"cannot concatenate 'str' and 'int' objects" error

Question

I keep getting a "cannot concatenate 'str' and 'int' objects" error when I try to run the following code. I'm pointed to line 6 as the source of the problem, but I really can't see the error! My types all seem to be consistent.

def DashInsert(num): 
  num_str = str(num)
  new_str = ''

  for i in num_str:
    var1 = num_str[i:i+1]
    var2 = num_str[i+1:i+2]

    if var1 % 2 == 1 and var2 % 2 == 1:
      new_str = new_str + num_str[i:i+1] + "-"
    else:
      new_str = new_str + num_str[i:i+1]

  return new_str

# keep this function call here  
# to see how to enter arguments in Python scroll down
print DashInsert(raw_input())  

Answer 1

for i in num_str:

i is not an index in this case, it is a string character.

For example, if num in your code is 42, the work flow will be:

num_str = str(42) # '42'
for i in num_str: # First iteration
    var1 = num_str['4':'4'+1] # Python: '4' + 1 = ERROR

What you are probably looking for is:

for i, c in enumerate(num_str):
    var1 = num_str[0:0+1] # Python: 0 + 1 = 1

See this answer.