Python Lists

A list in python is a compound data type which can store multiple elements.

• Items of a list are enclosed within square brackets ([])
• Items are separated by commas
• The items of a list can be of different data type.
  Ex: l1 = [1,2,”a”,2.3,3j]
• Slice operator ([ ] and [:] ) can be used to access elements in a list. Negative index: count from the right. Ex: print(l1[-2]) returns 2.3
• Indexes start at 0
• Concatenation operator: plus (+) sign. Ex: [1, 2, 3] + [4, 5, 6]returns [1, 2, 3, 4, 5, 6]
• Repetition operator: asterisk (*). Ex: [‘Hi!’] * 4 returns [‘Hi!’, ‘Hi!’, ‘Hi!’, ‘Hi!’]
• len(list) returns the number of elements in the list. Ex: len([1, 2, 3]) returns 3
• in operator returns the membership of an element in a list. Ex: 3 in [1, 2, 3] returns True

l1 = [1,2,"a",2.3,3j]
l2 = [567, "jonny"]
print(l1)          # Prints all the elements of list
print(l1[0])       # Prints 1st elements of the list
print(l1[1:3])     # Prints elements from 2nd till 3rd 
print(l1[2:])      # Prints all the elements of l1 from 3rd value
print(l2 * 2)      # Prints list l2 twice
print(l1 + l2)     # Prints concatenated lists
l1[2]=3            # Updates 3rd element of the list
print(l1[2])       # Prints updated 3rd element of the list
del l1[2]          # Deleting 3rd element of the list
print(l1) 

OUTPUT:

[1, 2, 'a', 2.3, 3j]
1
[2, 'a']
['a', 2.3, 3j]
[567, 'jonny', 567, 'jonny']
[1, 2, 'a', 2.3, 3j, 567, 'jonny']
3
[1, 2, 2.3, 3j, 567, 'jonny']

Built-in List Functions & Methods:

Functions defined for lists in python:

Methods	Returns	Description/Example
cmp(list1, list2)	if (x ((x-y)<0) returns -1 if (x==y) => ((x-y)==0) returns 0 if (x>y) => ((x-y)>0) returns 1	Compares list1 with list2
len(list)	Number of elements of the list	len([1, 2, 3]) returns 3
max(list)	Item with max value	max([1, 2, 3]) returns 3
min(list)	Item with min value	min([1, 2, 3]) returns 1
append(obj)	It returns nothing. Appends object obj to list	l1=[1,2,3]; l1.append([4,5]) print(l1) prints [1,2,3,4,5]
count(obj)	Returns count of how many times obj occurs in list	l1=[1,2,3,2]; l1.count(2) returns 2
extend(seq)	It returns nothing. Appends the contents of seq to list	l1=[1,2,3]; l1.extend([4,5]); print(l1) prints [1,2,3,4,5]
index(obj)	Returns the first index where obj is found in list	l1=[1,2,3,2]; l1.index(2) prints 1
insert(index, obj)	It returns nothing. Inserts object obj into list at offset index	l1=[1,2,3]; l1.insert(4,1); print(l1) prints [1,4,2,3]
pop(index)	Removes and return object from index. If no index is passed, removes and returns the last item	l1=[1,2,3,2]; l1.pop(1); print(l1) prints 2 [1,3,2]
remove(obj)	It returns nothing. Remove the first item from the list whose value is obj.	l1=[1,2,3,2]; l1.remove(2); print(l1) prints [1,3,2]
reverse()	Returns nothing. Reverses objects of list in place	l1=[1,2,3,2]; l1.reverse(); print(l1) prints [2,3,2,1]
sort()	Returns nothing. Sorts objects of list	l1=[1,2,3,2]; l1.sort(); print(l1) prints [1,2,2,3]

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