我的程序有错误，无法找出它不起作用的原因

Question

def findNextOpr(txt):
        #txt must be a nonempty string. 
        if len(txt)<=0 or not isinstance(txt,str):
               print("type error: findNextOpr")
               return "type error: findNextOpr"
#In this exercise +, -, *, / are all the 4 operators
#The function returns -1 if there is no operator in txt,
#otherwise returns the position of the leftmost operator

        op=['+','-','*','/']
        for i in range(len(txt)):
               if txt[i] in op:
                   return(i)
               else:
                   return(-1)#this is the else statement I keep getting the worng answer with

print(findNextOpr("1+2+3"))

The indentation is not perfect but I keep getting the value -1. I tried removing the else statement and then the program runs perfectly. But I need the -1 to be returned if there is not operator in txt. What is the error in my program? I am a newbie to Python. So please spare the hate.

Answer 1

When I run this code I get the intended result, 1. My guess is that the else statement after the for loop is slid in, so is executed if the first symbol isn't an op.

def findNextOpr(txt):
        #txt must be a nonempty string.
        if len(txt)<=0 or not isinstance(txt,str):
                print("type error: findNextOpr")
                return "type error: findNextOpr"

        op=['+','-','*','/']
        for i in range(len(txt)):
                if txt[i] in op:
                        print(txt[i])
                        return(i)
        else:
                return(-1)#this is the else statement I keep getting the worng answer with

print(findNextOpr("1+2+3"))