Can't convert '__proxy__' object to str implicitly

When using the Bootstrap3 inline form field template using lazily translated field labels in the current dev branch, an error is raised on:

{% crispy_field field 'placeholder' field.label %}

The error comes down to:

File "..../django-crispy-forms/crispy_forms/templatetags/crispy_forms_field.py" in render
  134.                     widget.attrs[attribute_name] += " " + template.Variable(attribute).resolve(context)

Exception Type: TypeError at ...
Exception Value: Can't convert '__proxy__' object to str implicitly

This simple str call resolves the issue:

widget.attrs[attribute_name] += " " + str(template.Variable(attribute).resolve(context))

Using Django 1.7c2 on Python 3.4

[bayersglassey]

I’m not very familiar with the internals of Django’s lazy objects, but it seems to me like this could be fixed by defining __radd__ for the values returned by ugettext_lazy.

Minimal case of the error:

from django.utils.translation import ugettext_lazy as _
lazy_text = _("abc")
lazy_text + "123"  # works fine
"123" + lazy_text  # TypeError: Can't convert '__proxy__' object to str implicitly

…So if lazy_text.__radd__ was defined, I think this bug would be solved.

I did a quick test to make sure defining __radd__ lets us add to strings:

class A:
    def __radd__(self, x):
        return x + " A"
    def __add__(self, x):
        return "A " + x

a = A()
a+"123"  # "A 123"
"123"+a  # "123 A"   ...success!

[carltongibson]

@bayersglassey Nice example. This might be worth suggesting as a fix on Django.