Ezio Melotti <report@bugs.python.org> wrote
   on Tue, 16 Aug 2011 09:23:50 -0000: 

> All the other macros[0] follow the same convention, e.g. Py_UNICODE_ISLOWER
> and Py_UNICODE_TOLOWER.  I agree that keeping the words separate makes them
> more readable though.

> 	[0]: Include/unicodeobject.h:328

I am guessing that that is not quite why those don't have underscores
in them.  I bet it is actually something else.  Watch:

    % unigrep '^\s*#\s*define\s+Py_[\p{Lu}_]+\b' unicodeobject.h
    #define Py_UNICODEOBJECT_H
    #define Py_USING_UNICODE
    #define Py_UNICODE_WIDE
    #define Py_UNICODE_ISSPACE(ch) \
    #define Py_UNICODE_ISLOWER(ch) _PyUnicode_IsLowercase(ch)
    #define Py_UNICODE_ISUPPER(ch) _PyUnicode_IsUppercase(ch)
    #define Py_UNICODE_ISTITLE(ch) _PyUnicode_IsTitlecase(ch)
    #define Py_UNICODE_ISLINEBREAK(ch) _PyUnicode_IsLinebreak(ch)
    #define Py_UNICODE_TOLOWER(ch) _PyUnicode_ToLowercase(ch)
    #define Py_UNICODE_TOUPPER(ch) _PyUnicode_ToUppercase(ch)
    #define Py_UNICODE_TOTITLE(ch) _PyUnicode_ToTitlecase(ch)
    #define Py_UNICODE_ISDECIMAL(ch) _PyUnicode_IsDecimalDigit(ch)
    #define Py_UNICODE_ISDIGIT(ch) _PyUnicode_IsDigit(ch)
    #define Py_UNICODE_ISNUMERIC(ch) _PyUnicode_IsNumeric(ch)
    #define Py_UNICODE_ISPRINTABLE(ch) _PyUnicode_IsPrintable(ch)
    #define Py_UNICODE_TODECIMAL(ch) _PyUnicode_ToDecimalDigit(ch)
    #define Py_UNICODE_TODIGIT(ch) _PyUnicode_ToDigit(ch)
    #define Py_UNICODE_TONUMERIC(ch) _PyUnicode_ToNumeric(ch)
    #define Py_UNICODE_ISALPHA(ch) _PyUnicode_IsAlpha(ch)
    #define Py_UNICODE_ISALNUM(ch) \
    #define Py_UNICODE_COPY(target, source, length)                         \
    #define Py_UNICODE_FILL(target, value, length) \
    #define Py_UNICODE_MATCH(string, offset, substring) \
    #define Py_UNICODE_REPLACEMENT_CHARACTER ((Py_UNICODE) 0xFFFD)

It looks like what is actually happening there is that you started out
with names of the normal ctype(3) macroish thingies:

     isalpha isupper islower isdigit isxdigit isalnum isspace ispunct
     isprint isgraph iscntrl isblank isascii  toupper isblank isascii
     toupper tolower toascii

and wanted to preserve those, which would lead to Py_UNICODE_TOLOWER and
Py_UNICODE_TOUPPER, since there are no functions in the original C versions
those seem to mirror.  Then when you wanted more of that ilk, you sensibly
kept to the same naming convention.

I eyeball few exceptions to that style here:

