Automate the boring stuff with Python: Comma Code


Currently working my way through this beginners book and have completed one of the practice projects ‘Comma Code’ which asks the user to construct a program which:

takes a list value as an argument and returns
a string with all the items separated by a comma and a space, with and
inserted before the last item. For example, passing the below spam list to
the function would return ‘apples, bananas, tofu, and cats’. But your function
should be able to work with any list value passed to it.

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

My solution to the problem (Which works perfectly fine):

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

print (list_thing(spam))

My only question, is there any way I can shorten my code? or make it more ‘pythonic’?

Here is my code.

def listTostring(someList):
    a = ''
    for i in range(len(someList)-1):
        a += str(someList[i])
    a += str('and ' + someList[len(someList)-1])
    print (a)

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

output: apples, bananas, tofu, and cats


Use str.join() to join a sequence of strings with a delimiter. If you do so for all words except for the last, you can insert ' and ' there instead:

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

Breaking this down:

  • words[-1] takes the last element of a list. words[:-1] slices the list to produce a new list with all words except the last one.

  • ', '.join() produces a new string, with all strings of the argument to str.join() joined with ', '. If there is just one element in the input list, that one element is returned, unjoined.

  • '{}, and {}'.format() inserts the comma-joined words and the last word into a template (complete with Oxford comma).

If you pass in an empty list, the above function will raise an IndexError exception; you could specifically test for that case in the function if you feel an empty list is a valid use-case for the function.

So the above joins all words except the last with ', ', then adds the last word to the result with ' and '.

Note that if there is just one word, you get that one word; there is nothing to join in that case. If there are two, you get 'word1 and word 2'. More words produces 'word1, word2, ... and lastword'.


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

Others have given great one-liner solutions, but a good way to improve your actual implementation – and fix the fact that it does not work when elements are repeated – is to use enumerate in the for loop to keep track of the index, rather than using index which always finds the first occurrence of the target.

for counter, element in enumerate(list):
    new_string = new_string + str(element)
    if counter == (len(list)-2):
Answered By: Daniel Roseman

I tried this, hope this is what you are looking for :-

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

def list_thing(list):

#creating a string then splitting it as list with two items, second being last word
    new_string=', '.join(list).rsplit(',', 1)    

#Using the same method used above to recreate string by replacing the separator.

    new_string=' and'.join(new_string)
    return new_string

Answered By: Utkarsh

Here’s a solution that handles the Oxford comma properly. It also copes with an empty list, in which case it returns an empty string.

def list_thing(seq):
    return (' and '.join(seq) if len(seq) <= 2
        else '{}, and {}'.format(', '.join(seq[:-1]), seq[-1]))

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

for i in range(1 + len(spam)):
    seq = spam[:i]
    s = list_thing(seq)
    print(i, seq, repr(s))


0 [] ''
1 ['apples'] 'apples'
2 ['apples', 'bananas'] 'apples and bananas'
3 ['apples', 'bananas', 'tofu'] 'apples, bananas, and tofu'
4 ['apples', 'bananas', 'tofu', 'cats'] 'apples, bananas, tofu, and cats'

FWIW, here’s a slightly more readable version using an if-else statement instead of a conditional expression:

def list_thing(seq):
    if len(seq) <= 2:
        return ' and '.join(seq)
        return '{}, and {}'.format(', '.join(seq[:-1]), seq[-1])    

And here’s a slightly less readable version, using an f-string:

def list_thing(seq):
    if len(seq) <= 2:
        return ' and '.join(seq)
        return f"{', '.join(seq[:-1])}, and {seq[-1]}"   

Note that Martijn’s code produces 'apples, and bananas' from the 2 item list. My answer is more grammatically correct (in English), however Martijn’s is more technically correct because it does exactly what’s specified in the OP’s quote (although I disagree with his handling of the empty list).

Answered By: PM 2Ring

I used a different approach. I am a beginner, so I don’t know if it’s the cleanest way to do it. To me it seemed as the most simple way:

spam = ['apples', 'pizza', 'dogs', 'cats']

def comma(items):
    for i in range(len(items) -2):
        print(items[i], end=", ")# minor adjustment from one beginner to another: to make it cleaner, simply move the ', ' to equal 'end'. the print statement should finish like this --> end=', '
    print(items[-2] + 'and ' + items[-1]) 


Which will give the output:

apples, pizza, dogs and cats
Answered By: Hein de Wilde

That one wins for simplicity Hein.

