Python: add new line every n strings in a list

Question

I have a list of pairs to convert to strings (for later printing) and I want to insert a \n every three pairs. I could do as in my following sample code, but is there a more compact way in Python?

pairs = [[1,2] for i in range(10)] #my data
pairs = [str(p) + ', ' for p in pairs]
for i in reversed(range(0, len(pairs), 3)):
    if i == 0:
        continue
    pairs.insert(i, '\n')
pairs = ''.join(pairs)
pairs = pairs [:-2] #removing the last ', '

This way, I get:

>>> print pairs
[1, 2], [1, 2], [1, 2], 
[1, 2], [1, 2], [1, 2], 
[1, 2], [1, 2], [1, 2], 
[1, 2]

RemcoGerlich · Accepted Answer · 2013-12-18 10:02:48Z

3

Possibly use a helper generator that yields the values from pairs, and a '\n' after every three:

def add_after_every_n(iterator, item_to_add='\n', after_every=3):
    for i, element in enumerate(iterator, 1):  # i counts from 1
         yield element
         if i % after_every == 0:
            yield item_to_add

pairs = [[1,2] for i in range(10)]
pairs = [str(p) + ', ' for p in pairs]
pairs_string = ''.join(add_after_every_n(pairs))
pairs_string = pairs_string[:-2]  # remove last ', '

answered Dec 18, 2013 at 10:02

RemcoGerlich

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