How Can I Effectively Use if/else Logic within Python List Comprehensions?

Conditional Expressions in List Comprehensions for if/else

In Python, it's possible to translate for-loops containing if/else statements into list comprehensions using conditional expressions. Let's revisit a common scenario:

For-loop with if/else:

results = []
for x in xs:
    results.append(f(x) if x is not None else '')

Here, we aim to append the result of f(x) to results if x is not None; otherwise, we append an empty string.

Attempting to convert this to a list comprehension as follows:

[f(x) for x in xs if x is not None else '']

will result in a SyntaxError. The correct syntax is:

[f(x) if x is not None else '' for x in xs]

In general, the syntax for list comprehensions with if/else is:

[f(x) if condition else g(x) for x in sequence]

Where f(x) and g(x) represent the expressions to be evaluated based on the condition.

Conditional expressions, used in the above syntax, serve the same purpose as the ternary operator ?: found in other programming languages. For instance:

value = 123
print(value, 'is', 'even' if value % 2 == 0 else 'odd')

This concisely expresses that if value is divisible by 2, the output should be "even"; otherwise, it should be "odd."

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