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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: Dynamically determine base classes on instantiation
Date: Thu, 16 Aug 2012 12:29:21 -0400
Organization: > Bestiaria Support Staff <
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On Thu, 16 Aug 2012 14:52:30 +0200, Thomas Bach
<thbach@students.uni-mainz.de> declaimed the following in
gmane.comp.python.general:

> Thanks for the clarification on that one. So, here's the use-case: I'm
> querying the crunchbase API which returns JSON data and is rather
> poorly documented. I want to create a data model for the companies
> listed on Crunchbase in order to be able to put the queried data in a
> data-base. As I am too lazy to examine all the data by hand I thought
> I automatize this. I thought that it would be nice to be able to pass
> a function a parsed JSON object (AFAIK these are lists, dicts,
> strings, ints, floats, strs in Python) and it returns me the type of
> these objects. For the simple classes (str, int, float) this is quite
> trivial: F('foo') should return `str' and F(8) should return `int'.
>
	I'm not familiar with JSON structure, but off-hand I'd say the point
to determine the nature of the data is during the so-called parsing of
the JSON data itself, not after... Based upon http://www.json.org/ the
type of an item can basically be determined from the first character of
the "value":
{	dictionary (JSON "object")
[	list (JSON "array")
"	string
t/f/n		true/false/null
- or 0..9	number

	I'd be looking for some way to have the parser itself return a
structure of tuples of (type, parsedJSONitem)

	Of course, since the parse result (at least from my recent
experiment) is a Python structure, it isn't difficult to walk that
structure...

>>> import simplejson as j
>>> SAMPLE = '["foo", {"bar":["baz", null, 1.0, 2]}]'
>>> parse = j.loads(SAMPLE)
>>> parse
[u'foo', {u'bar': [u'baz', None, 1.0, 2]}]
>>> def typer(obj, level=0):
... 	otype = type(obj)
... 	print "\t" * level, otype
... 	if otype == type([]):
... 		for o in obj:
... 			typer(o, level+1)
... 	elif otype == type({}):
... 		for k,o in obj.items():
... 			print "\t" * level, "  ", k
... 			typer(o, level+1)
... 	else:
... 		print "\t" * level, "  ", obj
... 		
>>> print parse
[u'foo', {u'bar': [u'baz', None, 1.0, 2]}]
>>> typer(parse)
 <type 'list'>
	<type 'unicode'>
	   foo
	<type 'dict'>
	   bar
		<type 'list'>
			<type 'unicode'>
			   baz
			<type 'NoneType'>
			   None
			<type 'float'>
			   1.0
			<type 'int'>
			   2
>>> 

{Hmmm, forgot to print the type of "k" for dictionaries}.
 
> For a compound object like dict I would like it to return the data
> fields with their type. Hence, F({'foo': 8}) should return 
> {'foo': int}, and given that f = F({'foo': {'bar': 80}}) I would like
> f to equal to {'foo': dict}, with the option to query the type of
> 'foo' via f.foo, where the latter should equal to {'bar': int}. So
> far, this is not a complicated case. But, sometimes a data field on
> returned data set is simply None. Thus, I want to extract the types from
> another data set and merge the two.
> 

	"But, sometimes a data field on returned data set is simply None.
Thus, I want to extract the types from another data set and merge the
two." ??? A "data field" /value/ of None has the /type/ "<type
'NoneType'>", so I don't quite understand what you intend to merge? You
can't arbitrarily change the "type" without changing the "value".
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
        wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/