How to Use if-else Logic in Python List Comprehension?

Utilizing if-else Statements in List Comprehension

In Python, list comprehension provides a concise way to modify and filter list elements. One common challenge encountered is implementing an if-else logic within this construct. This article explores how to overcome this obstacle.

The Syntax Error

When attempting to use the if-else syntax in a list comprehension as follows:

[x+1 for x in l if x >= 45 else x+5]

you may encounter a syntax error. This is because the standard Python syntax for if-else statements requires the use of the if and else keywords followed by the corresponding code blocks.

The Correct Approach

To achieve an if-else like behavior in a list comprehension, you can use the conditional expression syntax:

[expression_if_true if condition else expression_if_false for x in l]

Example:

Let's consider the example provided in the question, where we want to add 1 to numbers greater than or equal to 45 and 5 to numbers less than 45 in a list:

l = [22, 13, 45, 50, 98, 69, 43, 44, 1]
result = [x+1 if x >= 45 else x+5 for x in l]

print(result)

Output:
[27, 18, 46, 51, 99, 70, 48, 49, 6]

In this example, the conditional expression x 1 if x >= 45 else x 5 specifies that the modified value should be x 1 if x is greater than or equal to 45; otherwise, it should be x 5.

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