LX wrote:
On Mar 30, 2:41 pm, MRAB <pyt...@mrabarnett.plus.com> wrote:
LX wrote:
On Mar 29, 6:34 pm, MRAB <pyt...@mrabarnett.plus.com> wrote:
LX wrote:
Hi all, I have a question about decorators. I would like to use them
for argument checking, and pre/post conditions. However, I don't want
the additional overhead when I run in non-debug mode. I could do
something like this, using a simple trace example.
@decorator
def pass_decorator(f, *args, **kw): # what about the slow-down that
incurs when using pass_decorator?
return f(*args, **kw)
@decorator
def trace_decorator(f, *args, **kw):
print "calling %s with args %s, %s" % (f.func_name, args, kw)
return f(*args, **kw)
trace_enable_flag = False #__debug__
trace = trace_decorator if trace_enable_flag else pass_decorator
Trouble is, there is still an additional encapsulating function call.
Is there any way to eliminate the extra function call altogether?
Thanks in advance!
I think you have misunderstood certain details about decorators.
This code with adecorator:
@decorator
def hello():
print "hello world"
basically does this:
def hello():
print "hello world"
hello =decorator(hello)
so your non-decoratorjust needs to return the function it was passed:
def pass_decorator(func):
return func
and your tracedecoratorwould be something like this:
def trace_decorator(func):
def show(*args, **kwargs):
print "calling %s with args %s, %s" % (func.func_name,
args, kwargs)
result = func(*args, **kwargs)
print "returning %s from %s" % (result, func.func_name)
return result
return show
Sure, but during runtime, pass_decorator will still be called, even
though it doesn't do anything. I am wondering if I can disable this
additional function call at non-debug runtime. In other words, I want
the calling stack to contain nodecoratorat all, not even
pass_decorator.
I should mention that, in my code, the symbol "decorator" is imported
from Michele Simionato'sdecorator.py file.
pass_decorator will be called when the decorated function is _defined_,
but not when the decorated function is _called_.
Why is it then that during runtime, with a breakpoint in some
arbitrary main() in main.py, I get something similar to the following
call stack:
main.py, line xxx, in <module>
main()
<string>, line 2, in main
decorator.py, line 261, in pass_decorator
return f(*args, **kw)
main.py, line yyy, in main()
* breakpoint line here *
It looks to me the call stack still includes the additional level of
the decorator... what am I missing? Thank you for your time.
Are you still defining your decorators in the same way as in your
original post?
A decorator shouldn't call the function it's decorating.
My version of pass_decorator just returns the function it's decorating,
not call it, and my version of trace_decorator returns a locally-defined
function which will call the decorated function.
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