ValidateInput.py

# Validating input in Python 3

validSymbolsInInt = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "-"]
validSymbolsInFloat = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "-", "."]


def readInt(number):
  charCounter = 0
  for num in number:
    charCounter += 1
    if not num in validSymbolsInInt:
      return False
    if (num == "-" and charCounter > 1) or (num == "-" and len(number) == 1):
      return False
    
  return number
  
def readFloat(number):
  numberOfDecPoints = 0
  charCounter = 0
  digits = validSymbolsInFloat[:10] # The valid digits
  numberString = ''.join(digits)

  # Are there any valid digits at all in input?
  matchFlag = 0
  for num in number:
    if numberString.find(num) != -1:
      matchFlag = 1
  if not matchFlag:
    return False
  
  # Other invalid chars in input?
  for num in number:
    charCounter += 1
    if not num in validSymbolsInFloat:
      return False
    elif num == ".":
      numberOfDecPoints += 1
      
    # Combinations and placements of valid chars may
    # make the input invalid.
    if (num == "-" and charCounter > 1) or ((num == "-" or num == ".") and len(number) == 1) or numberOfDecPoints > 1:
      return False

  # Return the valid number
  return number

numberInt = input("Enter an integer -> ")
while not readInt(numberInt):
  print("No integer, please try again.")
  numberInt = input("Enter an integer -> ")

numberInt = int(numberInt)

print("Success, you entered", numberInt)
print()

numberFloat = input("Enter a floating point number -> ")

while not readFloat(numberFloat):
  print("No number, please try again.")
  numberFloat = input("Enter a floating point number -> ")

numberFloat = float(numberFloat)

print("Success, you entered", numberFloat)