Suppose we need to create a list with first 10 multiple of 6 in it, So we may do this with a normal
for loop or with list comprehensions, Let's see both of them and understand the difference.
Normal For loop
list1 =[]
for n in range(1,11):
list1.append(n*6)
print(list1)
Output:
[6, 12, 18, 24, 30, 36, 42, 48, 54, 60]
List comprehension
list1 = [n*6 for n in range(1,11)]
print(list1)
Output:
[6, 12, 18, 24, 30, 36, 42, 48, 54, 60]
We got the same output using list comprehensions just by writing a line of code.
In general list comprehension
[<the_expression> for <the_element> in <the_iterable>]
Comparing this with our example n*6 is the expression, n is the element, range(1,11) is the
iterable.
Applying list comprehension with a condition
Now, Suppose we need to create a list of multiple of 6 for just even numbers between 1 to 10.
list1 =[]
for n in range(1,11):
if n%2==0:
list1.append(n*6)
print(list1)
Output:
[12, 24, 36, 48, 60]
Using list comprehensions
list1 = [n*6 for n in range(1,11) if n%2==0]
print(list1)
Output:
[12, 24, 36, 48, 60]
In general list comprehension
[<the_expression> for <the_element> in <the_iterable> if <the_condition>]
Comparing this with our example n*6 is the expression, n is the element, range(1,11) is the
iterable and n%2==0 is the condition.
Applying list comprehension with if-else condition
Now, Suppose we need to create a list of multiple of 6 for even numbers between 1 to 10 and
multiple of 5 for rest of the numbers.
list1 =[]
for n in range(1,11):
if n%2==0:
list1.append(n*6)
else:
list1.append(n*5)
print(list1)
Output:
[5, 12, 15, 24, 25, 36, 35, 48, 45, 60]
Using list comprehensions
list1 = [n*6 if n%2==0 else n*5 for n in range(1,11)]
print(list1)
Output:
[5, 12, 15, 24, 25, 36, 35, 48, 45, 60]
In general list comprehension
[<the_expression> if <the_condition> else <other_expression> for <the_element> in
<the_iterable>]
Comparing this with our example n*6 is the expression, n%2==0 is the condition, n*5 is the
other expression, n is the element and range(1,11) is the iterable.
Applying list comprehension with Nested loops
Now, Suppose we need to multiply n ranging from 1 to 10 with first 1 then 2 and then 3.
list1 =[]
for i in range(1,4):
for j in range(1,11):
list1.append(i*j)
print(list1)
Output:
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30]
list1 = [i*j for i in range(1,4) for j in range(1,11) ]
print(list1)
Output:
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30]
In general list comprehension
[ <the_expression> for <element_a> in <iterable_a> (optional if <condition_a>)
for <element_b> in <iterable_b> (optional if <condition_b>)
for <element_c> in <iterable_c> (optional if <condition_c>)
... and so on ...]
Comparing this with our example i*j is the expression, i is the element_a, j is the element_b,
range(1,4) is the iterable_a and range(1,11) is the iterable_b.
