
('reverse', <built-in method reverse of list object at 0xa38716c>), 
('sort', <built-in method sort of list object at 0xa38716c>)] 

Answer 5

互動Python有一個help功能，您可以與任何使用：

>>> help(list) 
Help on class list in module __builtin__: 

class list(object) 
| list() -> new list 
| list(sequence) -> new list initialized from sequence´s items 
| 
| Methods defined here: 
| 
| __add__(...) 
|  x.__add__(y) <==> x+y 
| 
| __contains__(...) 
|  x.__contains__(y) <==> y in x 
| 
| __delitem__(...) 
|  x.__delitem__(y) <==> del x[y] 
| 
| __delslice__(...) 
|  x.__delslice__(i, j) <==> del x[i:j] 
| 
|  Use of negative indices is not supported. 
| 
| __eq__(...) 
|  x.__eq__(y) <==> x==y 
| 
| __ge__(...) 
|  x.__ge__(y) <==> x>=y 
| 
| __getattribute__(...) 
|  x.__getattribute__('name') <==> x.name 
| 
| __getitem__(...) 
|  x.__getitem__(y) <==> x[y] 
| 
| __getslice__(...) 
|  x.__getslice__(i, j) <==> x[i:j] 
| 
|  Use of negative indices is not supported. 
| 
| __gt__(...) 
|  x.__gt__(y) <==> x>y 
| 
| __iadd__(...) 
|  x.__iadd__(y) <==> x+=y 
| 
| __imul__(...) 
|  x.__imul__(y) <==> x*=y 
| 
| __init__(...) 
|  x.__init__(...) initializes x; see x.__class__.__doc__ for signature 
| 
| __iter__(...) 
|  x.__iter__() <==> iter(x) 
| 
| __le__(...) 
|  x.__le__(y) <==> x<=y 
| 
| __len__(...) 
|  x.__len__() <==> len(x) 
| 
| __lt__(...) 
|  x.__lt__(y) <==> x<y 
| 
| __mul__(...) 
|  x.__mul__(n) <==> x*n 
| 
| __ne__(...) 
|  x.__ne__(y) <==> x!=y 
| 
| __repr__(...) 
|  x.__repr__() <==> repr(x) 
| 
| __reversed__(...) 
|  L.__reversed__() -- return a reverse iterator over the list 
| 
| __rmul__(...) 
|  x.__rmul__(n) <==> n*x 
| 
| __setitem__(...) 
|  x.__setitem__(i, y) <==> x[i]=y 
| 
| __setslice__(...) 
|  x.__setslice__(i, j, y) <==> x[i:j]=y 
| 
|  Use of negative indices is not supported. 
| 
| __sizeof__(...) 
|  L.__sizeof__() -- size of L in memory, in bytes 
| 
| append(...) 
|  L.append(object) -- append object to end 
| 
| count(...) 
|  L.count(value) -> integer -- return number of occurrences of value 
| 
| extend(...) 
|  L.extend(iterable) -- extend list by appending elements from the iterable 
| 
| index(...) 
|  L.index(value, [start, [stop]]) -> integer -- return first index of value. 
|  Raises ValueError if the value is not present. 
| 
| insert(...) 
|  L.insert(index, object) -- insert object before index 
| 
| pop(...) 
|  L.pop([index]) -> item -- remove and return item at index (default last). 
|  Raises IndexError if list is empty or index is out of range. 
| 
| remove(...) 
|  L.remove(value) -- remove first occurrence of value. 
|  Raises ValueError if the value is not present. 
| 
| reverse(...) 
|  L.reverse() -- reverse *IN PLACE* 
| 
| sort(...) 
|  L.sort(cmp=None, key=None, reverse=False) -- stable sort *IN PLACE*; 
|  cmp(x, y) -> -1, 0, 1 
| 
| ---------------------------------------------------------------------- 
| Data and other attributes defined here: 
| 
| __hash__ = None 
| 
| __new__ = <built-in method __new__ of type object at 0x1E1CF100> 
|  T.__new__(S, ...) -> a new object with type S, a subtype of T 

Answer 6

如果對象（通常可能成爲一個模塊）有很多使用dir的方法或屬性，或者ipython的TAB完成可以得到複雜的跟蹤。

在這種情況下，我在下面的例子中使用的過濾器，如：

filter(lambda s: 'sin' in s.lower(), dir(numpy)) 

導致

['arcsin', 
'arcsinh', 
'csingle', 
'isinf', 
'isposinf', 
'sin', 
'sinc', 
'single', 
'singlecomplex', 
'sinh'] 

我覺得非常方便，探索從我期望他們必須有不明物體一個方法（或屬性）應該作爲其名稱的一部分。