input: Write a function to port a given Java code snippet to Python 3. If the input code snippet is valid, return the Python 3 equivalent of the Java code snippet. If the input code snippet is invalid, return an error message.
  assert port_java_to_python("public class Foo { public int foo( int a, int b ) { return a + b; } }")=="def foo(a, b):\n return a + b"
  assert port_java_to_python("public class Bar { public String bar(String s) { return s + \" appended\"; } }")=="def bar(s):\n return s + \" appended\""
  assert port_java_to_python("public class Invalid { public void invalid() { // missing return statement } }")=="Error: Invalid Java code snippet"
  assert port_java_to_python("")=="Error: No Java code snippet provided"
output: def port_java_to_python(java_code):
      if not java_code:
          return "Error: No Java code snippet provided"
      
      import re
      match = re.search(r'public\s+class\s+\w+\s*\{\s*public\s+(\w+)\s+(\w+)\s*\(\s*(\w+)\s+(\w+)\s*(?:,\s*(\w+)\s+(\w+)\s*)?\)\s*\{\s*return\s+(.*?);\s*\}\s*\}', java_code)
      
      if not match:
          return "Error: Invalid Java code snippet"
      
      return_type, func_name, param1_type, param1_name, param2_type, param2_name, return_expr = match.groups()
      
      if param2_type is None:
          return f"def {func_name}({param1_name}):\n return {return_expr}"
      else:
          return f"def {func_name}({param1_name}, {param2_name}):\n return {return_expr}"