Python List Comprehensions
List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.
Syntax
newlist = [expression for item in iterable if condition == True]The return value is a new list, leaving the old list unchanged.
Examples
Basic Iteration
Instead of using a for loop:
fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = []
for x in fruits:
if "a" in x:
newlist.append(x)
print(newlist)You can do this in one line:
fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = [x for x in fruits if "a" in x]
print(newlist)Condition
The condition is like a filter that only accepts the items that valuate to True.
newlist = [x for x in fruits if x != "apple"]Expression
The expression is the current item in the iteration, but it is also the outcome, which you can manipulate before it ends up like a list item in the new list:
newlist = [x.upper() for x in fruits]