This is really inefficient but:

>>> zero = ord("0")
>>> s = "1234"
>>> sum([x * 10**i for i, x in enumerate(map(lambda x: x - zero, map(ord, s))[::-1])])
1234

This is slightly better:

>>>> sum([x * 10**i for i, x in enumerate([ord(x) - zero for x in s[::-1]])])
1234

>>> atoi = lambda s: sum([x * 10**i for i, x in enumerate([ord(x) - zero for x in s[::-1]])])
>>> atoi("1234")
1234

You should avoid using iter as a variable name, since it happens to be the name of a built-in function. It's confusing to other Python programmers who have to read your code, and could produce a failure if you ever want to call the standard iter() function.

In any case, you don't want to have a clumsy loop that is based on char and also maintains iter. You certainly don't want an algorithm that puts an upper bound on the numbers you can handle. The standard algorithm goes like this:

CHAR_DIGIT = {'0':0, '1':1, '2':2, '3':3, '4':4, '5':5,  '6':6, '7':7, '8':8, '9':9}

def str2int(num_str):
    """
    Convert numeric string to number without using Python's built in functions.
    """
    number = 0
    for char in num_str:
        number = 10 * number + CHAR_DIGIT[char]
    return number

Maybe you were hoping for something like my_number = my_input.to_int. But it is not currently possible to do it natively. And funny enough, if you want to extract the integer part from a float-like string, you have to convert to float first, and then to int. Or else you get ValueError: invalid literal for int().

The robust way:

my_input = int(float(my_input))

For example:

>>> nb = "88.8"
>>> int(nb)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '88.8'
>>> int(float(nb))
88

I found this at https://www.geeksforgeeks.org/how-to-convert-string-to-integer-in-python/

# User-defined function to 
# convert a string into integer
def string_to_int(input_string):
    
  output_int = 0
    
  # Check if the number contains
  # any minus sign or not, 
  # i.e. is it a negative number or not. 
  # If it contains in the first
  # position in a minus sign,
  # we start our conversion 
  # from the second position which
  # contains numbers.
  if input_string[0] == '-' :
    starting_idx = 1
    check_negative = True
      
  else:
    starting_idx = 0
    check_negative = False
      
  for i in range(starting_idx, len(input_string)):
      
    # calculate the place value for 
    # the respective digit
    place_value = 10**(len(input_string) - (i+1))
      
    # calculate digit value
    # ord() function gives Ascii value
    digit_value = ord(input_string[i]) - ord('0')
      
    # calculating the final integer value
    output_int += place_value * digit_value
      
  # if check_negative is true 
  # then final integer value 
  # is multiplied by -1
  if check_negative :
    return -1 * output_int
  else:
    return output_int
  
# Driver code
if __name__ == "__main__" : 
    
  string = "554"
  
  # function call
  x = string_to_int(string)
  
  # Show the Data type
  print(type(x))
  
  string = "123"
  
  # Show the Data type
  print(type(string_to_int(string))) 
  
  string = "-123"
  
  # Show the Data type
  print(type(string_to_int(string)))

You can keep a dictionary that stores the string and integer values of a numeric key, and then iterate over the string. While iterating over the string, you can use enumerate to keep track of the index and then raise 10 to that power minus 1 and then multiply by the corresponding key from the dictionary:

a = "546"
length = 0
for i in a:
   length += 1
d = {'1': 1, '0': 0, '3': 3, '2': 2, '5': 5, '4': 4, '7': 7, '6': 6, '9': 9, '8': 8}
count = 0
counter = 0
for i in a:
   count += (10**(length-counter-1)*d[i])
   counter += 1
print(count)

Output:

546

Try this:

str(i)