Looping Techniques in Python

In this short tutorial, you will learn how to use loops more effectively in different situations.
 

Looping over two lists at the same time.

You might want to iterate/loop over two lists or sequences at the same time.

This can be achieved using the zip() function.

colors = ["red", "blue", "white"]
types = ["warm", "cool", "neutral"]

for c, t in zip(colors, types):
    print(c + " is " + t)

Program Output:

red is warm
blue is cool
white is neutral

 

 

The enumerate() function.

When looping through a sequence (lists, tuple, string, etc), the position index and corresponding value can be retrieved at the same time using the enumerate() function.

colors = ["orange", "brown", "indigo", "black"]

for i, v in enumerate(colors):
    print(i , v)

Program Output:

0 orange
1 brown
2 indigo
3 black

 

The enumerate() function returns individual elements in the list with their indexes.

 

 

Looping through a dictionary with the items() method.
 

We can get both the keys and the corresponding values when looping over a dictionary by using the items() method.

grades = {'Ana': 'B', 'John':'A+', 'Denise':"A", "katy": 'A'}

for name, g in grades.items():
    print(name + " had " + g)

Program Output:

Ana had B
John had A+
Denise had A
katy had A

 

 

Reverse looping.

To loop over a range of numbers in reverse, first, specify the range and then call the reversed() function.

for r in reversed(range(7)):
    print(r)

Program Output:

6
5
4
3
2
1
0

 

The same analogy applies to looping over a list in reverse:

colors = ["blue", "red", "black", "yellow"]

for i in reversed(colors):
    print(i)

Program Output:

yellow
black
red
blue

 

 

 

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