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I'm working on a project from Chapter 4 of Automate the Boring Stuff with Python. Here's the project's prompt:

"For practice, write programs to do the following tasks. Comma Code Say you have a list value like this: spam = [' apples', 'bananas', 'tofu', 'cats'] Write a function that 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 previous 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."

I wrote a script that creates a list with commas and an 'and' before the last item: But I can't figure out how to make the script work with any list value passed to it. I've tried using the input function to call a list, but that doesn't work (or I can't get to work), since the input function only receives strings and not list names?

Here's the farthest I've gotten:

def listToString(list):
    if list[-1]:
        list.append('and '+str(list[-1]))
        list.remove(list[-2])
    for i in range(len(list)):
        print(''+list[i]+', ')

spam = ['apples', 'bananas', 'tofu', 'cats']
listToString(spam)

As far as using the input() function, here's the code I've tried to no avail. I enter the spam list in the shell editor and run this:

def listToString(list):
    if list[-1]:
        list.append('and '+str(list[-1]))
        list.remove(list[-2])
    for i in range(len(list)):
        print(''+list[i]+', ')

list = input("What list do you want to use?")
listToString(list)
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1
  • 1
    This function is underspecified. An empty list doesn't have a last element, ['apples'] probably shouldn't become 'and apples', and ['apples', 'bananas'] probably shouldn't have a comma in the output. Commented Nov 17, 2015 at 23:34

12 Answers 12

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4

Here's a simple solution which only uses syntax already covered by Chapter 4:

def toString(arr):
    s = ''
    for i in range(len(arr)):
        if i > 0:
            if i == len(arr) - 1:
                # last one
                s = s + ' and '
            else:
                # second, third, ...
                s = s + ', '
        s = s + arr[i];
    return s

It works for arrays with any number of elements.

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Comments

3

I think that the easiest way is to substitute the last element with "and ...." and then join everything with ", "

def merge(list):
  return ', '.join(list[:-1] + ['and '+list[-1]])
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2

This solution is solely based on basic principles covered up to chapter 4. It makes liberal use of the "end" parameter presented in Chapter 3. 

spam = ['apples', 'bananas', 'tofu', 'cats']
print("'", end='')
for i in range(len(spam)-1):
    print(spam[i], end=', ')
print('and '+str(spam[-1]), end='')
print("'")
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1

I believe "But your function should be able to work with any list value passed to it." means that you shouldn't hard code the example list (['apples', 'bananas', 'tofu', 'cats']) in the function.

So, the simplest form of the function would be:

def listToString(list):
    return "{} and {}".format(", ".join(list[:-1]]), list[-1])

but when you want to process other types than strings and fewer than 2 elements, the function becomes:

def listToString(list):
    length = len(list)
    if length == 0 :
        return ""
    elif length == 1 :
        return "{}".format(list[0])
    else:
        strings = ["{}".format(x) for x in list[:-1]]
        return "{} and {}".format(", ".join(strings), list[-1])
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1

Here's my solution:

spam = ['zero', 'one', 'two', 'three', 'second to last', 'last']

def func(listValue):
    print('\'', end='')    # Openning single quote.
    for i in range(len(listValue[:-2])):    # Iterate through all values in the list up to second to last.
        print(str(listValue[i]), end=', ')
        continue
    print(str(listValue[-2]) + ' and ' + str(listValue[-1]) + '\'')    # Add second to last and last to string separated by 'and'. End with a single quote.

listValue = spam
func(listValue)

    # Will do for any list.

Output is:

'zero, one, two, three, second to last and last'

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0

Below is my solution for this problem. Along with my comments for each line of code. Hope this helps. 

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

# function should return 'apples, bananas, tofu, and cats' 

def listToString(list):

    newString = '' # create an empty string variable 

    # for loop that iterates through length of list 
    for index in range(len(list)):
        # put a comma and space after each word except the last one 
        if index in range(len(list)-1): 
            newString += list[index] + ',' + ' '
        else:
            newString += 'and' + ' ' #put the word and + a space
            #finally put the last word from the list 
            #spam in the string newString
            newString += list[index] 

       #return newString value
       return '{}'.format(newString) 

listToString(spam)

Output:

'apples, bananas, tofu, and cats'
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0

Here's the solution I came up with after one week of learning python:

spam = ['apples', 'bananas', 'tofu', 'cats', 'rats', 'turkeys']
group = []
for i in range(len(spam)-1):
    group.append(spam[i])
print (', '.join(group),'& ' +spam[-1])

I was just working on this problem today during my new python hobby.

I know my solution isn't quite as compact and elegant as the top one. I basically just used a for statement to create a second list w/o the last entry, then used print to join that group add the "&" symbol and finally the last item.

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1 Comment

instead of a for loop, it'd be simpler to do print (', '.join(spam[:-1]), '& ' + spam[-1]), which is essentially the top answer. spam[:-1] is the list without the last entry. See slicing, which works the same for strings as for lists. Do ctrl+F and type "Slice".
0

This is what I came up with.

spam = ['apples', 'bananas', 'tofu', 'cats']
spam.insert(-1, ' and')
print(spam[0] + ', ' + spam[1] + ', ' + spam[2] + ',' + spam[3] + ' ' + spam[4])
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0

It's my solution

def converter(mylist):
    mystr=''
    if len(mylist)>1:
        for i in range(len(mylist)-1):
            mystr=mystr+str(mylist[i])+', '
        mystr=mystr+'and '+str(mylist[-1])
        print(mystr)
    elif len(mylist)==1:    
        mystr=mystr+str(mylist[0])
        print(mystr)
    else:
        print('Your list is empty')
spam = []
t='1'
while t != '':
    print('Input new value in list (Or enter nothing to stop)')
    t=str(input())
    if t != '':
        spam.append(t)
converter(spam)
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0

My version of the Comma Code:

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

def comma(aList):
    for i in range(len(aList) - 1):
        newList.append(aList[i])
    newList.append('and ')
    myString = ', '.join(newList)
    print(myString + aList[-1])

comma(spam)
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0

As per the assignment, you must make sure "your function should be able to work with any list value passed to it." That means it must work with 0, 1, 1+ list values.

spam = ['green','eggs','ham']

def merge(list):
    if len(list) == 0:
        return None
    elif len(list) == 1:
        return list[0]
    else:
        return ', '.join(list[:-1] + ['and '+list[-1]])

print(merge(spam))
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0

Here's pretty straightforward solution to the problem:

def lst2str(spam):
    str = ''
    for word in spam:
        if word != spam[-1]:
            spacing = word + ", "
            str += spacing
        else:
            spacing = "and " + word
            str += spacing
    return str
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