Conditionally replace values in a Python list

This post will discuss how to conditionally replace values in a list in Python.

1. Using List Comprehension

The most Pythonic solution is to use a list comprehension, which can construct a new list whose each element results from some operation applied to each member of an iterable.

Here’s a working example where each odd element in the list is replaced by value 0:

if __name__ == '__main__':

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

a = [0 if x % 2 == 1 else x for x in a]

print(a) # prints [0, 2, 0, 4, 0, 6, 0, 8, 0]

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2. Using `enumerate()` function

You can also use the enumerate() function to retrieve the position index and corresponding value at the same time while looping through a list.

Here’s a working example where we have used the value to check for odd element and its index to update the value if required:

if __name__ == '__main__':

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

for i, v in enumerate(a):

if v % 2 == 1: # odd indices

a[i] = 0

print(a) # prints [0, 2, 0, 4, 0, 6, 0, 8, 0]

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3. Using `map()` function

This can also be done using Python’s built-in function map() and lambda expression. Note that map() is obsolete and considered unpythonic as it duplicates the features of generator expressions.

if __name__ == '__main__':

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

a = list(map(lambda x: 0 if x % 2 == 1 else x, a))

print(a) # prints [0, 2, 0, 4, 0, 6, 0, 8, 0]

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That’s all about conditionally replace values in a list in Python.

Conditionally replace values in a Python list

1. Using List Comprehension

2. Using enumerate() function

3. Using map() function

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2. Using `enumerate()` function

3. Using `map()` function