Marc Aymerich wrote:
> Dear all,
> I want to monkey patch a method that has lots of code so I want to avoid
> copying all the original method for changing just two lines. The thing is
> that I don't know how to do this kind of monkey patching.
>
> Consider the following code:
>
> class OringinalClass(object):
> def origina_method(self, *args, **kwargs):
> ...
> if some_condition(): # This condition should be changed
> raise SomeException
> ...
> if some_condition():
> ...
> #if some_condition(local_variable): # This condition should be
> #added
> # raise SomeException
> ...
>
>
> Is it possible to tell Python to run the original method without stopping
> when an exception is raised?
No.
> so I can catch them on a wrapper method and
> apply my conditional there.
>
> Any other idea on how to monkey patch those two conditionals ?
One of the cleanest alternatives is to factor out the condition in the
original class and then use a subclass:
class Original:
def method(self, *args, **kw):
self.check_condition(...)
...
def check_condition(self, ...):
if condition:
raise SomeException
class Sub(Original):
def check_condition(self, ...):
pass
If you insist on monkey-patching possible solutions depend on the actual
conditions. If some_condition() is a function, replace that function. If it
is actually an expression tweak the arguments. E. g:
>>> class Original:
... def method(self, x):
... if x < 0: raise ValueError
... print x * x
...
>>> Original().method(-2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 3, in method
ValueError
>>> class Int(int):
... def __lt__(self, other): return False # a blunt lie
...
>>> Original().method(Int(-2))
4
This tends to get complex quickly, so in the long run you will not be happy
with that approach...
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