how to show all the methods to a particular class, or functions such as **kwargs?

Question

i tried help(**kwargs), and help(kwargs) but received an error.

There are online sites that show you all available methods for a dictionary, but none for something not so newbie friendly like kwargs.

I am asking for a generic method to find built in python info so that I don't have to ask those questions online. Thanks.

Edit_1, for example, I saw this from someone else's code:

def somefunction(**kwargs):
    for key, value in kwargs.item():
        print key, value

How do I find out more methods like the above example, item() ?

Answer 1

kwargs is just a name and ** is use to unpack dictionaries (kew words argument )

NB: kwargs could be any name you like

Little bit about kwargs:

>>> def foo(**new_kwargs):
...     print new_kwargs
...
>>> dic = { 'key' : 'value' }    
>>> foo(**dic)
{'key': 'value'}
>>>
>>> foo(key='value')
{'key': 'value'}
>>>
>>> foo(dic)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: foo() takes exactly 0 arguments (1 given)
>>>

And :

If you want to see all the attributes and method for a particular object (even class is an object in python): Use dir built-in function:

dir(...)
    dir([object]) -> list of strings

And if you want to see any particular attributes is method or function, you can use callable to check if they are callable:

>>> dir(dict)
['__class__', '__cmp__', '__contains__', '__delattr__', '__delitem__', '__doc__',
 '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__',
 '__hash__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__',
 '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setitem__', '__sizeof__',    
 '__str__', '__subclasshook__', 'clear', 'copy', 'fromkeys', 'get', 'has_key', 'items',
 'iteritems', 'iterkeys', 'itervalues', 'keys', 'pop', 'popitem', 'setdefault',    
 'update', 'values', 'viewitems', 'viewkeys', 'viewvalues']
>>>

>>> callable(dict.keys)
True
>>>   


>>> class foo(object):
...     class_variable = 'Some String'
...     def function():
...         return 'Some String'
...
>>> dir(foo)
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__',
 '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', 
'__repr__',     '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 
'__weakref__', 'class_variable', 'function']
>>>
>>> callable(foo.class_variable)
False
>>> callable(foo.function)
True
>>>

What ever you show extra in dir(foo) are from base class object.

Answer 2

*kwargs just means that a method takes multiple keyword arguments that aren't defined.

Take this example:

def foo(a,b,c=10,**kwargs):
    pass

This method has two required positional arguments, one argument c that is optional (since it has a default value), and then takes any number of additional arguments. All these are valid calls:

foo(1,2,hello='world',bar='baz')
foo(1,2,3,hello='world',bar='baz',zoo='foo')

Since they are variable, there is nowhere to list them.

The best you can do is use the built-in help() function and hope that the programmer has written some docstrings to highlight the use of the function you are interested in:

def foo(a,b,c=10,**kwargs):
    '''This function takes extra arguments
       that can be used to calculate the
       meaning of life. The first two arguments
       a and b are required, c is set to 10 as
       a default.

       Examples:
           foo(1,2,hal='are you there?')'''

Now, when you do help(foo) it will print out that string.

dir() is another built-in that is useful. It returns a list of attributes for the passed in object, or a list of names (variables) that are available in the current scope.

If you want to know what all things you can do with an object (basically, what goes after the .), type dir(theobject). For example, dir({}) will list all the attributes of a dictionary.

Answer 3

If you are looking for documentation of builtin module,this link might help: http://effbot.org/librarybook/builtin.htm. Your question is not specific, it would be great if you add more details.