How to Write Loops the Pythonic Way

Like other programming languages, Python also provides a variety of ways to write loops. However, there is a unique technique to write loops in Python that is considered to be the most “Pythonic.” This looping technique is not only efficient and effective, but it is also easily readable and maintainable. In this post, we will dive deep into some common pythonic loops that are often used.

How to write a loop in python? There are various ways for writing a loop in python some common pythonic loops that developers usually prefer are:

For Loops
While Loops
List Comprehension
Generator Expressions
Nested Loops
Break and Continue Statement
Infinite Loops
Recursive Loop

Before we start to write codes for loops in Pythonic way, let me tell you that all the codes I will show in this tutorial are tested on Python 3.

For Loops

You can use a for loop in Python to iterate through sequences like lists, tuples or strings.. While iterating over, it executes some blocks of code. For example, the for loop below iterates through a list of fruits and prints each fruits names from the list one by one:

# loop over a list
fruits = ['apple', 'banana', 'mango']
for fruit in fruits:
    print(fruit)

Output:
apple
banana
mango

You can also use the range() function to achieve the same task. range() function is frequently used in daily python script development.

# loop over a list using pythonic range() function
fruits = ['apple', 'banana', 'mango']
for i in range(len(fruits)):
    print(fruits[i])

Output:
apple
banana
mango

Here in this code, we are first finding out the length of the list. Then loop through each index of the list until it’s the maximum length. Then printing the element of that list for that specific index.

We can also use enumerate() function to get the index and the value of the list or tuple.

While Loops

You can use while loops are used to repeat a block of code until a certain condition is true. A real-life example of while loop would be: Let’s say you are surfing channels on TV. Based on your mood, you will keep on surfing channels until you get a suitable channel for you. Below is an example of a while loop.

# print numbers from 0 to 4
i = 0
while i < 5:
  print(i)
  i += 1

Output:
0
1
2
3
4

In this code for each loop value of i is increasing by 1 point (the initial value of i is 0). The while loop will run until the value of i is less than 5.

List Comprehension

List comprehension is an elegant way to create a list using a single line of code in Python. It is most useful when you are working with a list and want to reduce the size of your python code. List comprehension is frequently used as a shorter alternative to a for loop.

In general, list comprehension is more compact and faster than standard functions and loops for creating lists. However, I will recommend you not use long and compact list comprehensions in one line to make our code user-friendly. Here’s an example of list comprehension in Python:

# create a list of squares
squares = [i ** 2 for i in range(5)]
print(squares)

# create a list of even numbers
evens = [i for i in range(10) if i % 2 == 0]
print(evens)

Output:
[0, 1, 4, 9, 16]
[0, 2, 4, 6, 8]

Generator Expressions

Generator expressions are similar to list comprehensions, the only difference is instead of creating a new list, they return a generator object. If the resulting list is very large, this technique can be more memory-efficient. This is because the generator generates the values one at a time as needed, instead of creating a large data structure to hold all values at once. Let’s one example of a generator in Python:

# create a generator object that generates the squares of numbers from 0 to 9
squares = (i ** 2 for i in range(10))

# print the first 5 squares
for i in range(5):
  print(next(squares))

Output:
0
1
4
9
16

Nested Loops

A nested loop is a loop inside another loop. Nested loop in Python allow you to perform operations on multiple iterable objects in one block of code. Below is an example of a Pythonic way to write a loops:

# print all combinations of fruit and color
fruits = ['apple', 'banana', 'mango']
colors = ['red', 'yellow', 'green']
for fruit in fruits:
  for color in colors:
    print(fruit, color)

Output:
apple red
apple yellow
apple green
banana red
banana yellow
banana green
mango red
mango yellow
mango green

Break and Continue Statement

You can use break statement if you want to break or exit a loop (for loop or while loop) and move on to the next block of your python code. The break statement can be useful if you are with a huge iterable object (for example iterating over a huge list) and you want to stop the for loop or while loop if you get your desired result.

