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List in Python

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June 21, 2017
Published By : Pratik Kataria
Categorised in:

  • List in Python is like ArrayList in Java.
  • The elements are addressed by index which starts from 0.
  • The list may contain elements of different data types unlike arrays in C or C++.
  • Python has lots of in-built functionalities when it comes to list:
    • cmp(list1, list2)
    • len(list)
    • max(list)
    • min(list)
    • list(sequence) – tuples are converted into a list
  • Let’s see rest of the functions of list in python in action.

Note: This is Command Line Python

>>> a_list = []
>>> a_list
[]
>>> a_list = ["something",234]
>>> a_list
['something', 234]
>>> a_list[0]
'something'
>>> a_list.count(234)
1
>>> a_list.append(334)
>>> a_list
['something', 234, 334]
>>> a_list.append(234)
>>> a_list
['something', 234, 334, 234]
>>> a_list.index(234)
1
>>> a_list.insert(1,"some string")
>>> a_list
['something', 'some string', 234, 334, 234]
>>> a_list.pop(234)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: pop index out of range
>>> a_list.pop(1)
'some string'
>>> a_list
['something', 234, 334, 234]
>>> a_list.remove(234)
>>> a_list
['something', 334, 234]
>>> a_list.reverse()
>>> a_list
[234, 334, 'something']
>>> a_list.sort()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '<' not supported between instances of 'str' and 'int'
>>> another_list= [10,9,8,7]
>>> another_list
[10, 9, 8, 7]
>>> another_list.sort()
>>> another_list
[7, 8, 9, 10]
>>> sorted(another_list, reverse=True)
[10, 9, 8, 7]
>>> another_list
[7, 8, 9, 10]
  • By default, sort() does not require extra parameters. However, it has two (optional) parameters:
    • reverse – if true then list is sorted in descending order
    • key – a function that tells sort function the key for sort comparison
  • sort() method doesn’t return. It makes changes to original list.
  • If you want to keep original list intact then use sorted:
    • sorted(a_list,  key=…,  reverse=…)