List in Python

• 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=…)