Different built-in functions in Python

Question

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?

Answer 1

Some context:

each_item.isalpha() is not a built-in function as such. It is a method of the "str" class.

Whereas "sum" is a built-in function, a globally known name which can be accessed and used without explicitly importing any module.

There's an explicit list of the built-in functions in the Python doco.

For a class, you can look at the doco for the class ("String methods" in the python doco, for the "str" class), or run:

help(str)

at the interactive Python prompt.

Answer 2

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.