Is it possible to replace a Python function/method decorator at runtime?

As Miya mentioned, you can replace the decorator with another function any point before the interpreter gets to that function declaration. However, once the decorator is applied to the function, I don't think there is a way to dynamically replace the decorator with a different one. So for example:

@aDecorator
def myfunc1():
    pass

# Oops! I didn't want that decorator after all!

myfunc1 = bDecorator(myfunc1)

Won't work, because myfunc1 is no longer the function you originally defined; it has already been wrapped. The best approach here is to manually apply the decorators, oldskool-style, i.e:

def myfunc1():
    pass

myfunc2 = aDecorator(myfunc1)
myfunc3 = bDecorator(myfunc1)

Edit: Or, to be a little clearer,

def _tempFunc():
    pass

myfunc1 = aDecorator(_tempFunc)
myfunc1()
myfunc1 = bDecorator(_tempFunc)
myfunc1()

I don't know if there's a way to "replace" a decorator once it has been applied, but I guess that probably there's not, because the function has already been changed.

You might, anyway, apply a decorator at runtime based on some condition:

#!/usr/bin/env python

class PrintCallInfo:
    def __init__(self,f):
        self.f = f
    def __call__(self,*args,**kwargs):
        print "-->",self.f.__name__,args,kwargs
        r = self.f(*args,**kwargs)
        print "<--",self.f.__name__,"returned: ",r
        return r

# the condition to modify the function...
some_condition=True

def my_decorator(f):
    if (some_condition): # modify the function
        return PrintCallInfo(f)
    else: # leave it as it is
        return f

@my_decorator
def foo():
    print "foo"

@my_decorator
def bar(s):
    print "hello",s
    return s

@my_decorator
def foobar(x=1,y=2):
    print x,y
    return x + y

foo()
bar("world")
foobar(y=5)