Is there anyone that can help find the error in my Python program

Quote:

In my program, if I delete the return-1 statement I get the right answer but otherwise it keeps returning -1. Why does it keep doing so?

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
    #--- continue the rest of the code here ----#
    op=['+','-','*','/']
    for i in range(len(txt)):
        if txt[i] in op:
            return(i)
        else:
    return(-1)
            
        
        
print(findNextOpr("1+2+3"))