python - how to print 1 string out of multiple string in a list

Question

I am having some trouble finding the solution for the "Join all exercise" in the Hands-on Python Tutorial of Andrew N. Harrington.

Basically, the exercise is to take a list like ['very', 'hot', 'day'] consisting only of strings, and to make one string out of it, in this case 'veryhotday'.

This is the exercise:

'''exercise to complete and test this function'''
def joinStrings(stringList):
    '''Join all the strings in stringList into one string,
    and return the result, NOT printing it. For example:
    >>> s = joinStrings(['very', 'hot', 'day'])
    >>> print(s)  # I can print s OUTSIDE joinStrings
    'veryhotday'
    '''
    # finish the code for this function

def main():
    print(joinStrings(['very', 'hot', 'day']))
    print(joinStrings(['this', 'is', 'it']))
    print(joinStrings(['1', '2', '3', '4', '5']))

main()

So only the first definition may be changed. I solved it like this:

def joinStrings(stringList):
    return ''.join(stringList)

and I believe this works and is correct. Correct me if I am wrong here, but the problem is that it has to be solved differently. I have to sort of accumulate the different strings. just as they show here with integers:

def sumList(nums):
    ’’’Return the sum of the numbers in the list nums.’’’
    sum = 0
    for num in nums:
        sum = sum + num
    return sum

and really I just can't figure it out, so please help me!

''.join(myList) is like sum(nums), and the best solution. If you have to do it longhand, you need to start with the empty string ''... — Andy Hayden
– Andy Hayden, Commented Sep 12, 2012 at 16:42

Kos · Accepted Answer · 2012-09-12 16:54:11Z

2

''.join(stringList) is the correct way. What is the problem?

If it has to be done differently, you could do one of:

import operator
return reduce(operator.add, stringList)

or even

s = ''
for string in stringList:
    s = s + string
return s

but that's unnecessary complication, since using join like you suggested is the simplest and preferred way. Probably also the fastest.

edited Sep 12, 2012 at 16:54

answered Sep 12, 2012 at 16:41

Kos

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4 Comments

user1666419 Over a year ago

that second suggestion is perfect! exactly what i was looking for. thx

Andy Hayden Over a year ago

Are you sure you can use sum like this, I get a TypeError: sum() takes no keyword arguments... ? Looking at docs, start can't be a string!

Kos Over a year ago

@hayden right, I didn't know that sum has a special case for strings (a bit surprising but reasonable since join is the way to go anyway)

Joran Beasley Over a year ago

reducing by operator.add is MUCH slower than ''.join ... orders of magnitude... see stackoverflow.com/a/3525380/541038

Nisan.H · Accepted Answer · 2012-09-12 16:42:22Z

2

Have a look at the str.join() method

''.join(['a','b','c']) # 'abc'
' '.join(['a','b','c']) # 'a b c'
print ' are '.join(['how', 'you']) # > how are you
s = ''.join(['%d'%i for i in range(10)]) # 01234567789

The str.join() function does not print anything, it simply creates a new string from a list of strings.

answered Sep 12, 2012 at 16:42

Nisan.H

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