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From: Ned Batchelder <ned@nedbatchelder.com>
Subject: Re: confused about the different built-in functions in Python
Date: Sun, 25 May 2014 22:12:19 -0400
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Xref: csiph.com comp.lang.python:72043

On 5/25/14 7:55 PM, Deb Wyatt wrote:
> I am confused about how various built-in functions are called.  Some are
> called with dot notation
>
> each_item.isalpha()
>
> and some are called like 'normal'
>
> sum(numlist)
>
> How do you know/remember which way to call them?
>
> TIA,
> Deb in WA, USA

It can be confusing.  Generally, built-in functions (like sum, len, etc) 
are used when the operation could apply to many different types.  For 
example, sum() can be used with any iterable that produces addable things.

Operations that are defined only for a single type (like .isalpha as a 
string operation) are usually defined as methods on the type.

This is not a black/white distinction, I'm sure there are interesting 
counter-examples.  But this is the general principle.

-- 
Ned Batchelder, http://nedbatchelder.com