input: Write a function to port a Java code snippet to Python 3. If the given Java code snippet is valid, return the equivalent Python code. If the Java code is invalid or cannot be ported, return an empty string.
  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 int bar( int x ) { return x * 2; } }") == "def bar(x):\n return x * 2"
  assert port_java_to_python("public class Invalid { public void invalid() { } }") == ""
  assert port_java_to_python("") == ""
output: def port_java_to_python(java_code):
      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+(\w+)\s*([+\-*/])\s*(\w+)\s*;\s*\}\s*\}', java_code)
      if match:
          return_type, method_name, param1_type, param1_name, param2_type, param2_name, var1, operator, var2 = match.groups()
          if param2_type is None:
              return f"def {method_name}({param1_name}):\n return {var1} {operator} {var2}"
          else:
              return f"def {method_name}({param1_name}, {param2_name}):\n return {var1} {operator} {var2}"
      return ""