[Python编程(第4版)].(Programming.Python.4th.Edition).Mark.Lutz.文字版

>>> m = MIMEText('abc', _charset='ascii') # pass text for ascii

>>> print(m)

MIME-Version: 1.0

Content-Type: text/plain; charset="us-ascii"

Content-Transfer-Encoding: 7bit

abc

>>> m = MIMEText('abc', _charset='latin-1') # pass text for latin-1

>>> print(m) # but not for 'latin1': ahead

MIME-Version: 1.0

Content-Type: text/plain; charset="iso-8859-1"

Content-Transfer-Encoding: quoted-printable

abc

>>> m = MIMEText(b'abc', _charset='utf-8') # pass bytes for utf8

>>> print(m)

Content-Type: text/plain; charset="utf-8"

MIME-Version: 1.0

Content-Transfer-Encoding: base64

YWJj

This works, but if you look closely, you’ll notice that we must pass str to the first two,
but bytes to the third. That requires that we special-case code for Unicode types based
upon the package’s internal operation. Types other than those expected for a Unicode
encoding don’t work at all, because of newly invalid str/bytes combinations that occur
inside the email package in 3.1:

>>> m = MIMEText('abc', _charset='ascii')

>>> m = MIMEText(b'abc', _charset='ascii') # bug: assumes 2.X str

Traceback (most recent call last):

...lines omitted...

File "C:\Python31\lib\email\encoders.py", line 60, in encode_7or8bit

orig.encode('ascii')

AttributeError: 'bytes' object has no attribute 'encode'

>>> m = MIMEText('abc', _charset='latin-1')

>>> m = MIMEText(b'abc', _charset='latin-1') # bug: qp uses str

Traceback (most recent call last):

...lines omitted...

File "C:\Python31\lib\email\quoprimime.py", line 176, in body_encode

if line.endswith(CRLF):

TypeError: expected an object with the buffer interface

>>> m = MIMEText(b'abc', _charset='utf-8')

>>> m = MIMEText('abc', _charset='utf-8') # bug: base64 uses bytes

Traceback (most recent call last):

...lines omitted...

File "C:\Python31\lib\email\base64mime.py", line 94, in body_encode

enc = b2a_base64(s[i:i + max_unencoded]).decode("ascii")

TypeError: must be bytes or buffer, not str

Moreover, the email package is pickier about encoding name synonyms than Python
and most other tools are: “latin-1” is detected as a quoted-printable MIME type, but

942 | Chapter 13: Client-Side Scripting