Global variables and recursion in python

Questions

In the following code, I ve tried to make a recursive function to find substrings of a given string.

i = 0
j = 0
def substrings(string):
    global i, j
    if j == len(string) - 1 or len(string) == 0:
        return []
    elif i == len(string):
        j = j + 1
        i = j + 1
        return [string[j:i]] + substrings(string)
    i += 1
    return [string[j:i]] + substrings(string)


>>> substrings( ceng )
>>> [ c ,  ce ,  cen ,  ceng ,  e ,  en ,  eng ,  n ,  ng ,  g ]

I always tend to use globals while working with recursions, and I don t like it at all. Is there anything I can do not to use globals in this case? I know I can pass the variables to the function as parameters, but it doesn t work for me since the function is supposed to have only one parameter.

Also, if there is a way of doing this without any variable at all, I d like to learn that too.

Answers

If you don t want to add any parameters to the function, you can enclose a second function within it:

def substrings(string):
    index= 0
    length= len(string)+1
    result= []

    def substrings(string, index):
        if index==length:
            return

        for i in xrange(index+1, length):
            result.append(string[index:i])
        substrings(string, index+1)
    substrings(string, index)

    return result

Source

License : cc by-sa 3.0

http://stackoverflow.com/questions/27342765/global-variables-and-recursion-in-python

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