# documentação Django 2.0.8

# Código fonte para django.utils.encoding

    import codecs
    import datetime
    import locale
    from decimal import Decimal
    from urllib.parse import quote

    from django.utils import six
    from django.utils.functional import Promise

    class DjangoUnicodeDecodeError(UnicodeDecodeError):
        def __init__(self, obj, *args):
            self.obj = obj
            super().__init__(*args)

        def __str__(self):
            return '%s. You passed in %r (%s)' % (super().__str__(), self.obj, type(self.obj))

    # For backwards compatibility. (originally in Django, then added to six 1.9)
    python_2_unicode_compatible = six.python_2_unicode_compatible

    def smart_text(s, encoding='utf-8', strings_only=False, errors='strict'):
        """
        Return a string representing 's'. Treat bytestrings using the 'encoding'
        codec.

        If strings_only is True, don't convert (some) non-string-like objects.
        """
        if isinstance(s, Promise):
            # The input is the result of a gettext_lazy() call.
            return s
        return force_text(s, encoding, strings_only, errors)

    _PROTECTED_TYPES = (
        type(None), int, float, Decimal, datetime.datetime, datetime.date, datetime.time,
    )

    def is_protected_type(obj):
        """Determine if the object instance is of a protected type.

        Objects of protected types are preserved as-is when passed to
        force_text(strings_only=True).
        """
        return isinstance(obj, _PROTECTED_TYPES)

    def force_text(s, encoding='utf-8', strings_only=False, errors='strict'):
        """
        Similar to smart_text, except that lazy instances are resolved to
        strings, rather than kept as lazy objects.

        If strings_only is True, don't convert (some) non-string-like objects.
        """
        # Handle the common case first for performance reasons.
        if issubclass(type(s), str):
            return s
        if strings_only and is_protected_type(s):
            return s
        try:
            if isinstance(s, bytes):
                s = str(s, encoding, errors)
            else:
                s = str(s)
        except UnicodeDecodeError as e:
            raise DjangoUnicodeDecodeError(s, *e.args)
        return s

    def smart_bytes(s, encoding='utf-8', strings_only=False, errors='strict'):
        """
        Return a bytestring version of 's', encoded as specified in 'encoding'.

        If strings_only is True, don't convert (some) non-string-like objects.
        """
        if isinstance(s, Promise):
            # The input is the result of a gettext_lazy() call.
            return s
        return force_bytes(s, encoding, strings_only, errors)

    def force_bytes(s, encoding='utf-8', strings_only=False, errors='strict'):
        """
        Similar to smart_bytes, except that lazy instances are resolved to
        strings, rather than kept as lazy objects.

        If strings_only is True, don't convert (some) non-string-like objects.
        """
        # Handle the common case first for performance reasons.
        if isinstance(s, bytes):
            if encoding == 'utf-8':
                return s
            else:
                return s.decode('utf-8', errors).encode(encoding, errors)
        if strings_only and is_protected_type(s):
            return s
        if isinstance(s, memoryview):
            return bytes(s)
        if isinstance(s, Promise) or not isinstance(s, str):
            return str(s).encode(encoding, errors)
        else:
            return s.encode(encoding, errors)

    smart_str = smart_text
    force_str = force_text

    smart_str.__doc__ = """
    Apply smart_text in Python 3 and smart_bytes in Python 2.

    This is suitable for writing to sys.stdout (for instance).
    """

    force_str.__doc__ = """
    Apply force_text in Python 3 and force_bytes in Python 2.
    """

    def iri_to_uri(iri):
        """
        Convert an Internationalized Resource Identifier (IRI) portion to a URI
        portion that is suitable for inclusion in a URL.

        This is the algorithm from section 3.1 of RFC 3987, slightly simplified
        since the input is assumed to be a string rather than an arbitrary byte
        stream.

        Take an IRI (string or UTF-8 bytes, e.g. '/I ♥ Django/' or
        b'/I \xe2\x99\xa5 Django/') and return a string containing the encoded
        result with ASCII chars only (e.g. '/I%20%E2%99%A5%20Django/').
        """
        # The list of safe characters here is constructed from the "reserved" and
        # "unreserved" characters specified in sections 2.2 and 2.3 of RFC 3986:
        #     reserved    = gen-delims / sub-delims
        #     gen-delims  = ":" / "/" / "?" / "#" / "[" / "]" / "@"
        #     sub-delims  = "!" / "$" / "&" / "'" / "(" / ")"
        #                   / "*" / "+" / "," / ";" / "="
        #     unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"
        # Of the unreserved characters, urllib.parse.quote() already considers all
        # but the ~ safe.
        # The % character is also added to the list of safe characters here, as the
        # end of section 3.1 of RFC 3987 specifically mentions that % must not be
        # converted.
        if iri is None:
            return iri
        elif isinstance(iri, Promise):
            iri = str(iri)
        return quote(iri, safe="/#%[]=:;$&()+,!?*@'~")

