Python Chapter#8: Python Lists

Ankur Kulhari

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,&amp;quot;a&amp;quot;,2.3,3j]
l2 = [567, &amp;quot;jonny&amp;quot;]
print(l1)          # Prints all the elements of list
print(l1)       # 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=3            # Updates 3rd element of the list
print(l1)       # Prints updated 3rd element of the list
del l1          # 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]