Recursion through List: Why is it returning None and giving separate lines?-CodePudding

I am figuring out a problem that goes through a list of strings, takes the first letter of each string and turns everything into an abbreviation of all the words in the list. So for example,

print(recAbbrev(['central','processing','unit']))

should return

'CPU'

Here is my code as of right now:

def recAbbrev(lst):
    'return a single string with the first character of all the strings in a list combined and capitalized.'
    if len(lst)==0:
        print('')
        return
    
    if len(lst)>0:
        if type(lst[0])==list:
            recAbbrev(lst[0])
        else:
            acronym = ""
            letter = ""
            letter = letter   lst[0][:1]
            letter = letter.upper()
            #lst.pop[0]
            acronym = acronym   letter
            print(acronym)  
            recAbbrev(lst[1:])

I am having two problems that I can't seem to understand with this code. First, I want my base case to return '' in the case of an empty list. Instead, it returns None. How can I work around this? Here is my output:

Starting recAbbrev

None
C
P
U

This is a simple question, but how can I get everything to stay on one line? It seems like recursion is trying to keep me from doing this.

CodePudding user response：

You are printing values and returning nothing. you have to modify you function:

def recAbbrev(lst):
    'return a single string with the first character of all the strings in a list combined and capitalized.'
    if len(lst)==0:
        return ''
    if len(lst)==1:
        return lst[0][0].upper()
    else:
        return lst[0][0].upper() recAbbrev(lst[1:])

then test it:

lst = ['central','processing','unit']

recAbbrev(lst)

CodePudding user response：

A simpler solution can be the following, unless you must use a recursion because this is a homework:

def recAbbrev(lst):
    return "".join([w[0].upper() for w in lst])

lst = ['central','processing','unit']
print(recAbbrev(lst))

Output:

CPU

This works also if the list is empty and in this case it returns en empty string.

CodePudding user response：

print has a default \n character at the end of the printed string (see the documentation here). Change print(acronym) to print(acronym, end='')

You are getting the None because you are printing recAbbrev, which has no return and therefore defaults to returning None. Just call recAbbrev(['central','processing','unit'])