input: Write a python function to remove non-alphanumeric characters from a given string.
  assert process_text("Hello, World!") == "HelloWorld"
  assert process_text("123@#45!67") == "1234567"
  assert process_text("Python_3.8") == "Python38"
output: def process_text(s: str) -> str:
      return ''.join(char for char in s if char.isalnum())