Also Read: Automatic Update Google Sheet from Python

On the other hand, the continue statement can be used to skip the rest of the current iteration and move on to the next one. Let’s see some examples to clear our concept.

# print the first even number greater than 3
for i in range(10):
  if i % 2 == 1:
    continue  # skip odd numbers
  if i > 3:
    print(i)
    break  # exit the loop

Output:
4

Infinite Loops

An infinite loop is a loop that runs forever unless it is interrupted by a break statement or some other means. Infinite loops are useful for tasks that need to run continuously in the background, such as servers and other types of long-running programs. Below is an example of Pythonic way to write a infinite loops:

while True:
  # do something indefinitely
  print("Hello, world!")

Output:
Hello, world!
Hello, world!
Hello, world!
...
...
...

Recursive Loop

A recursive loop in Python is like a snake eating its own tail. It’s a never-ending cycle of function calls that just keeps calling itself over and over again until it finally reaches the end and can finally take a break!

It’s like a dog chasing its own tail, it looks cool but it doesn’t really get you anywhere. But unlike a dog, a recursive loop can be useful for solving certain types of problems, like traversing a data structure or calculating factorials. In easyer word it’s like a never-ending journey.

Here’s an example of Pythonic way to write a recursive function or loops that calculates the factorial of a given number:

def factorial(n):
    if n == 1:
        return 1
    else:
        return n * factorial(n-1)

print(factorial(5))

Output:
120

In this example, the function factorial takes an argument n and checks if it is equal to 1. If it is, it will return 1. If not, it will return n multiplied by the factorial of n-1. This function will call itself repeatedly, each time with a decreased value of n, until value of n is equal to 1.

This is it for Pythonic loops. I have tried to list down all popular loops in Python. Please let me know if I missed something to add in the comment section below.

Now let’s see some frequently asked questions about Python loops.

FAQs

Here I am listing down some frequently asked questions about Pythonic way to write a loops:

Python how to make loop faster?

There are several ways to make a loop faster in Python:

Use built-in functions and libraries: Python offers many built-in functions and libraries that are designed to perform specific tasks quickly and efficiently, try using them. For example, instead of using a loop to search for an item in a list, you can use the in operator or the index() method.
Avoid unnecessary operations: If a loop performs the same operation multiple times, it’s a good idea to move that operation outside of the loop to avoid repeating it.
Avoid creating unnecessary objects: Creating new objects inside a loop can slow down the process. Instead, try to reuse objects that are already in memory.
Use the right data types: Using the appropriate data type for a task can make a big difference in performance. For example, using a set instead of a list for searching can make the process a lot faster.
Use the right loop construct: Python provides different types of loops such as for, while and list comprehension. If the operation is simple and you need to iterate over a list, list comprehension can be faster.
Use map() and filter() functions: These functions are optimized for working with lists and can be faster than a loop.
Use itertools : Python’s itertools library has efficient functions such as combinations, permutations, etc.
Use Cython or Numba: To make further improvements, you can use Cython or Numba to convert your python code to C or machine code. These libraries can improve performance by several orders of magnitude.

Also Read: Python Replace all occurrence - Complete Guide

Does return statement break a loop python?

The return statement will not break a loop in Python. It will only exit the current function or method that it is in and return a value to the caller (or while executing). When calling a function or method within a loop, the loop will continue its execution even after the function or method returns.

However, if the return statement is used inside a loop in a function, and the condition is met, then it will break the loop and exit the function.

Here is an example:

def my_function():
    for i in range(10):
        if i == 5:
            return i
    print("I will not be executed")

print(my_function())

Output:
5

In this example, the loop will run until the condition i == 5 is met. When the condition is met, the return statement is executed, the function exits and returns the value of i, which is 5. Last print statement after the loop will not execute because it is outside of the function.

It’s also worth noting that there are other ways to break a loop in python such as using the break statement. It will immediately exit the loop, regardless of the current iteration, and continue with the next instruction after the loop.

