On 4 November 2012 13:32, Roy Smith <r...@panix.com> wrote: > Environment: > Python-2.7.3 > Ubuntu Precise > mongoengine 0.6.20 > > I have a class which includes a __unicode__() method: > > class User(mongoengine.Document): > def __unicode__(self): > return self.username > > If I create an instance of this class by calling the constructor > directly, self.username is None. When I pass that to unicode(), it > blows up. However, calling __unicode__() directly, works as expected: > > >>> u = User() > >>> print u.username > None > > >>> print u.__unicode__() > None > > >>> print unicode(u) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: coercing to Unicode: need string or buffer, NoneType found > > What's going on here? I thought > (http://docs.python.org/2/library/functions.html#unicode) the latter two > calls should be identical, but obviously they're not.
>>> class Foo: ... def __unicode__(self): return "Bar" # NOT Unicode ... >>> Foo().__unicode__() 'Bar' >>> unicode(Foo()) u'Bar' unicode(x) calls x.__unicode__() *and then* coerces the result to Unicode. None cannot be coerced to Unicode.
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