Automate the boring stuff with Python: Comma Code -

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currently working way through beginners book , have completed 1 of practice projects 'comma code' asks user construct program which:

takes list value argument , returns string items separated comma , space, , inserted before last item. example, passing below spam list function return 'apples, bananas, tofu, , cats'. function should able work list value passed it.

spam = ['apples', 'bananas', 'tofu', 'cats']

my solution problem (which works fine):

spam= ['apples', 'bananas', 'tofu', 'cats'] def list_thing(list):     new_string = ''     in list:         new_string = new_string + str(i)         if list.index(i) == (len(list)-2):             new_string = new_string + ', , '         elif list.index(i) == (len(list)-1):             new_string = new_string         else:             new_string = new_string + ', '     return new_string  print (list_thing(spam))

my question, there way can shorten code? or make more 'pythonic'?

use str.join() join sequence of strings delimiter. if words except last, can insert ' , ' there instead:

def list_thing(words):     if len(words) == 1:         return words[0]     return '{}, , {}'.format(', '.join(words[:-1]), words[-1])

breaking down:

  • words[-1] takes last element of list. words[:-1] slices list produce new list words except last one.

  • ', '.join() produces new string, strings of argument str.join() joined ', '. if there one element in input list, 1 element returned, unjoined.

  • '{}, , {}'.format() inserts comma-joined words , last word template (complete oxford comma).

if pass in empty list, above function raise indexerror exception; test case in function if feel empty list valid use-case function.

so above joins all words except last ', ', adds last word result ' , '.

note if there 1 word, 1 word; there nothing join in case. if there two, 'word1 , word 2'. more words produces 'word1, word2, ... , lastword'.

demo:

>>> def list_thing(words): ...     if len(words) == 1: ...         return words[0] ...     return '{}, , {}'.format(', '.join(words[:-1]), words[-1]) ... >>> spam = ['apples', 'bananas', 'tofu', 'cats'] >>> list_thing(spam[:1]) 'apples' >>> list_thing(spam[:2]) 'apples, , bananas' >>> list_thing(spam[:3]) 'apples, bananas, , tofu' >>> list_thing(spam) 'apples, bananas, tofu, , cats'

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