Ways to end a loop in python

There are several ways to end a loop in Python:

break statement: The break statement is used to exit a loop early, regardless of the current iteration. When a break statement is encountered inside a loop, the loop is immediately terminated and the program continues with the next statement after the loop.
return statement: The return statement is used to exit a function or method and return a value to the caller. If a return statement is encountered inside a loop, the function or method will exit and the loop will be terminated. However, it will not break the flow of the program outside the function.
continue statement: The continue statement is used to skip an iteration of a loop and move on to the next iteration. When a continue statement is encountered inside a loop, the current iteration is skipped and the program continues with the next iteration of the loop.
else statement : The else statement is used with loops, it specifies a block of code to be executed when the loop is finished. The program will execute it only if the loop completes its execution normally, meaning it does not encounter a break statement..
Using a flag variable: You can also use a flag variable to control the flow of the loop. Set the flag variable to a specific value before starting the loop, and then check the value of the flag inside the loop. If the value of the flag meets a certain condition, you can use the break statement to exit the loop.
Using the sys module: Python’s sys module provides an exit() function which can be used to exit a script or program.

Also Read: Replace Text in a PDF File with Python

How to loop a sentence in Python?

There are several ways to loop through a sentence in Python: for loop, while loop, enumerate() function, List comprehension, etc. Let’s see some examples to loop a sentence in Python.

# Using for loop
print('Using for loop----')
sentence = "Hello, World!"
for char in sentence:
    print(char)
    
# Using while loop
print('Using while loop----')
sentence = "Hello, World!"
i = 0
while i < len(sentence):
    print(sentence[i])
    i += 1
    
# Using enumerate() function
print('Using enumerate() function----')
sentence = "Hello, World!"
for index, char in enumerate(sentence):
    print(f"{index}: {char}")
    
# Using List comprehension
print('Using List comprehension----')
sentence = "Hello, World!"
[print(char) for char in sentence]

Output:
Using for loop----
H
e
l
l
o
,
 
W
o
r
l
d
!
Using while loop----
H
e
l
l
o
,
 
W
o
r
l
d
!
Using enumerate() function----
0: H
1: e
2: l
3: l
4: o
5: ,
6:  
7: W
8: o
9: r
10: l
11: d
12: !
Using List comprehension----
H
e
l
l
o
,
 
W
o
r
l
d
!

How to create variables in a loop?

You can create variables inside a loop in Python using the = operator, just like you do outside of a loop normally. Here are a few examples:

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

This will create a variable variable_i for each iteration of the loop, and assigns the current value of i to it.

my_list = [1, 2, 3, 4, 5]
for item in my_list:
    variable_item = item
    print(variable_item)

This will create a variable variable_item for each iteration of the loop, and assigns the current value of item to it.

Also, if you want to create variables with a specific naming convention, such as var1, var2, var3, etc. you can use string formatting. Here’s an example:

for i in range(5):
    variable_name = "var{}".format(i)
    print(variable_name)

This will create variable names var0, var1, var2, var3, var4.

How to write a fixed loop in python?

A fixed loop in Python is a loop that runs a fixed number of times. There are several ways to write a fixed loop in Python, such as using a for loop with the range() function or a while loop with a counter variable.

All of the examples I showed you in this post that are fixed loops, except the infinite loop.

How to write a decreasing for loop in python

To make a loop countdown in python, you can use the range() function with three arguments (start, stop, and step). The loop will iterate from the start value to the stop value in decrement steps.

start is the initial value
stop is the final value
step is the decrement value

for i in range(10, 0, -1):
    print(i)

Output:
10
9
8
7
6
5
4
3
2
1

Another way to create a decreasing loop is by using reversed() function:

for i in reversed(range(1,11)):
    print(i)

This will also print the numbers from 10 to 1 in a decreasing manner.

You can also use while loop and decrement the value of the iterator in each iteration.

i = 10
while i>0:
    print(i)
    i-=1

Anindya

Hi there, I’m Anindya Naskar, Data Science Engineer. I created this website to show you what I believe is the best possible way to get your start in the field of Data Science.