Question

If you have a long running list comprehension in Python, say:

from itertools import combinations

print [w for w in (''.join(c) for c in combinations(words, 2)) if sorted(w) == letters]

where words is a list of 200000 words and letters is a list of letters; is there any way to occasionally print out how many words has been processed so far or some other form of progress report?

Answer 1

You’ll need to convert it to a normal loop; don’t try to mix in a side-effect function:

from itertools import combinations

result = []
count = 0
for w in (''.join(c) for c in combinations(words, 2)):
    if sorted(w) == letters:
        result.append(w)
        count += 1
        if count % 2000 == 0:
            print 'Progress: {0} matching combinations found'.format(count)

print result

or, if you want to track combinations tested, move the count before the if:

from itertools import combinations

result = []
count = 0
for w in (''.join(c) for c in combinations(words, 2)):
    count += 1
    if count % 2000 == 0:
        print 'Progress: {0} combinations scanned'.format(count)

    if sorted(w) == letters:
        result.append(w)

print result