input: Write a python function to calculate the sum of two numbers and handle invalid input.
  assert calculate_sum("10", "20") == 30
  assert calculate_sum("5", "7") == 12
  assert calculate_sum("abc", "10") == "Please enter numbers"
  assert calculate_sum("10", "xyz") == "Please enter numbers"
output: def calculate_sum(a, b):
      try:
          return int(a) + int(b)
      except ValueError:
          return "Please enter numbers"