How to emulate the increment (++) operator?

Question

My input is a list, say l

It can either contain 4 or 5 elements. I want to assign it to 5 variables , say a, b, c, d and e.

If the list has only 4 elements then the third variable (c) should be None.

If python had an increment (++) operator I could do something like this.

l = [4 or 5 string inputs]
i = -1
a = l[i++]
b = l[i++]
c = None
if len(l) > 4:
    c = l[i++]
d = l[i++]
e = l[i++]

I can't seem to find an elegant way to do this apart from writing i+=1 before each assignment. Is there a simpler pythonic way to do this?

You could do `a, b, c, d, e = l` or `a, b, d, e = l`, depending on the length. Maybe there's even more pythonic solution — Sergio Tulentsev, Jan 11 '20 at 18:54
Aside from unpacking, is there anything wrong with referring to them in the list? — AMC, Jan 12 '20 at 04:35
Sorry, I meant to ask if you can just use `my_list[0]`, `my_list[1]` etc. instead of assigning them to variables. — AMC, Jan 12 '20 at 17:36

score 10 · Accepted Answer · answered Jan 11 '20 at 18:55

You're trying to use a C solution because you're unfamiliar with Python's tools. Using unpacking is much cleaner than trying to emulate ++:

a, b, *c, d, e = l
c = c[0] if c else None

The *c target receives a list of all elements of l that weren't unpacked into the other targets. If this list is nonempty, then c is considered true when coerced to boolean, so c[0] if c else None takes c[0] if there is a c[0] and None otherwise.

SethMMorton · Answer 2 · 2021-11-27T15:46:20.860

In the specific case of this question, list unpacking is the best solution.

For other users needing to emulate ++ for other purposes (typically the desire to increment without an explicit i += 1 statement), they can use itertools.count. This will return an iterator that will increment indefinitely each time it is passed to next().

import itertools

i = itertools.count(0)  # start counting at 0
print(next(i))  # 0
print(next(i))  # 1
# ...and so on...

Simon Notley · Answer 3 · 2020-01-11T18:55:56.863

0

I can't see that you really need to be incrementing at all since you have fixed positions for each variable subject to your c condition.

l = [4 or 5 string inputs]

a = l[0]
b = l[1]

if len(l) > 4:
    c = l[2]
    d = l[3]
    e = l[4]
else:
    c = None
    d = l[2]
    e = l[3]

edited Jan 11 '20 at 18:55

answered Jan 11 '20 at 18:53

Simon Notley

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I want to avoid doing stuff like what you have done up there. – dCoder Jan 11 '20 at 18:55
Stuff like what? And why? – Simon Notley Jan 11 '20 at 18:56

MasterOfTheHouse · Answer 4 · 2020-01-11T19:32:25.503

0

There is no ++ operator in Python. A similar question to this was answered here Behaviour of increment and decrement operators in Python

edited Jan 11 '20 at 19:32

answered Jan 11 '20 at 19:15

MasterOfTheHouse

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How to emulate the increment (++) operator?

4 Answers4