functions vs methods

Sharan Basappa sharan.basappa at gmail.com
Sun Jul 22 04:37:51 EDT 2018


On Sunday, 22 July 2018 13:32:16 UTC+5:30, Ben Finney  wrote:
> Sharan Basappa <sharan.basappa at gmail.com> writes:
> 
> > Is there a difference between functions and methods in Python.
> 
> Python's documentation includes a useful Glossary. See the terms
> <URL:https://docs.python.org/3/glossary.html#term-method>
> <URL:https://docs.python.org/3/glossary.html#term-function>.
> 
> Every method is a function; but there are functions that are not
> methods.
> 
> What distinguishes a method is that it is associated with a specific
> class. A method is always a method *of* some class or object.
> 
> > For example, this is the text from tutorialpoint on Python:
> > Python includes the following list functions - cmp, len etc.
> 
> The functions ‘cmp’, ‘len’, are not associated with any particular
> class. They can be called without being bound to any object.
> 
> > Python includes following list methods - append, count
> 
> That means the functions it is referring to are each methods of ‘list’.
> Any instance of ‘list’ has methods ‘append’ and ‘count’, bound to that
> instance.
> 
> > In the first case, len is a function that python provides to which
> > list can be passed and in the second case, append is a method within
> > list class?
> 
> Yes, that's correct.
> 
> > If my interpretation is correct, why not make len also as a part of
> > list class itself?
> 
> Because ‘len’ works with *any* sequence, not only lists. To implement it
> as a method of each sequence type, it would have to be implemented on
> each type separately, which is a design that is needlessly more complex.
> 
> This is common in Python: it uses so-called “duck typing”, where the way
> an object behaves is more important than its type. Because “what is the
> length of this object” is a question valid for a broad variety of types,
> the design decision was made to allow it to accept any type for which
> that query makes sense.
> 
> <URL:https://docs.python.org/3/glossary.html#term-duck-typing>
> 
> Your particular question is itself a FAQ
> <URL:https://docs.python.org/3/faq/design.html#why-does-python-use-methods-for-some-functionality-e-g-list-index-but-functions-for-other-e-g-len-list>.
> 
> -- 
>  \           “All progress has resulted from people who took unpopular |
>   `\                                      positions.” —Adlai Stevenson |
> _o__)                                                                  |
> Ben Finney

Thanks, Ben


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