Python 3 Filter - Bug Or Feature?

Okay, I am a complete newbie to Python - and stackoverflow. I am coming from a ksh and Perl background. The following in an interactive session with Python 2.7: Python 2.7.3

Solution 1:

As per the documentation, filter in Python 3.x returns an iterator, rather than a list as in version 2.x. This is more memory-efficient than generating the whole list up-front. If you want the list back, you can wrap the iterator in a list() call:

VALIDVALUES = list(filter(...))

Alternatively, and as recommended by What’s New In Python 3.0, you could rewrite it as a list comprehension without a lambda:

VALIDVALUES = [x for x in [...] if re.search(r'^' + KEY + '\=', x)]

Solution 2:

Note that you don't usually need a list of values. You can directly loop the output like below

for value in VALIDVALUES:
  do_some_thing(value)

or

for value in filter(...):
  do_some_thing(value)

Sometimes you may need unique values or non mutable values. Use set or tuple or frozenset instead of list as shown in the other answer.