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Why do Python's frameworks return dictionaries from controllers?

Answer 1

+4 A:

The main advantage is that this is the only way in python to return a) more than a single value and b) give that value a name. Other options would be to use a class (extra code), return a tuple (no names, so you'd have to use indexes to access the values) or allow to return only a single value which would probably mean that everyone would return a dictionary since that's the most simple solution.

It also allows to wrap several methods and join/merge their results. Lastly, it allows to return different sets of value/name pairs for each call easily, for example, omit optional values or return additional hints.

Aaron Digulla 2009-03-11 11:13:09

In Python 2.6+ `collections.namedtuple` allows both to return multiple values and to give names to these values.

J.F. Sebastian 2009-03-11 11:27:55

So, why in rails the @variable is chosen to export variables to views? Why the same approach is not followed by other python frameworks?

Jon Romero 2009-03-11 11:53:13

I don't know about rails but maybe they try to prevent to leak internal information (which is why most frameworks don't use local()). As for other frameworks: I know that TurboGears and web2py use this approach. From my point of view, that's "all". Dunno about Django.

Aaron Digulla 2009-03-11 12:47:22

Or maybe the Rails syntax would make this approach "ugly".

Aaron Digulla 2009-03-11 12:48:31

Answer 2

A:

The nice thing is that a template engine like Jinja2 treats an object and a dict similarly, so if:

d = {'color': 'red'}
o = Color(red)

then these all work in the template syntax:

d.color d['color'] o.color o['color']

Ali A 2009-03-11 11:19:50

Answer 3

+3 A:

You can use local variables if you'd like:

def hello():
    var1 = "whatever you like"
    var2 = "another value"
    return locals() # or vars()

hello.html:

<html><body>
 <p>var1 {{=var1}}</p>
 <p>var2 {{=var2}}</p>
</body></html>

from PHP to web2py:

In web2py an HTTP request for "/app/c/f" is mapped into a call to the function f() in file (controller) c.py in the application "app". The file c.py is written in Python. The output of the function f() can be a string (in this case it is returned), or a set of variables (implemented as a python dictionary). In the latter case the variables are rendered into HTML by a file c/f.html, called a view.

J.F. Sebastian 2009-03-11 11:37:08

Not really a recommended approach, though, as it's an easy way to end up passing data to your templates that you never intended to pass.

Carl Meyer 2009-03-11 14:28:33

@Carl Meyer: I agree. Explicit dictionary is better.

J.F. Sebastian 2009-03-11 14:32:03

for small functions like that I would just return locals() to same space

Plumo 2009-09-01 06:09:13

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Why do Python's frameworks return dictionaries from controllers?

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