This part of a program, I have to do. I have to take a string\"s\", which for ex

Question

This part of a program, I have to do. I have to take a string"s", which for example might be s= " 3 * 5 + 1 " and properly calculate it. I need some help getting started, thanks. Also in python 3.6

def getNextNumber(expr, pos):
#expr is a given arithmetic formula in string s
#pos = start position in expr
#1st returned value = the next number (None if N/A)
#2nd returned value = the next operator (None if N/A)
#3rd retruned value = the next operator position (None if N/A)
if len(expr)==0 or not isinstance(expr, str) or pos<0 or pos>=len(expr) or not isinstance(pos, int):
print("type mismatch error: getNextNumber")
return None, None, "type mismatch error: getNextNumber"
#--- function code starts ---#

#--- function code ends ---#

Explanation / Answer

#--- function code starts ---#

def getNextNumber(expr,pos):
if len(expr)==0 or not isinstance(expr,str) or not isinstance(pos,int):
    print("type mismatch error: getNextNumber")
    return (None,None,"type mismatch error: getNextNumber")
elif pos<=0 or pos>=len(expr):
    print("type mismatch error: getNextNumber")
    return (None,None,"type mismatch error: getNextNumber")
else:
    #print ("position",expr.index(pos))
    return (pos)
  
#--- function code ends ---#

s = input('Please enter expression')
s= " 3 * 5 + 1 "

for letter in s:
print (letter,s.index(letter))
res=getNextNumber(s,s.index(letter))

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