Mike H wrote:
Hello all, I have a question about the if/else aspect of list comprehension:
I would like to go through a list and place quotes around an item if
it is a string, and keep the item the same if it's anything else:
e.g.['a',9,'8b'] --> ['"a"', 9, '"8b"']
I understand that if/else list comprehension should be generally:
b=[(F,T)[boolean test] for val in X]
so, I tried the following code:
a=['test',1,'two']
b=[(inst, '"'+inst+'"')[isinstance(inst, str)] for inst in a]
I end up getting the error: unsupported operand type(s) for +: 'int' and 'str'
>From playing around with other examples, I get the feeling that Python
is calculating both values (inst and '"'+inst+'"') before selecting
which one to pass to the new list. Am I right? Is there any way I can
do this using list comprehension?
Thanks in advance,
Michael
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While I think your goal is of questionable value, this will do it:
b = [('"'+inst+'"' if isinstance(inst, str) else inst) for inst in a]
The parentheses around the conditional are unnecessary, but help with
readability I think.
Better yet:
def QuoteIfString(inst):
...
b = [QuoteIfString(inst) for inst in a]
would be much more readable, and you could document
*why* you are doing this in the def of QuoteIfString
Gary Herron
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