在 Python 中查找逗号分隔列表中的第 N 个项目

Question

I have a large CSV with comma separated lines of varying length. Sorting another set of data I used split(',') in a loop to separate fields, but this method requires each line to have the same number of entries. Is there a way I can look at a line and, independent of the total number of entries, just pull the Nth item? For reference, the method I was using will only work with a line that looks like AAA,BBB,CCC,DDD

entry = 'A,B,C,D'

(a,b,c,d) = entry.split(',')
print a,b,c,d

But I would like to pull A and C even if it looks like A,B,C,D,E,F or A,B,C.

Answer 1

Use a list instead of separate variables.

values = entry.split(',')
print values[0], values[2]

Answer 2

Just use a list:

xyzzy = entry.split(",");
print xyzzy[0], xyzzy[2]

But be aware that, once you allow the possibility of variable element counts, you'd probably better allow for too few:

entry = 'A,B'
xyzzy = entry.split(",");
(a,c) = ('?','?')
if len(xyzzy) > 0: a = xyzzy[0]
if len(xyzzy) > 2: c = xyzzy[2]

print a, c

Answer 3

If you don't want to index the results, it's not difficult to write your own function to deal with the situation where there are either too few or two many values. Although it requires a few more lines of code to set up, an advantage is that you can give the results meaningful names instead of anonymous ones like results[0] and results[2] .

def splitter(s, take, sep=',', default=None):
    r = s.split(sep)
    if len(r) < take:
       r.extend((default for _ in xrange(take - len(r))))
    return r[:take]

entry = 'A,B,C'
a,b,c,d = splitter(entry, 4)
print a,b,c,d  # --> A B C None

entry = 'A,B,C,D,E,F'
a,b,c,d = splitter(entry, 4)
print a,b,c,d  # --> A B C D