input: Write a function to validate a decimal number with a precision of 2.
  assert is_decimal('123.11')==True
  assert is_decimal('e666.86')==False
  assert is_decimal('3.124587')==False
output: def is_decimal(number_str):
      try:
          parts = number_str.split('.')
          if len(parts) != 2:
              return False
          if len(parts[1]) != 2:
              return False
          float(number_str)
          return True
      except ValueError:
          return False