Syntax of built in methods in Python

Question

so there is a string, lets say a='abc' and two built in string methods for that string object (and string class in general):

len(a)
a.capitalize()

So when is first syntax, method(object), used over the second, object.method() ?

Thanks a lot

Answer 1

The first function is a built-in function that is not associated with any class. You can view a list of all builtins available to you using dir(__builtins__):

>>> dir(__builtins__)
'ArithmeticError', 'AssertionError', ...  'len', ... 'vars', 'zip']

len() is designed to return the size of any iterable, not just a string.

The second function is actually a method of the builtin class str. You can peruse the methods of str with dir(str), and confirm capitalize is an instance method of str.

>>> 'capitalize' in dir(str)
True

Instance methods are invoked on the instances of the object, such as 'abc'.capitalize(). This means that the call passes abc as an invisible argument to capitalize. Methods are meant to work only on instances of that class type.