Getting local dictionary for function scope only in Python

Question

I keep ending up at this situation where I want to use a dictionary very much like the one 'locals' gives back, but that only contains the variables in the limited scope of the function. Is there a way to do this in python?

A bit more about why I want to do this: I'm playing with Django and when I go to give my templates context, I am forced either to either manually make a dictionary (In violation with DRY principles) or pass in locals() which contains far more entries then are needed (wasteful). Is there perhaps something I'm missing with django which would alleviate the need of a python level solution?

To Clarify:

So, the case that I've hit repeatedly is where I have:

@render_to('my_template.html') 
def myview(request): 
    var1 = #blahblah 
    var2 = #... 
    # do stuff with vars 
    return {'var1': val1,'var2':val2} 

So instead of repeating those variables and naming conventions, I'll do:

@render_to('my_template.html') 
def myview(request): 
    var1 = #blahblah 
    var2 = #... 
    # do stuff with vars 
    return locals() 

Which I find cleaner, but I know its kind of sloppy since there are about 30 more entries in locals() then I actually need.

Answer 1

I'm not sure I agree that making a dictionary is a violation of DRY, but if you really don't want to repeat anything at all, you could just define a 'context' dictionary at the top of the view and use dictionary keys instead of variables throughout the view.

def my_view(request):
    context = {}
    context['items'] = Item.objects.all()
    context['anothervalue'] = context['items'][2].name
    return render_to_response('template.html', context)

Answer 2

How is passing a dictionary a violation of DRY? Django is all about DRY, so I doubt the standard behavior of it would directly violate it. In either case, however, I use a modified version of django-annoying to make the whole thing easier:

@render_to('my_template.html')
def myview(request):
    # figure stuff out...
    return {'var1':'val1','var2','val2'}

The render_to decorator takes care of the request context and all that good stuff. Works well.

If this doesn't help, I suggest rephrasing your question. Whatever you want to do messing around with locals() and such is rarely necessary especially in this kind of situation with Django.

Answer 3

You say you don't like using locals() because it is "wasteful". Wasteful of what? I believe the dictionary it returns already exists, it's just giving you a reference to it. And even if it has to create the dictionary, this is one of the most highly optimized operations in Python, so don't worry about it.

You should focus on the code structure that best expresses your intention, with the fewest possibilities for error. The waste you are worried about is nothing to worry about.

Answer 4

While I agree with many other respondents that passing either locals() or a fully specified dict {'var1':var1, 'var2': var2} is most likely OK, if you specifically want to "subset" a dict such as locals() that's far from hard either, e.g.:

loc = locals()
return dict((k,loc[k]) for k in 'var1 var2'.split())