python idiomatic python for loop if else statement

问题:

How can I use else statement in an idiomatic Python for loop? Without else I can write e.g.:

res = [i for i in [1,2,3,4,5] if i < 4]

The result is: [1, 2, 3]

The normal form of the above code is:

res = [] for i in [1,2,3,4,5]:     if i < 4:         res.append(i)

The result is the same as in idiomatic form: [1, 2, 3]

And I want this:

res = [i for i in [1,2,3,4,5] if i < 4 else 0]

I get SyntaxError: invalid syntax. The result should be: [1, 2, 3, 0, 0] The normal code of this is:

res = [] for i in [1,2,3,4,5]:     if i < 4:         res.append(i)     else:         res.append(0)

The result is: [1, 2, 3, 0, 0]

回答1:

You were close, you just have to move the ternary to the part of the list comprehension where you're creating the value.

res = [i if i < 4 else 0 for i in range(1,6)] 

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