How would you make a comma-separated string from a list of strings?

What would be your preferred way to concatenate strings from a sequence such that between every two consecutive pairs a comma is added. That is, how do you map, for instance, ['a', 'b', 'c'] to 'a,b,c'? (The cases ['s'] and [] should be mapped to 's' and '', respectively.)

I usually end up using something like ''.join(map(lambda x: x+',',l))[:-1], but also feeling somewhat unsatisfied.

my_list = ['a', 'b', 'c', 'd']
my_string = ','.join(my_list)

'a,b,c,d'

This won't work if the list contains integers

And if the list contains non-string types (such as integers, floats, bools, None) then do:

my_string = ','.join(map(str, my_list)) 

Why the map/lambda magic? Doesn't this work?

>>> foo = ['a', 'b', 'c']
>>> print(','.join(foo))
a,b,c
>>> print(','.join([]))

>>> print(','.join(['a']))
a

In case if there are numbers in the list, you could use list comprehension:

>>> ','.join([str(x) for x in foo])

or a generator expression:

>>> ','.join(str(x) for x in foo)

",".join(l) will not work for all cases. I'd suggest using the csv module with StringIO

import StringIO
import csv

l = ['list','of','["""crazy"quotes"and\'',123,'other things']

line = StringIO.StringIO()
writer = csv.writer(line)
writer.writerow(l)
csvcontent = line.getvalue()
# 'list,of,"[""""""crazy""quotes""and\'",123,other things\r\n'

Here is a alternative solution in Python 3.0 which allows non-string list items:

>>> alist = ['a', 1, (2, 'b')]

• a standard way

  >>> ", ".join(map(str, alist))
  "a, 1, (2, 'b')"
  

• the alternative solution

  >>> import io
  >>> s = io.StringIO()
  >>> print(*alist, file=s, sep=', ', end='')
  >>> s.getvalue()
  "a, 1, (2, 'b')"
  

NOTE: The space after comma is intentional.