python for循环中的赋值可能吗？

Question

I have a dictionary d (and a seperate sorted list of keys, keys ). I wanted the loop to only process entries where the value is False - so i tried the following:

for key in keys and not d[key]:
 #do foo

I suppose my understanding of python sytax is not what i thought it was - because the assignment doesnt suppose to have happened above, and ai get an instanciation error.

The below works of course, but I'd really like to be able to use something like the code above.. possible?

for key in keys:
 if d[key]: continue
  #foo time!

Thanks!

Answer 1

Use a genex for this.

for key in (k for k in keys if not d[k]):
   ....

Answer 2

If you dict was opposite (True iff the value should be scanned) you could use:

for key in filter(d.get, keys):
    ...

Answer 3

import itertools as it

for key in it.ifilterfalse(d.get, keys):
   ...

itertools often offers the best ways to pack functionality into iterations (==loops;-).