Only, the author specified:

"your function should be able to work with any list value passed to it."

To accompany non strings, add str() tags to al the [i] functions.

spam = ['apples', 'bananas', 'tofu', 'cats', 'bears', 21]
def pList(x):
    for i in range(len(x) - 2):
        print(str(x[i]) + ', ', end='')
    print(str(x[-2]) + ' and ' + str(x[-1]))
Answered By: Bojangles

This is what I did, IMO it is more intuitive…

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

def ipso(x):
    print("'" , end="")
    def run (x):

    for i in range(len(x)):
        print(x[i]+ "" , end=',')


Answered By: armature hour
spam=['apple', 'banana', 'tofu','cats']
spam[-1]= 'and'+' '+ spam[-1]
print (', '.join((spam)))
Answered By: Amunir

Why is everyone putting so complex codes.

See my code below. Its the most simple and easiest to understand at one go even for a beginner.

import random

def comma_code(subject):

     a = (len(list(subject)) - 1)

     for i in range(0, len(list(subject))):

          if i != a:
               print(str(subject[i]) + ', ', end="")

              print('and '+ str(subject[i]))            

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

after coding the above, just type comma_code(spam) in the python shell and you are good to go. Enjoy

Answered By: Sannidhya
def commacode(mylist):
    mylist[-1] = 'and ' + mylist[-1]
    mystring = ', '.join(mylist)
    return mystring

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

print commacode(spam)
Answered By: bojaraja

The format statement is cleaner.

This worked for me as well:

def sentence(x):
    if len(x) == 1:
        return x[0]
    return (', '.join(x[:-1])+ ' and ' + x[-1])
Answered By: nnaji
def val(some_parameter):

for i in range(0,len(spam)):
if i!=(len(spam)-1):
print(spam[i]+', ',end="")
print('and '+spam[-1]+"'")
Answered By: aditi telang

My interpretation of the question is such that a single list item would also be the last list item, and as such would need the ‘and’ inserted before it, as well as a two item list returning both with ‘, and‘ between them. Hence no need to deal with single or two item lists seperately, just the first n items, and the last item.
I’d also note that while great, a lot of the other items use modules and functions not taught in the Automate the Boring Stuff text by the time the student encounters this question (a student like me had seen join and .format elsewhere, but attempted to only use what had been taught in the text).

def commacode(passedlist):
    stringy = ''
    for i in range(len(passedlist)-1):
        stringy += str(passedlist[i]) + ', '
        # adds all except last item to str
    stringy += 'and ' + str(passedlist[len(passedlist)-1])
    # adds last item to string, after 'and'
    return stringy

And you could handle the empty list case by:

def commacode(passedlist):
    stringy = ''
        for i in range(len(passedlist)-1):
            stringy += str(passedlist[i]) + ', '
            # adds all except last item to str
        stringy += 'and ' + str(passedlist[len(passedlist)-1])
        # adds last item to string, after 'and'
        return stringy
    except IndexError:
        return '' 
        #handles the list out of range error for an empty list by returning ''
Answered By: toonarmycaptain

I am a fairly new pythonista. In the question it was asked that the function return the list contents as a string in the format that the other solutions in this forum have ‘printed’ it. Following is (in my opinion) a cleaner solution to this problem.

This illustrates the comma code solution of chapter 4 [Lists] in Automate The Boring Stuff.

def comma_code(argument):

    argument_in_string = ''
    argument_len = len(argument)
    for i in range(argument_len):
        if i == (argument_len - 1):
            argument_in_string = argument_in_string + 'and ' + argument[i]
            return argument_in_string

        argument_in_string = argument_in_string + argument[i] + ', '

spam = ['apples', 'bananas', 'tofu', 'cats']
return_value = comma_code(spam)
Answered By: Ashutosh Kar

As the function must work for all list values passed to it, including integers, therefore it should be able to return/print all values i.e. as str(). My fully working code looks like this:

spam = ['apples', 'bananas', 'tofu', 'cats', 2]

def commacode(words):

    x = len(words)

    if x == 1:
        for i in range(x - 1):
            print((str(words[i]) + ','), end=' ')
        print(('and ' + str(words[-1])))

Answered By: Adam

Here’s my solution. Once I found the join method and how it worked, the rest followed.

