The following PR makes pickles for typing types more portable. Type variables no longer use _find_name() and can be unpickled in 3.6. Subscripted generics no longer expose internals and can be unpickled in 3.6 and future versions with changed internal implementation.Before this PR:>>> import pickle, pickletools, typing                                            >>> pickletools.dis(pickletools.optimize(pickle.dumps(typing.T, 4)))                  0: \x80 PROTO      4    2: \x95 FRAME      30   11: \x8c SHORT_BINUNICODE 'typing'   19: \x94 MEMOIZE    (as 0)   20: \x8c SHORT_BINUNICODE '_find_name'   32: \x93 STACK_GLOBAL   33: h    BINGET     0   35: \x8c SHORT_BINUNICODE 'T'   38: \x86 TUPLE2   39: R    REDUCE   40: .    STOPhighest protocol among opcodes = 4>>> pickletools.dis(pickletools.optimize(pickle.dumps(typing.Union[int, str], 4)))    0: \x80 PROTO      4    2: \x95 FRAME      198   11: \x8c SHORT_BINUNICODE 'copyreg'   20: \x8c SHORT_BINUNICODE '_reconstructor'   36: \x93 STACK_GLOBAL   37: \x8c SHORT_BINUNICODE 'typing'   45: \x94 MEMOIZE    (as 0)   46: \x8c SHORT_BINUNICODE '_GenericAlias'   61: \x93 STACK_GLOBAL   62: \x8c SHORT_BINUNICODE 'builtins'   72: \x94 MEMOIZE    (as 1)   73: \x8c SHORT_BINUNICODE 'object'   81: \x93 STACK_GLOBAL   82: N    NONE   83: \x87 TUPLE3   84: R    REDUCE   85: }    EMPTY_DICT   86: (    MARK   87: \x8c     SHORT_BINUNICODE '_inst'   94: \x88     NEWTRUE   95: \x8c     SHORT_BINUNICODE '_special'  105: \x89     NEWFALSE  106: \x8c     SHORT_BINUNICODE '_name'  113: N        NONE  114: \x8c     SHORT_BINUNICODE '__origin__'  126: h        BINGET     0  128: \x8c     SHORT_BINUNICODE 'Union'  135: \x93     STACK_GLOBAL  136: \x8c     SHORT_BINUNICODE '__args__'  146: h        BINGET     1  148: \x8c     SHORT_BINUNICODE 'int'  153: \x93     STACK_GLOBAL  154: h        BINGET     1  156: \x8c     SHORT_BINUNICODE 'str'  161: \x93     STACK_GLOBAL  162: \x86     TUPLE2  163: \x8c     SHORT_BINUNICODE '__parameters__'  179: )        EMPTY_TUPLE  180: \x8c     SHORT_BINUNICODE '__slots__'  191: N        NONE  192: \x8c     SHORT_BINUNICODE '__module__'  204: h        BINGET     0  206: u        SETITEMS   (MARK at 86)  207: b    BUILD  208: .    STOPhighest protocol among opcodes = 4With this PR:>>> import pickle, pickletools, typing                                                              >>> pickletools.dis(pickletools.optimize(pickle.dumps(typing.T, 4)))                           0: \x80 PROTO      4    2: \x95 FRAME      13   11: \x8c SHORT_BINUNICODE 'typing'   19: \x8c SHORT_BINUNICODE 'T'   22: \x93 STACK_GLOBAL   23: .    STOPhighest protocol among opcodes = 4>>> pickletools.dis(pickletools.optimize(pickle.dumps(typing.Union[int, str], 4)))           0: \x80 PROTO      4    2: \x95 FRAME      66   11: \x8c SHORT_BINUNICODE '_operator'   22: \x8c SHORT_BINUNICODE 'getitem'   31: \x93 STACK_GLOBAL   32: \x8c SHORT_BINUNICODE 'typing'   40: \x8c SHORT_BINUNICODE 'Union'   47: \x93 STACK_GLOBAL   48: \x8c SHORT_BINUNICODE 'builtins'   58: \x94 MEMOIZE    (as 0)   59: \x8c SHORT_BINUNICODE 'int'   64: \x93 STACK_GLOBAL   65: h    BINGET     0   67: \x8c SHORT_BINUNICODE 'str'   72: \x93 STACK_GLOBAL   73: \x86 TUPLE2   74: \x86 TUPLE2   75: R    REDUCE   76: .    STOPhighest protocol among opcodes = 4If there is a chance it would be nice to merge these changes into 3.7. Otherwise either pickles created in 3.7.0 will be incompatible not only with older Python versions, but with future Python versions too, or we will need to add complex code for supporting specific 3.7.0 pickles in future versions.

New changeset09f3221fbbf72692308149054e4f7668b08b22eb by Ivan Levkivskyi (Serhiy Storchaka) in branch 'master':bpo-33652: Improve pickle support in the typing module. (GH-7123)https://github.com/python/cpython/commit/09f3221fbbf72692308149054e4f7668b08b22eb

New changesetd49862582ed3513debed6e919fd4f92e9d4eebbd by Miss Islington (bot) in branch '3.7':bpo-33652: Improve pickle support in the typing module. (GH-7123)https://github.com/python/cpython/commit/d49862582ed3513debed6e919fd4f92e9d4eebbd

There is a question -- what to do with all these __getstate__ and __setstate__ methods? They are part of the pickle protocol, but they are not used when define __reduce__. And they are not needed for supporting compatibility with older versions, because in 3.6 pickleable generic types were pickled by name. I think it is better to remove these methods.

Yes, these are just legacy from times when TypeVars were serialized by value, not by identity like now. I think it should be safe to remove them. Would you like to make a PR?

New changeset97b523db7c79c18c48516fba9410014d9896abc4 by Ivan Levkivskyi (Serhiy Storchaka) in branch 'master':bpo-33652: Remove __getstate__ and __setstate__ methods in typing. (GH-7144)https://github.com/python/cpython/commit/97b523db7c79c18c48516fba9410014d9896abc4

New changeset98b089e2a178a309f20ac9ff498b230407da1f47 by Miss Islington (bot) in branch '3.7':bpo-33652: Remove __getstate__ and __setstate__ methods in typing. (GH-7144)https://github.com/python/cpython/commit/98b089e2a178a309f20ac9ff498b230407da1f47

I think this can be closed now.