从模板到视图的Django变量 - 最佳实践

Question

I realize that using:

...
return render_to_response('mytemplate.html',
locals(), context_instance=RequestContext(request))

in views is not considered good code and something like:

...
return render_to_response('mytemplate.html', {
        'some_variable' : some_variable,
        'some_list': some_list,
}, context_instance=RequestContext(request)) 

is considered better for its legibility and explicitness. I was just curious how best to deal with variables which may or may not be returned. Should I explicitly set them in the views like this:

...
some_variable = None
some_variable = <some business logic>
return render_to_response('mytemplate.html', {
        'some_variable' : some_variable,
        'some_list': some_list,
}, context_instance=RequestContext(request)) 

which would result in more lengthy view code. Or should I check for existence of the variables before including them in the response?

Of course if I do nothing then I get:

local variable 'some_variable' referenced before assignment

Any suggestions welcomed.

Answer 1

A middle way is to use the context dictionary itself as a stack.

context = {}
if <condition>:
    context['cond1'] = 'foo'

if <condition2>:
    context['cond2'] = 'bar'

return render_to_response('template.html', context)

(Also note that since Django 1.3 you can use render(request, template, context) instead of the longwinded context_instance=RequestContext stuff.)

Answer 2

Either build your context conditionally, ie:

context = { 'some_list': some_list }

...

if <something>:
    context['some_variable'] = some_variable

...

return render_to_response('mytemplate.html', context, context_instance=RequestContext(request)    

Or use sensible defaults:

return render_to_response('mytemplate.html', {
    'some_variable' : some_variable or 'Default',
    'some_list': some_list,
}, context_instance=RequestContext(request))