Dotan Barak wrote:
On 25/12/2009 19:27, Gary Herron wrote:
Dotan Barak wrote:
Recover the exception, and examine the tuple of args or the message
string.
>>> try:
... eval("my_number < 10", {"__builtins__":None}, {})
... except NameError,e:
... print e.args
... print e.message
...
("name 'my_number' is not defined",)
name 'my_number' is not defined
First of all, thank - I really appreciate your response.
:)
I must admit that i don't like the idea of parsing a string (if
tomorrow the format of the message will change,
i will be in a deep trouble ...).
Is there is another way which doesn't involve string parsing?
Thanks
Dotan
OK. Try this: Executing your code attempts to lookup variables in a
local dictionary. You can rig up a local dictionary of your own
choosing -- in this case, I have it print the name of any variable that
is being looked up before actually doing the lookup. But at that
point, you have what you want, that is, the name as a string -- you can
do with it as you will -- record it, or print your nice error, or ...
You probably want to change my def of __getitem__ to attempt the lookup
first -- if that succeeds, return the value -- if it fails, then handle
the error.
Good luck,
Gary Herron
class D(dict):
def __getitem__(self, name):
print 'retrieving', name
return dict.__getitem__(self,name)
locals = D(b=123) # Defines b in a local dictionary
exec("a=2*b", locals) # Looks up b in locals
print locals['a'] # Returns the result (stored in 'a' in locals)
locals = D() # Does not define b in the local dictionary
exec("a=2*b", locals) # Fails to find b in locals
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