pyrex functions to replace a method (Re: replace a method in class:how?)

[Brian Blais]

Thanks for all who replied to this question about replacing a method. I feel a
little sheepish for not having caught that I have to replace it in the class, not the
instance, but I have found a very similar problem trying to replace a method using a
function defined in pyrex. I post all of the code below, but there are several files.

The main code is:

import module_py # import a function from a python module
import module_pyrex # import a function from a pyrex extension module

class This(object):

def update1(self,val):
print val

def update2(self,val):
print "2",val

def update3(self,val):
print "3",val

def local_update(obj,val):

print "local",val


This.update1=local_update # replace the method from a local function
This.update2=module_py.python_update # replace the method from a python module
This.update3=module_pyrex.pyrex_update # replace the method from a pyrex module

t=This()

t.update1('local') # works fine
t.update2('python') # works fine
t.update3('pyrex') # gives a typeerror function takes exactly 2 arguments (1 given)
#---------------------------------------------------------------------------------

#module_py.py

def python_update(self,val):
print "python module",val
#---------------------------------------------------------------------------------

#module_pyrex.pyx

def pyrex_update(self,val):
print "pyrex module",val

#---------------------------------------------------------------------------------


any ideas why the pyrex function fails?


thanks,


bb

 

[Bruno Desthuilliers]

Thanks for all who replied to this question about replacing a method. I
feel a little sheepish for not having caught that I have to replace it
in the class, not the instance,

But you *can* replace it on a per-instance basis. It's easy, perfectly
legal, and can be very convenient.

<rant>
I'm very sorry that some poster here try to forcefit Javaish restricted
OO conception into Python. Free your mind, burn your books, and take
full advantage of Python's powerfull object model.

but I have found a very similar problem
trying to replace a method using a function defined in pyrex. I post
all of the code below, but there are several files.

The main code is:

import module_py # import a function from a python module
import module_pyrex # import a function from a pyrex extension module

class This(object):

def update1(self,val):
print val

def update2(self,val):
print "2",val

def update3(self,val):
print "3",val

def local_update(obj,val):

print "local",val


This.update1=local_update # replace the method from a local function
This.update2=module_py.python_update # replace the method from a python
module
This.update3=module_pyrex.pyrex_update # replace the method from a
pyrex module

Note that - from a purely technical POV - you don't need to define the
updateXXX methods in This. You can add methods directly - in fact,
defining a function in a class statement will end up doing the same
thing as binding it to the class objet outside the class statement.

t=This()

t.update1('local') # works fine
t.update2('python') # works fine
t.update3('pyrex') # gives a typeerror function takes exactly 2
arguments (1 given)
(snip)

any ideas why the pyrex function fails?

I don't have much knowledge wrt/ pyrex, but I guess that pyrex functions
don't implement the descriptor protocol as pure Python functions do, so
the instance object is not passed to the function at calltime.