CODEWITHSUNDEEP
python
Steve
Steve

Reputation: 8293

if else for None in Python

Any way to write this in one line in Python, or even better, as an expression instead of a statement?

parts = ['0', '1', 'None', '5', '4']
[int(p) for p in parts]

This of course gives an error,

ValueError: invalid literal for int() with base 10: 'None'

So:

[p=='None' and None or int(p) for p in parts]

Doesn't work because you can't use None with the and/or construct reliably. (Even if p=='None' is true, None is equivalent to false so it goes to the or part.)

[int(p) if p=='None' else None for p in parts]

Also doesn't work. I guess it evaluates int(p) before the conditions? (Seems odd semantics.)

a = []
for p in parts:
    if p=='None': k = None; else: k = int(p)
    a.append(k)

Nope, invalid syntax.

a = []
for p in parts:
    if p=='None':
        k = None;
    else:
        k = int(p)
    a.append(k)

Ah! Finally. But isn't there a shorter way to write such a simple loop?

Upvotes: 0

Views: 22856

Answers (5)

thiruvenkadam
thiruvenkadam

Reputation: 4260

A simpler solution will be:

parts = ['0', '1', 'None', '5', '4']
[int(p) for p in parts if p.isdigit()]

However, float is not accepted here. If float string(?? I dont know what to call that) to integer is a necessity, you can consider the following:

parts = ['0', '1', 'None', '5', '4']
[int(p.split(".")[0]) for p in parts if p.replace(".", "", 1).isdigit()]

Upvotes: 0

xorsyst
xorsyst

Reputation: 8257

Do you really only have 1 place in your code where you need this transform? If not, define a function and then make it multiple lines, commented, and easy to follow. That way you hide the complexity of your code, and keep the main code simple to read.

Upvotes: 0

Hyperboreus
Hyperboreus

Reputation: 822

[ [int, eval] [p=='None'] (p) for p in parts]

Should be save as eval is only called on string 'None'.

Upvotes: 4

bluepnume
bluepnume

Reputation: 17138

Almost had it:

[int(p) if p != 'None' else None for p in parts]

Upvotes: 7

Sven Marnach
Sven Marnach

Reputation: 602685

You almost got it right:

[None if p == 'None' else int(p) for p in parts]

Upvotes: 14

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