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

def commas(h):
    s = ', '
    print(s.join(spam[0:len(spam)-1]) + s + 'and ' + spam[len(spam)-1])

Answered By: Philip Horky

Just a simple code. I think we don’t need to use any fancy stuff here. :p

def getList(list):
    value = ''
    for i in range(len(list)):
        if i == len(list) - 1:
            value += 'and '+list[i]
            value += list[i] + ', '
    return value

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

print('### TEST ###')
Answered By: HenriqueAdriano

I came up with this solution

#This is the list which needs to be converted to String
spam = ['apples', 'bananas', 'tofu', 'cats']

#This is the empty string in which we will append
s = ""

def list_to_string():
    global spam,s
    for x in range(len(spam)):
        if s == "":
            s += str(spam[x])
        elif x == (len(spam)-1):
            s += " and " + str(spam[x])
            s += ", " + str(spam[x])
    return s

a = list_to_string()
Answered By: KshitijV97

As it was not mentioned, here’s an answer with f string, for reference:

def list_things(my_list):
    print(f'{", ".join(my_list[:-1])} and {my_list[-1]}.')

An example interpolating a custom message and accepting also a string as argument:

def like(my_animals = None):
    message = 'The animals I like the most are'
    if my_animals == None or my_animals == '' or len(my_animals) == 0:
        return 'I don't like any animals.'
    elif len(my_animals) <= 1 or type(my_animals) == str:
        return f'{message} {my_animals if type(my_animals) == str else my_animals[0]}.'
    return f'{message} {", ".join(my_animals[:-1])} and {my_animals[-1]}.'

>>> like()
>>> like('')
>>> like([])
# 'I don't like any animals.'

>>> like('unicorns') 
>>> like(['unicorns']) 
# 'The animals I like the most are unicorns.'

>>> animals = ['unicorns', 'dogs', 'rabbits', 'dragons']
>>> like(animals) 
# 'The animals I like the most are unicorns, dogs, rabbits and dragons.'
Answered By: Анна

I was not satisfied with any of the solutions because none handle the case with or, e.g. apples, bananas, or berries

def oxford_comma(words, conjunction='and'):
    conjunction = ' ' + conjunction + ' '

    if len(words) <= 2:
        return conjunction.join(words)
        return '%s,%s%s' % (', '.join(words[:-1]), conjunction, words[-1])

Otherwise, this solution is more-or-less identical to the one provided by @PM2Ring

Answered By: user2426679

No loops, no joins, just two print statements:

def commalist(listname):
    print(*listname[:-1], sep = ', ',end=", "),
Answered By: Mike K

This code works no matter what data types are in the lists, boolean, int, string, float, etc.

def commaCode(spam):
    count = 0
    max_count = len(spam) - 1

    for x in range(len(spam)):
        if count < max_count:
            print(str(spam[count]) + ', ', end='')
            count += 1
            print('and ' + str(spam[max_count]))

spam1 = ['cat', 'bananas', 'tofu', 'cats']
spam2 = [23, '', True, 'cats']
spam3 = []

Answered By: Randomizer

I am working through the same book and came up with this solution:
This allows the user to input some values and create a list from the input.

userinput = input('Enter list items separated by a space.n')
userlist = userinput.split()

def mylist(somelist):
    for i in range(len(somelist)-2): # Loop through the list up until the second from last element and add a comma
        print(somelist[i] + ', ', end='')
    print(somelist[-2] + ' and ' + somelist[-1]) # Add the last two elements of the list with 'and' in-between them



user input: one two three four five
Output: one, two, three, four and five

Answered By: Mark Archer

This is what I came up with. There’s probably a much cleaner way to write this, but this should work with any sized list as long as there’s at least one element in the list.

spam = ['apples', 'oranges' 'tofu', 'cats']
def CommaCode(list):
    if len(list) > 1 and len(list) != 0:
        for item in range(len(list) - 1):
            print(list[item], end=", ")
        print('and ' + list[-1])
    elif len(list) == 1:
        for item in list:
        print('List must contain more than one element')
Answered By: SamRR_75
def sample(values):
    if len(values) == 0:
         print("Enter some value")
    elif len(values) == 1:
        return values[0]
        return ', '.join(values[:-1] + ['and ' + values[-1]])

spam = ['apples', 'bananas', 'tofu', 'cats']
Answered By: Raghav
def listall(lst):               # everything "returned" is class string
    if not lst:                 # equates to if not True. Empty container is always False
        return 'NONE'           # empty list returns string - NONE
    elif len(lst) < 2:          # single value lists
        return str(lst[0])      # return passed value as a string (do it as the element so 
                                #  as not to return [])
    return (', '.join(str(i) for i in lst[:-1])) + ' and ' + str(lst[-1])
        # joins all elements in list sent, up to last element, with (comma, space) 
        # AND coverts all elements to string. 
        # Then inserts "and". lastly adds final element of list as a string.

