EmailMessage type checks should raise TypeError, not AssertionError

[Martín Blech]

If I run the following code:

email = EmailMessage(
    'Subject', 'Content',
    'from@example.com',
    'to@example.com')

print(email.message())

With the -O option, I get:

Traceback (most recent call last):
  File "x.py", line 6, in <module>
    'to@example.com')
  File "/home/berker/hacking/django/django/core/mail/message.py", line 227, in __init__
    assert not isinstance(to, six.string_types), '"to" argument must be a list or tuple'
AssertionError: "to" argument must be a list or tuple

But without it, it fails silently and produces a broken To header:

From nobody Wed Nov 26 18:30:08 2014
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Subject: Subject
From: from@example.com
To: t, o, @, e, x, a, m, p, l, e, ., c, o, m
Date: Wed, 26 Nov 2014 18:30:08 -0000
Message-ID: <20141126183008.1632.71698@rama>

Content

[Martín Blech]

​PR here

I'm still not sold on the error message, it says '"to" argument must be a list or tuple' but the actual check is isinstance(to, six.string_types). I think we should change one or the other.

[Tim Graham <timograham@…>]

In abf87333a163717308927ad1f230efe45d622c69:

Fixed #23924 -- Made EmailMessage raise TypeError for type checks