Not quite getting the correct Output from a function

Not quite getting the correct Output from a function - Printable Version

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Not quite getting the correct Output from a function - twinpiques - Aug-01-2019

Hello.

I have a function that I'm trying to create.
When receiving a non-empty string input, I want to return a string containing every other character 2n+2 times.
(Where "n" is the 0-based index of the letter).

Example: input_string = "Rivers" #RRvvvvvvrrrrrrrrrr

def string_expansion( input_string ):
    n=0
    if len(input_string) == 0:
        return "invalid entry"
    #for n in range(len(input_string)):
    #    value = input_string[n::2]
    #    return value * (2*n+2)
    for n in range(0,len(input_string),2):
        #value = input_string[n]
        #strlen = len(input_string)
        print(value * (2*n+2))
    pass

input_string = "Rivers"
print(string_expansion(input_string))

I am getting:

Output:RR
vvvvvv
rrrrrrrrrr
None

I want to get:

Output:
RRvvvvvvrrrrrrrrrr

What am I goofing up here?

RE: Not quite getting the correct Output from a function - Yoriz - Aug-01-2019

Your code is printing the value per loop and not returning anything.
You need a container for your string before the loop, add to it inside the loop and return it after the loop.

RE: Not quite getting the correct Output from a function - perfringo - Aug-01-2019

If function doesn't return anything explicitly with return statement then it returns None (you can see it in your output: three lines printed and then None). In case of empty string function returns 'invalid entry' therefore there will be no None.

I would go for oneliner:

>>> s = 'Rivers'
>>> ''.join(char*(2*(i-1)+2) for i, char in enumerate(s, start=1) if i % 2)
'RRvvvvvvrrrrrrrrrr'

RE: Not quite getting the correct Output from a function - twinpiques - Aug-04-2019

Thank you for the replies. I tried both recommendations and they worked wonderfully...and I learned two different approaches in the process. Much appreciated!