This isn’t designed to answer the original question. It’s to show how to define the function addressing all the matters requested by the book without being complex. I think that’s acceptable as the original question posts the books "Comma Code" test. Important Note: Something I found confusing that might help others is. "a list value" means a value of type list or "an entire list" it doesn’t mean an individual value (or slices) from "type list". Hope that’s helpful

Here are the samples I used to test it:

empty = []
ugh = listall(empty)
test = ['rabbits', 'dogs', 3, 'squirrels', 'numbers', 3]
ughtest = listall(test)
supertest = [['ra', 'zues', 'ares'],
            ['Who said', 'biscuits', 3, 'or', 16.71]]
one = listall(supertest[0])
two = listall(supertest[1])
last = listall(supertest[2])

Answered By: Armagon
listA = [ 'apples', 'bananas', 'tofu' ]
def commaCode(listA):
    s = ''
    for items in listA:
        if items == listA [0]:
            s = listA[0]
        elif items == listA[-1]:
            s += ', and ' + items
            s += ', ' + items
    return s
Answered By: new_to_code

I didn’t dig through all the answers but I did see someone suggested using join. I agree but since this question didn’t come in the book before learning joins my answer was this.

def To_String(my_list)
        for index, item in enumerate(my_list):
            if index == 0:                       # at first index
                myStr = str(item) + ', '
            elif index < len(my_list) - 1:       # after first index
                myStr += str(item) + ', '
                myStr += 'and ' + str(item)      # at last index
        return myStr  

    except NameError:
        return 'Your list has no data!'

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

my_string = To_String(spam)



apples, bananas, tofu, and cats
Answered By: Dan

First, I’m only two months in doing python and coding in general.

This took 2hr+ to solve because I had put my empty list variable as lst = [], instead of using lst = "" ……Not sure why yet.

        user_input = input().split()
        lst = "" # I had this as lst = [] but doesn't work I don't know why.... yet
        for chars in user_input:
            if chars == user_input[0]:
                lst += user_input[0]
            elif chars  == user_input[-1]:
                lst += ", and " + chars
                lst += ", " + chars


Edit: More details

The .split() function will put our user input(string value) into a list. That gives us indexes now and we can use our for loop. The lst empty string variable still a work in progress understanding. Next, in our for loop look at each index and if that index matches our boolean value we add what we want to our list. In this case either nothing or a , and or lastly just another , (comma) . Then print.

That said majority of the answers have the .join method in it, but at this part of the book this isn’t talked about. That’s chapter 6

Basically that is like me teaching you addition and subtraction then give you a test on fractions. We are not fraction ready yet, and just cased confusion, at least for me. Not to mention no one even gave the documentation on it. .join() method a few areas to view documentations and examples are located here if anyone needs:


Answered By: JQTs
edgecase = []
edgecase2 = ['apples','bananas']
supplies = ['pens','staples','flamethrowers','binders']

def list2string(list):
    string = ''
    for index, value in enumerate(list):
        if len(list) == 1:
            string = value
        elif index == len(list)-2:
            string += value + ' '
        elif index < len(list)-2:
            string += value + ',' + ' '
            string += 'and ' + value
    return string



: pens, staples, flamethrowers and binders
: apples and bananas
Answered By: John Henry Erikson
mijn_lijst = ['tafel', 'stoel', 'bank', 'tv-meubel']

def comma_code(verander):
    nieuwe_lijst = ''
    for i in verander[0:-1]:
        x = nieuwe_lijst = nieuwe_lijst + f'{i}, '
    x = x + f' and {mijn_lijst[-1]}'
    return x

Answered By: Dakkie15

Here is how I implemented it, after learning a bit about .join

def commaCode(list):
    strList = (', '.join(list[:-1]))
    lastItem = (''.join(list[-1]))
    print(f"{strList}, and {lastItem}")

pets = ['perrot', 'fish', 'dog', 'cat', 'hamster']


perrot, fish, dog, cat, and hamster
perrot, fish, and dog
Answered By: Anton Teren
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