    # List of byte values that uri_to_iri() decodes from percent encoding.
    # First, the unreserved characters from RFC 3986:
    _ascii_ranges = [[45, 46, 95, 126], range(65, 91), range(97, 123)]
    _hextobyte = {
        (fmt % char).encode(): bytes((char,))
        for ascii_range in _ascii_ranges
        for char in ascii_range
        for fmt in ['%02x', '%02X']
    }
    # And then everything above 128, because bytes ≥ 128 are part of multibyte
    # unicode characters.
    _hexdig = '0123456789ABCDEFabcdef'
    _hextobyte.update({
        (a + b).encode(): bytes.fromhex(a + b)
        for a in _hexdig[8:] for b in _hexdig
    })

    def uri_to_iri(uri):
        """
        Convert a Uniform Resource Identifier(URI) into an Internationalized
        Resource Identifier(IRI).

        This is the algorithm from section 3.2 of RFC 3987, excluding step 4.

        Take an URI in ASCII bytes (e.g. '/I%20%E2%99%A5%20Django/') and return
        a string containing the encoded result (e.g. '/I%20♥%20Django/').
        """
        if uri is None:
            return uri
        uri = force_bytes(uri)
        # Fast selective unqote: First, split on '%' and then starting with the
        # second block, decode the first 2 bytes if they represent a hex code to
        # decode. The rest of the block is the part after '%AB', not containing
        # any '%'. Add that to the output without further processing.
        bits = uri.split(b'%')
        if len(bits) == 1:
            iri = uri
        else:
            parts = [bits[0]]
            append = parts.append
            hextobyte = _hextobyte
            for item in bits[1:]:
                hex = item[:2]
                if hex in hextobyte:
                    append(hextobyte[item[:2]])
                    append(item[2:])
                else:
                    append(b'%')
                    append(item)
            iri = b''.join(parts)
        return repercent_broken_unicode(iri).decode()

    def escape_uri_path(path):
        """
        Escape the unsafe characters from the path portion of a Uniform Resource
        Identifier (URI).
        """
        # These are the "reserved" and "unreserved" characters specified in
        # sections 2.2 and 2.3 of RFC 2396:
        #   reserved    = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" | "$" | ","
        #   unreserved  = alphanum | mark
        #   mark        = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"
        # The list of safe characters here is constructed subtracting ";", "=",
        # and "?" according to section 3.3 of RFC 2396.
        # The reason for not subtracting and escaping "/" is that we are escaping
        # the entire path, not a path segment.
        return quote(path, safe="/:@&+$,-_.!~*'()")

    def repercent_broken_unicode(path):
        """
        As per section 3.2 of RFC 3987, step three of converting a URI into an IRI,
        repercent-encode any octet produced that is not part of a strictly legal
        UTF-8 octet sequence.
        """
        try:
            path.decode()
        except UnicodeDecodeError as e:
            repercent = quote(path[e.start:e.end], safe=b"/#%[]=:;$&()+,!?*@'~")
            path = repercent_broken_unicode(
                path[:e.start] + force_bytes(repercent) + path[e.end:])
        return path

    def filepath_to_uri(path):
        """Convert a file system path to a URI portion that is suitable for
        inclusion in a URL.

        Encode certain chars that would normally be recognized as special chars
        for URIs. Do not encode the ' character, as it is a valid character
        within URIs. See the encodeURIComponent() JavaScript function for details.
        """
        if path is None:
            return path
        # I know about `os.sep` and `os.altsep` but I want to leave
        # some flexibility for hardcoding separators.
        return quote(path.replace("\\", "/"), safe="/~!*()'")

    def get_system_encoding():
        """
        The encoding of the default system locale. Fallback to 'ascii' if the
        #encoding is unsupported by Python or could not be determined. See tickets
        #10335 and #5846.
        """
        try:
            encoding = locale.getdefaultlocale()[1] or 'ascii'
            codecs.lookup(encoding)
        except Exception:
            encoding = 'ascii'
        return encoding

    DEFAULT_LOCALE_ENCODING = get_system_encoding()