In this section, we introduce lists – the most frequently used container datatype in Python. With lists, we can refer to several, even totally different, Python objects together.
A list is, as the name hints, a list of objects of any kind:
L = ['a', 20.0, 5] M = [3,['a', -3.0, 5]]
The first list in this example contains a string, a float, and an integer object. The second list in this example, M, contains another list as its second item.
The individual objects are enumerated by assigning each element an index. The first element in the list gets index 
. This zero-based indexing is frequently used in mathematical notation. Consider as an example for zero-based indexing the usual indexing of coefficients of a polynomial.
The index allows us to access the following objects from the two lists defined in the preceding example:
L[1] # returns 20.0 L[0] # returns 'a' M[1] # returns ['a',-3.0,5] M...
