List comprehensions in python

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list_comprehension

Skill - List Comprehensions in python

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Skills Required

Please make sure to have all the skills mentioned above to understand and execute the code mentioned below. Go through the above skills if necessary for reference or revision

List Comprehension can be used to create a list from another list/sequence in a user-friendly way and with less lines of code.
Generally people use list comprehensions write simple for loops in a single line
All List comprehensions can be replaced by a for loop.
But all for loops can’t be replaced by List comprehensions.

Creating list from another sequence/list using list comprehension

list_comprehension_illustration

  • As shown in the above image, for creating a new list we require the input list, operation on each list item, conditional statement for including the list item if any.
  • The conditional statement can be used as a filter to exclude undesired list items from the output list

Creating a list of 15 numbers using ‘List Comprehension’

lst = [t for t in range(15)]

print(lst)
# This will print
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

Creating a list of 15 numbers using ‘for’ loop

lst = []

for t in range(15):
	lst.append(t)

print(lst)
# This will print
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

You can see from the above two examples that list comprehension is more user friendly to write and uses less lines of code

Converting all strings in list to uppercase

cities = ['Mumbai', 'Delhi', 'Bangalore ', 'Hyderabad',
          'Ahmedabad', 'Chennai', 'Kolkata',
          'Surat', 'Pune']

lst = [x.upper() for x in cities]

print(lst)

Using the conditional statement as filter in list comprehension

In this example we will generate even numbers using list comprehension

lst = [x for x in range(0,17) if x%2==0]

print(lst)
# this will print
# [0, 2, 4, 6, 8, 10, 12, 14, 16]

Video

Video for this post can be found here

Online Interpreter

You can run these codes online at https://www.programiz.com/python-programming/online-compiler/

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