Python, print delimited list

Question

Consider this Python code for printing a list of comma separated values

for element in list:
    print element + ",",

What is the preferred method for printing such that a comma does not appear if element is the final element in the list.

ex

a = [1, 2, 3]
for element in a
  print str(element) +",",

output
1,2,3,
desired
1,2,3

Answer 1

That's what join is for.

','.join([str(elem) for elem in a])

Answer 2

print ','.join(a)

Answer 3

>>> ','.join(map(str,a))
'1,2,3'

Answer 4

A ','.join as suggested in other answers is the typical Python solution; the normal approach, which peculiarly I don't see in any of the answers so far, is

print ','.join(str(x) for x in a)

known as a generator expression or genexp.

If you prefer a loop (or need one for other purposes, if you're doing more than just printing on each item, for example), there are of course also excellent alternatives:

for i, x in enumerate(a):
  if i: print ',' + str(x),
  else: print str(x),

this is a first-time switch (works for any iterable a, whether a list or otherwise) so it places the comma before each item but the first. A last-time switch is slightly less elegant and it work only for iterables which have a len() (not for completely general ones):

for i, x in enumerate(a):
  if i == len(a) - 1: print str(x)
  else: print str(x) + ',',

this example also takes advantage of the last-time switch to terminate the line when it's printing the very last item.

The enumerate built-in function is very often useful, and well worth keeping in mind!

Answer 5

>>> a=[1,2,3]
>>> a=[str(i) for i in a ]
>>> s=a[0]
>>> for i in a[1:-1]: s="%s,%s"%(s,i)
...
>>> s=s+","+a[-1]
>>> s
'1,2,3'