清单理解与作业

Question

I'm new to Python and I try to convert this:

for source in data['Source']:
    for index in range(len(source)):
        if source == sources[index]:
            percent[index] += 1
            pass

to this:

sources = [percent[index]+=1 for source in data['Source'] for index in range(len(source)) if source == sources[index]]

but I give an error E0001 , after reading Python documentation I don't know how to convert this to a list comprehension.

Answer 1

Assignments are statements, which are not allowed in list comprehensions, which support only expressions.

You can use sum instead:

sources = {index: sum(1 for index in range(len(source)) if source == sources[index]) for source in data['Source']}

A more efficient method would be to use collections.Counter , as @Amadan has suggested in the comments:

import collections.Counter:
sources = Counter(index for source in data['Source'] for index in range(len(source)) if source == sources[index])