One Line for Loop in Python

  1. Simple One Line for Loop in Python
  2. List Comprehension in Python Using the One Line for Loop
  3. List Comprehension in Python With if...else Statement Using the One Line for Loop

This tutorial will explain various methods to implement one-line for loop in Python. There are different forms of one-line for loop in Python; one can be a simple for loop that iterates through an iterable object or a sequence. The other can be simple list comprehension and list comprehension with if...else statement.

Simple One Line for Loop in Python

The simple one-line for loop is the for loop, which iterates through a sequence or an iterable object. Therefore we can either use an iterable object with the for loop or the range() function. The iterable object can be a list, array, set, or dictionary.

The below example code demonstrates how to implement one-line for loop to iterate through Python’s iterable object.

myset = {'a','b','c','d','e','f','g'}
mydict = {'a':1,'b':2,'c':3,'d':4,'e':5,'f':6,'g':7}

for x in myset:
    print(x)

for key, val in mydict.items():
    print(key,val)

The range(start, stop, step) function returns a sequence starting from the start value and ending at the stop value with the step size equal to the step.

The below example code demonstrates how to use the range() function to implement one-line for loop in Python.

for x in range(1,99):
    #do something

List Comprehension in Python Using the One Line for Loop

List comprehension is a syntactic way to create a new list from an existing list in many programming languages, including Python. We can apply any operation on each element of the list and create a new list using simple list comprehension.

The below example code demonstrates how to implement the list comprehension using the one-line for loop in Python. The below code creates a new list by taking the square of each element of the existing list.

mylist = [6,2,8,3,1]

newlist = [x**2 for x in mylist]
print(newlist)

Output:

[36, 4, 64, 9, 1]

List Comprehension in Python With if...else Statement Using the One Line for Loop

List comprehension with if...else statement is used to apply operations on some specific elements of the existing list to create a new list or filter elements from the existing list to create a new one.

The following example codes demonstrate how to implement the list comprehension with the if statement and with the if..else statement in Python using the one-line for loop.

The below example code adds the elements to the new list if it is an odd number and discards it if it is an even number.

mylist = [1,4,5,8,9,11,13,12]

newlist = [x for x in mylist if x%2 == 1]
print(newlist)

Output:

[1, 5, 9, 11, 13]

The below example code using the one line if...else list comprehension converts an odd element to an even by adding 1 to it and adds even elements to the list without performing any operation on them, and as a result, we get a new list of even numbers.

mylist = [1,4,5,8,9,11,13,12]

newlist = [x+1 if x%2 == 1 else x for x in mylist]
print(newlist)

Output:

[2, 4, 6, 8, 10, 12, 14, 12]
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