    % perl -nle '/^\s*#\s*define\s+(Py_[\p{Lu}_]+)\b/ and print $1' Include/*.h | sort -dfu | fmt -150
    Py_ABSTRACTOBJECT_H Py_ALIGNED Py_ALLOW_RECURSION Py_ARITHMETIC_RIGHT_SHIFT Py_ASDL_H Py_AST_H Py_ATOMIC_H Py_BEGIN_ALLOW_THREADS Py_BITSET_H
    Py_BLOCK_THREADS Py_BLTINMODULE_H Py_BOOLOBJECT_H Py_BYTEARRAYOBJECT_H Py_BYTES_CTYPE_H Py_BYTESOBJECT_H Py_CAPSULE_H Py_CELLOBJECT_H Py_CEVAL_H
    Py_CHARMASK Py_CLASSOBJECT_H Py_CLEANUP_SUPPORTED Py_CLEAR Py_CODECREGISTRY_H Py_CODE_H Py_COMPILE_H Py_COMPLEXOBJECT_H Py_CURSES_H Py_DECREF
    Py_DEPRECATED Py_DESCROBJECT_H Py_DICTOBJECT_H Py_DTSF_ALT Py_DTSF_SIGN Py_DTST_FINITE Py_DTST_INFINITE Py_DTST_NAN Py_END_ALLOW_RECURSION
    Py_END_ALLOW_THREADS Py_ENUMOBJECT_H Py_EQ Py_ERRCODE_H Py_ERRORS_H Py_EVAL_H Py_FILEOBJECT_H Py_FILEUTILS_H Py_FLOATOBJECT_H Py_FORCE_DOUBLE
    Py_FORCE_EXPANSION Py_FORMAT_PARSETUPLE Py_FRAMEOBJECT_H Py_FUNCOBJECT_H Py_GCC_ATTRIBUTE Py_GE Py_GENOBJECT_H Py_GETENV Py_GRAMMAR_H Py_GT
    Py_HUGE_VAL Py_IMPORT_H Py_INCREF Py_INTRCHECK_H Py_INVALID_SIZE Py_ISALNUM Py_ISALPHA Py_ISDIGIT Py_IS_FINITE Py_IS_INFINITY Py_ISLOWER Py_IS_NAN
    Py_ISSPACE Py_ISUPPER Py_ISXDIGIT Py_ITEROBJECT_H Py_LE Py_LISTOBJECT_H Py_LL Py_LOCAL Py_LOCAL_INLINE Py_LONGINTREPR_H Py_LONGOBJECT_H Py_LT
    Py_MARSHAL_H Py_MARSHAL_VERSION Py_MATH_E Py_MATH_PI Py_MEMCPY Py_MEMORYOBJECT_H Py_METAGRAMMAR_H Py_METHODOBJECT_H Py_MODSUPPORT_H Py_MODULEOBJECT_H
    Py_NAN Py_NE Py_NODE_H Py_OBJECT_H Py_OBJIMPL_H Py_OPCODE_H Py_OSDEFS_H Py_OVERFLOWED Py_PARSETOK_H Py_PGEN_H Py_PGENHEADERS_H Py_PRINT_RAW
    Py_PYARENA_H Py_PYDEBUG_H Py_PYFPE_H Py_PYGETOPT_H Py_PYMATH_H Py_PYMEM_H Py_PYPORT_H Py_PYSTATE_H Py_PYTHON_H Py_PYTHONRUN_H Py_PYTHREAD_H
    Py_PYTIME_H Py_RANGEOBJECT_H Py_REFCNT Py_REF_DEBUG Py_RETURN_FALSE Py_RETURN_INF Py_RETURN_NAN Py_RETURN_NONE Py_RETURN_TRUE Py_SAFE_DOWNCAST
    Py_SET_ERANGE_IF_OVERFLOW Py_SET_ERRNO_ON_MATH_ERROR Py_SETOBJECT_H Py_SIZE Py_SLICEOBJECT_H Py_STRCMP_H Py_STRTOD_H Py_STRUCTMEMBER_H Py_STRUCTSEQ_H
    Py_SYMTABLE_H Py_SYSMODULE_H Py_TOKEN_H Py_TOLOWER Py_TOUPPER Py_TPFLAGS_BASE_EXC_SUBCLASS Py_TPFLAGS_BASETYPE Py_TPFLAGS_BYTES_SUBCLASS
    Py_TPFLAGS_DEFAULT Py_TPFLAGS_DICT_SUBCLASS Py_TPFLAGS_HAVE_GC Py_TPFLAGS_HAVE_STACKLESS_EXTENSION Py_TPFLAGS_HAVE_VERSION_TAG Py_TPFLAGS_HEAPTYPE
    Py_TPFLAGS_INT_SUBCLASS Py_TPFLAGS_IS_ABSTRACT Py_TPFLAGS_LIST_SUBCLASS Py_TPFLAGS_LONG_SUBCLASS Py_TPFLAGS_READY Py_TPFLAGS_READYING
    Py_TPFLAGS_TUPLE_SUBCLASS Py_TPFLAGS_TYPE_SUBCLASS Py_TPFLAGS_UNICODE_SUBCLASS Py_TPFLAGS_VALID_VERSION_TAG Py_TRACEBACK_H Py_TRACE_REFS
    Py_TRASHCAN_SAFE_BEGIN Py_TRASHCAN_SAFE_END Py_TUPLEOBJECT_H Py_TYPE Py_UCNHASH_H Py_ULL Py_UNBLOCK_THREADS Py_UNICODE_COPY Py_UNICODE_FILL
    Py_UNICODE_ISALNUM Py_UNICODE_ISALPHA Py_UNICODE_ISDECIMAL Py_UNICODE_ISDIGIT Py_UNICODE_ISLINEBREAK Py_UNICODE_ISLOWER Py_UNICODE_ISNUMERIC
    Py_UNICODE_ISPRINTABLE Py_UNICODE_ISSPACE Py_UNICODE_ISTITLE Py_UNICODE_ISUPPER Py_UNICODE_MATCH Py_UNICODEOBJECT_H Py_UNICODE_REPLACEMENT_CHARACTER
    Py_UNICODE_TODECIMAL Py_UNICODE_TODIGIT Py_UNICODE_TOLOWER Py_UNICODE_TONUMERIC Py_UNICODE_TOTITLE Py_UNICODE_TOUPPER Py_UNICODE_WIDE Py_USING_UNICODE
    Py_VA_COPY Py_VISIT Py_WARNINGS_H Py_WEAKREFOBJECT_H Py_XDECREF Py_XINCREF

See what I mean?    Most of them that remain tend to be things that one could
construe as compound words, like "RANGEOBJECT" or "CODEREGISTRY",  though some
people might find a few a bit on the longish side to read unaided by
underscores, like "BYTEARRAYOBJECT".

'Nuff bikeshedding. :)

--tom