if classdict multipleraise typeerror("multiple definitions exist"return type _new_ (cls,name,bases,classdictif you apply this metaclass to another class definitionit will report an error if any method is redefined for exampleclass foo(metaclass=multimeta)def _init_ (self)pass def _init_ (self, )pass error _init_ multiply defined common pitfalls if you are migrating from python to be aware that python is more than just new syntax and language features major parts of the core language and library have been reworked in ways that are sometimes subtle there are aspects of python that may seem like bugs to python programmer in other casesthings that used to be "easyin python are now forbidden this section outlines some of the most major pitfalls that are likely to be encountered by python programmers making the switch text versus bytes python makes very strict distinction between text strings (charactersand binary data (bytesa literal such as "hellorepresents text string stored as unicodewhereas "hellorepresents string of bytes (containing ascii letters in this caseunder no circumstances can the str and bytes type be mixed in python for exampleif you try to concatenate strings and bytes togetheryou will get typeerror exception this differs from python where byte strings would be automatically coerced into unicode as needed to convert text string into bytesyou must use encode(encodingfor examples encode('utf- 'converts into utf- encoded byte string to convert byte string back into textyou must use decode(encodingyou can view the encode(and decode(methods as kind of "type castbetween strings and bytes keeping clean separation between text and bytes is ultimately good thing--the rules for mixing string types in python were obscure and difficult to understand at best howeverone consequence of the python approach is that byte strings are much more restricted in their ability to actually behave like "text although there are the standard string methods like split(and replace()other aspects of byte strings are not the same as in python for instanceif you print byte stringyou simply get its repr(output with quotes such as 'contentssimilarlynone of the string formatting operations (%format()work for examplex 'hello worldprint(xprint( "you said '% 'xproduces 'hello worldtypeerroroperator not supported the loss of text-like behavior with bytes is potential pitfall for system programmers despite the invasion of unicodethere are many cases where one actually does want to lib fl ff