3.1.3 Lists

Python has many composite data types for grouping with other values. The most common is the list, which can be written as a list of comma-separated values (items) in square brackets. A list can contain different types of items, but usually, all items have the same type.

>>> squares = [1, 4, 9, 16, 25]

>>> squares

[1, 4, 9, 16, 25]

Like strings (and all other created -in  sequence  types), lists can be indexed and sliced:

>>> squares[0]  # indexing returns the item

1 >>> squares[-1]

25

>>> squares[-3:]

[9, 16, 25]

# slicing returns a new list

All clipping operations return a new list containing the requested items. This means that the next slice will return a new (shallow) copy of the list:

>>> squares[:]

[1, 4, 9, 16, 25]

Lists also support operations like concatenation:

>>> squares + [36, 49, 64, 81, 100]

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100. ]

Unlіkе immutable strings, the lists are of variable type, that is to say it is possible to change their content:

>>> cubes = [1, 8, 27, 65, 125]  # something's went wrong here  >>> 4 ** 3  # the cube of 4 is 64, not 65!  64

>>> cubes[3] = 64  # replace the wrong value

>>> cubes

[1, 8, 27, 64, 125]

You can also add new items to the end of the list using the append() method (we'll see more information about the method later):

>>> cubes.append(216)#Add 6 cubes

>>> cubes.append(7 ** 3)# and 7 cubes

>>>Block

[1, 8, 27, 64, 125, 216, 343]

It can also be assigned to a segment, which can even change the size of the list or remove it completely:

>>>Alphabet = ['a','b','c','d','e','f','g']

>>> letters

['a','b','c','d','e','f','g']

>>> # replace some values

>>> letters[2:5] = ['C', 'D', 'E']

>>> letters

['a', 'b', 'C', 'D', 'E', 'f', 'g']

>>> # now remove them  >>> letters[2:5] = []

>>> letters

['a', 'b', 'f', 'g']

clear the list  Replacing all elements with an empty list   >>> letters[:] = []

>>> letters

[]

The built-in function () also applies to lists:

>>> letters = ['a', 'b', 'c', 'd']

>>> len(letters)

4

It is possible to nest lists (build lists containing other lists), for example:

3.1.

>>> a = ['a', 'b', 'c']

>>> n = [1, 2, 3]

>>> x = [a, n]

>>> x

[['a', 'b', 'c'], [1, 2, 3]]

>>> x[0]

['a', 'b', 'c']

>>> x[0][1] 'b'