MySQLdb utf8_bin and django causes UnicodeDecodeError

[sam.vevang@…]

Issue:
I have a Model with a FileField. When I delete that instances of that model that have unicode characters in their filenames, I get a

'ascii' codec can't decode byte 0xc3 in position 18: ordinal not in
range(128) 

I finally traced the problem back to my database collation: utf8_bin. I chose utf8_bin so I could order the strings in a case-sensitive manner. FYI, MySQLdb does not return python unicode strings with a utf8_bin collation, it returns utf8 bytestrings. for a brief description of that issue see:
​http://code.djangoproject.com/ticket/8340#comment:4

The traceback from my exception reveals the exception being thrown in
"django/db/models/fields/files.py" in get_prep_value (line 248).
FileField is a subclass of Field, but implements the same backend
MySQL type (varchar) as a CharField. However it seems that FileField
and CharField have completely different implementations of
get_prep_db.

Here is CharField's implementation:

    def to_python(self, value):
        if isinstance(value, basestring) or value is None:
            return value
        return smart_unicode(value)

    def get_prep_value(self, value):
        return self.to_python(value)

Here is Filefield's:

    def get_prep_value(self, value):
        "Returns field's value prepared for saving into a database."
        # Need to convert File objects provided via a form to unicode for database insertion
        if value is None:
            return None
        return unicode(value)

My experimentations revealed that if I replace the FileField
implementation of get_prep_value with CharField's implementation, the exception
goes away. The issue is that the default encoding is ascii and so
unicode() called on a utf8 byte str blows up. The CharField
implementation simply checks if the value is an instance of basestring
and quietly passes it through.

[sam.vevang@…]

For clarity, I'll repost that code in code blocks:

Here is CharField's implementation:

    def to_python(self, value):
        if isinstance(value, basestring) or value is None:
            return value
        return smart_unicode(value)

    def get_prep_value(self, value):
        return self.to_python(value)

Here is Filefield's:

    def get_prep_value(self, value):
        "Returns field's value prepared for saving into a database."
        # Need to convert File objects provided via a form to unicode for database insertion
        if value is None:
            return None
        return unicode(value)