Convert obejct string repr to actual object
Tor Erik Sønvisen
I've tried locating some code that can recreate an object from it's
string representation...
The object in question is really a dictionary containing other
dictionaries, lists, unicode strings, floats, ints, None, and
booleans.
I don't want to use eval, since I can't trust the source sending the
object.... I'm sure someone must have had the same need and created
code for it... Maybe Pypy has what I need??? Haven't looked though...
Regards,
Tor Erik
PS: The string repr is created by a server outside of my control...
Carsten Haese
> Hi,
>
> I've tried locating some code that can recreate an object from it's
> string representation...
> The object in question is really a dictionary containing other
> dictionaries, lists, unicode strings, floats, ints, None, and
> booleans.
>
> I don't want to use eval, since I can't trust the source sending the
> object.
You could still use eval, but run a separate algorithm first to make
sure the string is "legal." For example, you could whip up a simple
PyParsing grammar to restrict the set of allowable strings, or compile
the string into byte code and inspect the byte code to look for red
flags like LOAD_NAME (with a name other than None) and CALL_FUNCTION.
HTH,
--
Carsten Haese
http://informixdb.sourceforge.net
Chris Mellon
> Hi,
>
> I've tried locating some code that can recreate an object from it's
> string representation...
> The object in question is really a dictionary containing other
> dictionaries, lists, unicode strings, floats, ints, None, and
> booleans.
>
> I don't want to use eval, since I can't trust the source sending the
> code for it... Maybe Pypy has what I need??? Haven't looked though...
>
> Regards,
> Tor Erik
>
> PS: The string repr is created by a server outside of my control...
You'll need to write your own parser. PyParsing has an example that
can parse much of the Python syntax, you can probably extract the
object-literal parts of that and use it as a base for your
implementation.
Diez B. Roggisch
> Hi,
>
> I've tried locating some code that can recreate an object from it's
> string representation...
> The object in question is really a dictionary containing other
> dictionaries, lists, unicode strings, floats, ints, None, and
> booleans.
>
> I don't want to use eval, since I can't trust the source sending the
> object.... I'm sure someone must have had the same need and created
> code for it... Maybe Pypy has what I need??? Haven't looked though...
Try using simplejson.
Diez
Steven D'Aprano
wrote:
> I don't want to use eval, since I can't trust the source sending the
> object.... I'm sure someone must have had the same need and created code
> for it... Maybe Pypy has what I need??? Haven't looked though...
For the benefit of those who think they can make eval "safe", start here:
http://effbot.org/zone/librarybook-core-eval.htm
Here's a good solution:
http://effbot.org/zone/simple-iterator-parser.htm
--
Steven.
Michael Spencer
> Hi,
>
> I've tried locating some code that can recreate an object from it's
> string representation...
> The object in question is really a dictionary containing other
> dictionaries, lists, unicode strings, floats, ints, None, and
> booleans.
>
> object.... I'm sure someone must have had the same need and created
> code for it... Maybe Pypy has what I need??? Haven't looked though...
>
> Tor Erik
>
> PS: The string repr is created by a server outside of my control...
This recipe should get you most of what you need:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/364469
HTH
Michael
English, Mark
> Date: October 8th 2007
> I've tried locating some code that can recreate an object from
> it's string representation...
>>> class Foo(object): pass
>>> f = Foo()
>>> s = repr(f)
>>> s
'<__main__.Foo object at 0x007CBAB0>'
So how do I get f back from s ?
Obviously this is open to abuse. I just wondered if a mechanism existed short of writing
a C-extension which parses that string, casts the hex number to a PyObject *, INCREFs it,
and gives it back...
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Carsten Haese
> > From: Tor Erik Sønvisen
> > Date: October 8th 2007
> > I've tried locating some code that can recreate an object from
> > it's string representation...
> On a related note I've wondered about this:
> >>> class Foo(object): pass
> >>> f = Foo()
> >>> s = repr(f)
> >>> s
> '<__main__.Foo object at 0x007CBAB0>'
>
> So how do I get f back from s ?
> Obviously this is open to abuse. I just wondered if a mechanism existed short of writing
> a C-extension which parses that string, casts the hex number to a PyObject *, INCREFs it,
> and gives it back...
I can't help but wonder, do you often find yourself having to locate an
object from its hexadecimal address?
English, Mark
On 12 Oct, 18:14, Carsten Haese <cars...@uniqsys.com> wrote:
> On Fri, 2007-10-12 at 17:41 +0100, English, Mark wrote:
> > > From: Tor Erik Sønvisen
> > > Date: October 8th 2007
> > > I've tried locating some code that can recreate an object from
> > > it's string representation...
> > On a related note I've wondered about this:
> > >>> class Foo(object): pass
> > >>> f = Foo()
> > >>> s = repr(f)
> > >>> s
> > '<__main__.Foo object at 0x007CBAB0>'
> > So how do I get f back from s ?
>
> object from its hexadecimal address?
"For many types, this function makes an attempt to return a string that would yield an
object with the same value when passed to eval()"
I was just asking in case I was missing some mechanism which made new style class
instances fall under the heading of "many types" in this context.