cpython/Lib/_bootlocale.py

"""A minimal subset of the locale module used at interpreter startup
(imported by the _io module), in order to reduce startup time.

Don't import directly from third-party code; use the `locale` module instead!
"""

import sys
import _locale

if sys.platform.startswith("win"):
    def getpreferredencoding(do_setlocale=True):
        return _locale._getdefaultlocale()[1]
else:
    try:
        _locale.CODESET
    except AttributeError:
        if hasattr(sys, 'getandroidapilevel'):
            # On Android langinfo.h and CODESET are missing, and UTF-8 is
            # always used in mbstowcs() and wcstombs().
            def getpreferredencoding(do_setlocale=True):
                return 'UTF-8'
        else:
            def getpreferredencoding(do_setlocale=True):
                # This path for legacy systems needs the more complex
                # getdefaultlocale() function, import the full locale module.
                import locale
                return locale.getpreferredencoding(do_setlocale)
    else:
        def getpreferredencoding(do_setlocale=True):
            assert not do_setlocale
            result = _locale.nl_langinfo(_locale.CODESET)
            if not result and sys.platform == 'darwin':
                # nl_langinfo can return an empty string
                # when the setting has an invalid value.
                # Default to UTF-8 in that case because
                # UTF-8 is the default charset on OSX and
                # returning nothing will crash the
                # interpreter.
                result = 'UTF-8'
            return result