input: Write a function to concatenate two string variables and print them in the same line. The function should return the concatenated string. If either of the input strings is empty, the function should return an empty string.
  assert concatenate_and_print("Hello", "World")=="Hello World"
  assert concatenate_and_print("", "World")==""
  assert concatenate_and_print("Hello", "")==""
  assert concatenate_and_print("", "")==""
output: def concatenate_and_print(str1, str2):
      if not str1 or not str2:
          return ""
      return str1 + " " + str2