Iterate over non None items in Python

Question

I have a list of strings, some which happen to be None:

headers = ['Name', None, 'HW1', 'HW2', None, 'HW4', 'EX1', None, None]

Now I would like to iterate over this list, but skip the None entries. For instance, something like this would be nice:

for header in headers if header: print(header)

But this doesn't work. There are two ways I could get this to work, but I don't like either method:

for header in (item for item in headers if item): print(header)

and

for header in headers:
    if header: print(header)

I just was curious if there was a better way. I feel like ignoring None's should be quite fundamental.

Answer 1

headers = ['Name', None, 'HW1', 'HW2', None, 'HW4', 'EX1', None, None]
for header in filter(None, headers):
    print header

Answer 2

You can use filter:

headers = filter(None, headers)

Answer 3

You can get rid of the None items with a list comprehension:

headers = [item for item in headers if item is not None]
for item in header:
    print item

Answer 4

You can filter out the Nones with a simple list comprehension:

headers = [header for header in headers if header]

Then call your code:

for header in headers:
    print(header)