Use list comprehension without iteration variable

Question

I wonder if there is a way to use e.g. a list comprehension without an iteration variable if I do not need it? For example, in this sample of code:

a = [random.randrange(-10, 11) / 10 for i in range(100)]

I get a warning "Local variable 'i' value is not used". Is there any variant of the list comprehension construct without iteration variable?

What IDE/editor are you using? You might be able to change `i` to `_` which is the common notation for "I deliberately mean to not be using this" and your IDE might ignore it, but otherwise - it's fine. — Jon Clements, May 29 '15 at 11:31

James Mills · Accepted Answer · 2015-05-29T11:35:29.107

4

Just discard the value of i:

a = [random.randrange(-10, 11) / 10 for _ in range(100)]

_ is considered the "last value" in Python and by convention is used as a "throw away" value.

edited May 29 '15 at 11:35

answered May 29 '15 at 11:32

James Mills

warning disappeared, but does that mean we are now using unnecessary variable _ instead of i? – zegoline May 29 '15 at 11:35
``_`` is considered the "last value" in Python and by convention is used as a "throw away" value. – James Mills May 29 '15 at 11:35
3

@zegoline Just need to be careful if you're using Python 2.x and have `ugettext` or which is commonly aliased as `_` (another convention) as a list-comp in Py 2.x will leak `_` to the outer scope. – Jon Clements May 29 '15 at 11:37
ok, I've got it, thanks a lot – zegoline May 29 '15 at 11:41
1

`_` is only the last value in the interactive interpreter. In a script it has no special meaning. – chepner May 29 '15 at 11:54
If you read what I said *carefully* that's precisely what I mean :) – James Mills May 29 '15 at 12:05

1 Answers1