Correction: Pascal inc(), not int()

Adrian Eyre a.eyre at optichrome.com
Mon Mar 20 15:30:10 CET 2000


On Fri, 17 Mar 2000, Michal Bozon wrote:

> Hi.
> 
> I want to have a function (of course in Python) equivalent to Pascal
> function inc(). (It increments an integer stored in argument by 1).
> 
> This should do folowwing:
> 
> >>> i = 10
> >>> inc(i)
> >>> i
> 11
> 
> eventually:
> 
> >>> i = 10
> >>> inc(i, 2)
> >>> i
> 12

Not possible without some extreme extension module hack, which is not
recommended. The problem is rebinding the new value into the calling
function's namespace. If you call a function like this...

>>> i = 1
>>> inc(i)

...you lose the name which is used to refer to that variable in that
namespace, so although you can get the value and increment it, you
can't rebind it. However... I could be wrong... :)

The closest I can get requires you to pass a stringified version of
the variable. This is still not recommended...

>>> import sys
>>> def inc(var, delta = 1):
... 	try:
... 		raise RuntimeError
... 	except RuntimeError:
... 		sys.exc_info()[2].tb_frame.f_back.f_locals[var] = \
...		sys.exc_info()[2].tb_frame.f_back.f_locals[var] + delta
... 
>>> i = 1
>>> inc("i")
>>> i
2
>>> inc("i", 40)
>>> i
42

-----------------------------------------------------------------
Adrian Eyre <a.eyre at optichrome.com> - http://www.optichrome.com 





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