Table of Contents

• 1  Loops

  • 1.1  For

  • 1.2  While

• 2  Break

• 3  Continue

• 4  List Comprehensions

Loop

import os
from IPython.core.display import HTML
def load_style(directory = '../', name='customMac.css'):
        styles = open(os.path.join(directory, name), 'r').read()
        return HTML(styles)
load_style()

Loops

For

for variable in something:

algorithm

for i in range(5):
    print(i)

0
1
2
3
4

In the above example, i iterates over the 0,1,2,3,4. Every time it takes each value and executes the algorithm inside the loop. It is also possible to iterate over a nested list illustrated below.

list_of_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for list1 in list_of_lists:
        print(list1)

[1, 2, 3]
[4, 5, 6]
[7, 8, 9]

A use case of a nested for loop in this case would be,

list_of_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for list1 in list_of_lists:
    for x in list1:
        print(x)

1
2
3
4
5
6
7
8
9

While

while some_condition:

algorithm

i = 1
while i < 3:
    print(i ** 2)
    i = i+1
print('Bye')

1
4
Bye

Break

As the name says. It is used to break out of a loop when a condition becomes true when executing the loop.

for i in range(100):
    print(i)
    if i>=7:
        break

0
1
2
3
4
5
6
7

Continue

This continues the rest of the loop. Sometimes when a condition is satisfied there are chances of the loop getting terminated. This can be avoided using continue statement.

for i in range(10):
    if i>4:
        print("The end.")
        continue
    elif i<7:
        print(i)

0
1
2
3
4
The end.
The end.
The end.
The end.
The end.

List Comprehensions

Python makes it simple to generate a required list with a single line of code using list comprehensions. For example If i need to generate multiples of say 27 I write the code using for loop as,

res = []
for i in range(1,11):
    x = 27*i
    res.append(x)
print(res)

[27, 54, 81, 108, 135, 162, 189, 216, 243, 270]

Since you are generating another list altogether and that is what is required, List comprehensions is a more efficient way to solve this problem.

[2*x for x in range(1,11)]

[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

That’s it!. Only remember to enclose it in square brackets

Understanding the code, The first bit of the code is always the algorithm and then leave a space and then write the necessary loop. But you might be wondering can nested loops be extended to list comprehensions? Yes you can.

[2*x for x in range(1,20) if x<=10]

[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

Let me add one more loop to make you understand better,

[2*z for i in range(50) if i==6 for z in range(1,11)]

[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]