header.py 文件源码

def encode(self, splitchars=';, '):
        """Encode a message header into an RFC-compliant format.

        There are many issues involved in converting a given string for use in
        an email header.  Only certain character sets are readable in most
        email clients, and as header strings can only contain a subset of
        7-bit ASCII, care must be taken to properly convert and encode (with
        Base64 or quoted-printable) header strings.  In addition, there is a
        75-character length limit on any given encoded header field, so
        line-wrapping must be performed, even with double-byte character sets.

        This method will do its best to convert the string to the correct
        character set used in email, and encode and line wrap it safely with
        the appropriate scheme for that character set.

        If the given charset is not known or an error occurs during
        conversion, this function will return the header untouched.

        Optional splitchars is a string containing characters to split long
        ASCII lines on, in rough support of RFC 2822's `highest level
        syntactic breaks'.  This doesn't affect RFC 2047 encoded lines.
        """
        newchunks = []
        maxlinelen = self._firstlinelen
        lastlen = 0
        for s, charset in self._chunks:
            # The first bit of the next chunk should be just long enough to
            # fill the next line.  Don't forget the space separating the
            # encoded words.
            targetlen = maxlinelen - lastlen - 1
            if targetlen < charset.encoded_header_len(''):
                # Stick it on the next line
                targetlen = maxlinelen
            newchunks += self._split(s, charset, targetlen, splitchars)
            lastchunk, lastcharset = newchunks[-1]
            lastlen = lastcharset.encoded_header_len(lastchunk)
        value = self._encode_chunks(newchunks, maxlinelen)
        if _embeded_header.search(value):
            raise HeaderParseError("header value appears to contain "
                "an embedded header: {!r}".format(value))
        return value