reading-notes

Game of Greed Reading Part 3

List Comprehensions in Python

List comprehension is a powerful and concise method for creating lists in Python that becomes essential the more you work with lists, and lists of lists.

List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.

Syntax

my_new_list = [ expression for item in list ]

there are three parts in the expression above which are :

1. the expression we’d like to carry out. expression inside the square brackets.
2. the object that the expression will work on. item inside the square brackets.
3. an iterable list of objects to build our new list from. list inside the square brackets.

Example for Creating a List Using Loops and List Comprehension in Python

fruits = ["apple", "banana", "cherry", "kiwi", "mango"]

newlist = [x for x in fruits if "a" in x]

Example for condinditions in list comprehension

newlist = [x for x in fruits if x != "apple"]

in the example above, The condition if x != “apple” will return True for all elements other than “apple”

Example for Multiplying Parts of a List

multiples_of_three = [ x*3 for x in range(10) ]

Example for showing the first letter of each word using Python

letters = [ name[0] for name in authors ]

where authors is a list of strings .

Example for Lower/Upper case converter using Python

lower_case = [ letter.lower() for letter in ['A','B','C'] ]

upper_case = [ letter.upper() for letter in ['a','b','c'] ]

Example for Printing numbers only from a given string

user_data = "Elvis Presley 987-654-3210"

phone_number = [ x for x in user_data if x.isdigit()]

isdigit() is a python built-in method that checks if the string character is a digit or not

Summary

• List comprehension is an elegant way to define and create lists based on existing lists, it’s easier than the normal way
• List comprehension is generally faster than normal functions and loops for creating list.
• we should avoid writing very long list comprehensions in one line to ensure that code is user-friendly.
• every list comprehension can be rewritten in for loop, but every for loop can’t be rewritten in the form of list comprehension.

for more understanding of list comprehension in Python:

• for loop in list comprehension:

  

• for loop with if condition: