recursion used to convert string into sum

[fred1232]

Recursive Python

I am trying to learn recursive programming in Python by reading a GitHub document titled “Understanding Recursion Using Python ” subtitled, “A shamelessly verbose guide to the wonders of recursion”. The document is contributed by -- © Copyright 2019, panopticonopolis.

I have done the suggested exercises which work as desired, but I would very much like to see how others are coding the same exercises. So if possible I would like to correspond with other students who are using this document as a learning tool.

I am posting the last exercise I coded. It takes a string of digits and converts them to an integer sum using recursion. The code works, but I think there is likely a more elegant, efficient way to do it. The area where I think this code fails is that it doesn’t really use the post recursive code to arrive at the answer. I would appreciate a hint to fix this. The code is heavily annotated per the exercise instructions.

I am using Python 3.9 with Pycharm Community Edition 2021.2 running Windows 10 Home.

I am new to python-forum. Is this post correctly posted to this forum?

summ = 0
frame = 0
""" s is the test string """
def stoi(s, n):
    global summ, frame
    if frame == 0:
        print()
        print('  in global frame=0    s= string' , s, '    summ=0      n=0' )
    if n < len(s):
        frame += 1
        print()
        print('  in recur frame =', frame)
        print('    rcvd:  s= ', s, '   summ=', summ,   '    n= ', n)
        summ = int(s[n]) + summ
        print('    passed:    s= ', s , '    summ=', summ, '    n= ', n+1)
# the base case is reached when n=len(s)
    elif n == len(s):
        print()
        print('  in base frame', frame+1, '  s= ', s , '    summ=', summ, '    n= ', n+1)
    else:
        print()
        print('  in outcur frame =', frame)
        print('     s= ', s,'    summ=', summ,  '   n= ', n, )
        frame -= 1
        if frame == 0:
            return
    stoi(s, n + 1)
stoi(str(473), 0)

Output:
C:\Users\sfn22\AppData\Local\Programs\Python\Python39\python.exe "C:\Program Files\JetBrains\PyCharm Community Edition 2021.2\plugins\python-ce\helpers\pydev\pydevd.py" --multiproc --qt-support=auto --client 127.0.0.1 --port 50168 --file "C:/Users/sfn22/PycharmProjects/Pythonbook_2108/Chpt. 5/convert a string of digits to an integer sum.py"
Connected to pydev debugger (build 212.4746.96)

  in global frame=0    s= string 473     summ=0      n=0

  in recur frame = 1
    rcvd:  s=  473    summ= 0     n=  0
    passed:    s=  473     summ= 4     n=  1

  in recur frame = 2
    rcvd:  s=  473    summ= 4     n=  1
    passed:    s=  473     summ= 11     n=  2

  in recur frame = 3
    rcvd:  s=  473    summ= 11     n=  2
    passed:    s=  473     summ= 14     n=  3

  in base frame 4   s=  473     summ= 14     n=  4

  in outcur frame = 3
     s=  473     summ= 14    n=  4

  in outcur frame = 2
     s=  473     summ= 14    n=  5

  in outcur frame = 1
     s=  473     summ= 14    n=  6

Process finished with exit code 0