Python : convert unicode string to raw object/text

Question

I've got a set of key, value pairs dictionary in my Django application. The value in the dictionary is a string type.

{u'question': u'forms.CharField(max_length=512)'}

I need to convert this "value" string to an actual object, and get something like this.

properties = {
    'question' : forms.CharField(max_lenth=512)
    }

Notice that values in the second dictionary are actual Django form fields and NOT strings. I need to do this manipulation to create dynamic forms. The second dictionary is to be passed to "type" built-in function. Sample code can be found on this page. http://dougalmatthews.com/articles/2009/dec/16/nicer-dynamic-forms-django/ .

@ignacio : Sure. I'm just learning stuff here. The only constraint is that I need to create forms on the fly/dynamically. — Neo
– Neo, Commented Mar 14, 2011 at 8:53

Ignacio Vazquez-Abrams · Accepted Answer · 2011-03-14 09:10:32Z

3

If you modify your representation a bit:

fields = {u'question': u'{"field": "django.forms.CharField", "params": {"max_length": 512}}'}

then you can use the following:

from django.utils import importlib, simplejson

def get_field(fname):
  module, name = fname.rsplit('.', 1)
  return getattr(importlib.import_module(module), name)

print dict((k.encode('ascii', 'ignore'), get_field(v['field'])(**v['params']))
  for k, v in ((k, simplejson.loads(v)) for k, v in fields.iteritems()))

answered Mar 14, 2011 at 9:10

Ignacio Vazquez-Abrams

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Comments

Don · Accepted Answer · 2011-03-14 09:04:25Z

1

Following your code, I suggest to separate field name from field attrs:

my_fields = {u'question': {'name': 'CharField', 'attrs': {'max_length': 512} }}

and then something like:

properties = {}
for field_name, field_def in my_fields.items():
    properties[field_name] = getattr(forms, field_def['name'])(**field_def['attrs'])

answered Mar 14, 2011 at 9:04

Don

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Marcelo Cantos · Accepted Answer · 2011-03-14 09:14:33Z

0

EDIT: Based on clarifying comments by the OP, this isn't an appropriate solution.

I don't know the constraints you are under, but perhaps the following representation will work better:

{u'question': lambda: forms.CharField(max_length=512)}

You can then "realise" the fields thus:

dict((k, v()) for (k, v) in props.iteritems())

edited Mar 14, 2011 at 9:14

answered Mar 14, 2011 at 9:03

Marcelo Cantos

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5 Comments

Ignacio Vazquez-Abrams Over a year ago

That's not really a representation though.

Marcelo Cantos Over a year ago

@Ignacio: "Representation" is an extremely broad term that covers statements like, "A lambda function is a representation of a computation". Perhaps you had a more narrowly-defined meaning in mind.

Neo Over a year ago

The question I've posted is a sort of simplification. Actually, I have a database model, that stores Field and corresponding django form field. Ex "Char" -> "form.Charfield(max_lenght=512)" etc. So depending on user input, I retrieve a corresponding string for each field type. Should I store something other than string my model database?

Marcelo Cantos Over a year ago

@Neo: In that case, what you are doing is probably the simplest solution. You can convert any string representing a Python value back to that value using Python's eval function.

Neo Over a year ago

Using eval gives me the following error 'module' object has no attribute 'CharField'. Maybe I should statically declare the objects types in the file as a dictionary, rather than the database.

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