List Comprehensions

It is very easy and compact way of creating list objects from any iterable objects (like list, tuple, dictionary, range etc.) based on some condition.

Syntax

Python

my_list=[expression for item in list if condition]

Example

Python

s=[ x*x for x in range(1,11)]
print(s)
v=[2**x for x in range(1,6)]
print(v)
m=[x for x in s if x%2==0]
print(m)

Output

PowerShell

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
[2, 4, 8, 16, 32]
[4, 16, 36, 64, 100]

Example

Python

words=["Balaiah","Nag","Venkatesh","Chiranjeevi"]
l=[w[0] for w in words]
print(l

Output

PowerShell

['B', 'N', 'V', 'C']

Example

Python

num1=[10,20,30,40]
num2=[30,40,50,60]
num3=[ i for i in num1 if i not in num2]
print(num3)

num4=[i for i in num1 if i in num2]
print(num4)

Output

PowerShell

[10, 20]
[30, 40]

Example

Python

words="the quick brown fox jumps over the lazy dog".split()
print(words)
l=[[w.upper(),len(w)] for w in words]
print(l)

Output

PowerShell

['the', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog']
[['THE', 3], ['QUICK', 5], ['BROWN', 5], ['FOX', 3], ['JUMPS', 5], ['OVER', 4], ['THE', 3], ['LAZY', 4], ['DOG', 3]]

Question

Write a program to display unique vowels present in the given word?

Python

vowels=['a','e','i','o','u']
word=input("Enter the word to search for vowels: ")
found=[]
for letter in word:
  if letter in vowels:
    if letter not in found:
      found.append(letter) 
print(found)
print("The number of different vowels present in",word,"is",len(found))

Output

PowerShell

Enter the word to search for vowels: internetknowledgehub
['i', 'e', 'o', 'u']
The number of different vowels present in internetknowledgehub is 4

Nested Lists

Sometimes we can take one list inside another list. Such type of lists are called nested lists.

Example

Python

n=[10,20,[30,40]]
print(n)
print(n[0])
print(n[2])
print(n[2][0])
print(n[2][1])

Output

PowerShell

[10, 20, [30, 40]]
10
[30, 40]
30
40

Note

We can access nested list elements by using index just like accessing multi dimensional array elements.

Nested List as Matrix

In Python we can represent matrix by using nested lists.

Example

Python

n=[[10,20,30],[40,50,60],[70,80,90]]
print(n)
print("Elements by Row wise:")
for r in n:
  print(r)
print("Elements by Matrix style:")
for i in range(len(n)):
  for j in range(len(n[i])):
    print(n[i][j],end=' ')
  print()

Output

PowerShell

[[10, 20, 30], [40, 50, 60], [70, 80, 90]]
Elements by Row wise:
[10, 20, 30]
[40, 50, 60]
[70, 80, 90]
Elements by Matrix style:
10 20 30 
40 50 60 
70 80 90

Ungraded Questions

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