Generator in if-statement in python

Question

Or How to if-statement in a modified list.

I've been reading StackOverflow for a while (thanks to everyone). I love it. I also seen that you can post a question and answer it yourself. Sorry if I duplicate, but I didn't found this particular answer on StackOverflow.

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• How do you verify if a element is in a list but modify it in the same time?

My problem:

myList = ["Foo", "Bar"]
if "foo" in myList:
  print "found!"

As I don't know the case of the element in the list I want to compare with lower case list. The obvious but ugly answer would be:

myList = ["Foo", "Bar"]
lowerList = []

for item in myList:
  lowerList.append(item.lower())

if "foo" in lowerList:
  print "found!"

Can I do it better ?

Answer 1

List comprehensions:

mylist = ["Foo", "Bar"]
lowerList = [item.lower() for item in mylist]

Then you can do something like if "foo" in lowerlist or bypass the temporary variable entirely with if "foo" in [item.lower() for item in mylist]

Answer 2

How about:

theList = ["Foo", "Bar"]
lowerCaseSet = set(x.lower for x in theList)

if "foo" in lowerCaseSet:
   print "found"

BTW. you shouldn't call your variable list as this word is already used by list type.

Answer 3

if any(s.lower() == "foo" for s in list): print "found"

Answer 4

I will respond to myself as it can help someone else:

We can use Generator directly in the If-statement to generate the modified list on the go.

list = ["Foo", "Bar"]
if "foo" in (item.lower() for item in list):
  print "found!"

The parentheses around the for-statement IS the generator. It will compute all the item on the fly and so, we will be able to compare our string to the modified one.

This is very useful and save memory (especially for big list) so you don't have to create a second list and you can keep your first list intact.

The downside is that is make the code harder to understand when you read it (especially when you are not use to generator).

Answer 5

This combines the memory advantages of a generator expression with the speed gains from removing duplicates:

if "foo" in (s.lower() for s in set(list)): print "found"

Answer 6

Please do not use list as variable name, here is version which puts generator to variable and demonstrates, that generation stopped after finding the answer and did not exhaust the generator:

list_to_search = ["Foo", "Bar"]
lowergen = (item.lower() for item in list_to_search)
if "foo" in lowergen:
  print "found!"
print next(lowergen), 'is next after it'