How do I find the leftmost number and/or operator in a string. The string is an arithmetic expression.

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Python

Python3.6

Suppose a string is "1+2-3/4*5"
If I give the position as 2. Then how do I return the value 2 for the leftmost number and - for the leftmost operator

What I have tried:

I have found out for operator. But I need help for string.

op=['+','-','*','/']
    
    for i in range(len(txt)):
        if txt[i] in op:
            return(i)
            break
    else:
        return(-1)