Re: A question on python performance.
Joe Goldthwaite wrote: I didn't know about the getattr function. I tried to search for that type of function but not knowing how to word the search request, I couldn't find it. You should really read through chapter 2 (Built-in Objects) of the library reference. All that stuff is core Python functionality that you should be aware of. Reading chapter 3 (Built-in Types) is also a really good idea. A lot of the rest is good too, but there is really no excuse for not knowing the contents of those chapters. ;) It's just a few pages, and very useful to know. Read them now! -- http://mail.python.org/mailman/listinfo/python-list
Re: A question on python performance.
Joe Goldthwaite a écrit : (snip) I guess I still think of decorators as the people who got the gym ready for the prom. I've tried getting up to speed on decorators but I haven't had much success. The @decorator syntax is just syntactic sugar for a common use of higher order functions. So to understand decorators, you first need understand the concepts of higher order functions and closures. Both are documented in many places on the web. Bruno Desthuilliers wrote: IOW, direct access to obj.__class__.__dict__ bypasses both inheritence and per-instance overriding. Thanks for your response also Bruno. I don't understand the code you posted well enough yet to even ask a useful question. There are a number of things I haven't seen before. It's very 101 python code, apart from this line : c2.dothis = dothat.__get__(c2, type(c2)) which is a way to dynamically attach a function as method to an instance, directly invoking the descriptor protocol (it's documented on python.org) FWIW, it's most often done using the 'new' module, and possibly less confusing: import new c2.dothis = new.instancemethod(dothat, c2, type(c2)) Now I really feel like a newbie! My fault - this example wasn't that necessary, the main point was wrt/ direct access to instance.__class__.__dict__ bypassing normal attribute lookup rules so inherited attributes are not resolved... I'm working on it though so I may have some questions later. You're welcome. -- http://mail.python.org/mailman/listinfo/python-list
RE: A question on python performance.
[EMAIL PROTECTED] wrote: Makes perfect sense to me! Think about it: method 1: looks up the method directly from the object (fastest) method 2: looks up __class__, then looks up __dict__, then gets the element from __dict__ method 3: looks up caller, looks up __class__, looks up __dict__, gets element from __dict__ To get the element directly from the object (method 1), Python has to internally check __class__.__dict__[element], which shows why method 1 and method 2 are nearly the same speed. The last version has to look up caller in addition to the process described by method 2. The best way to do what you are doing: getattr(self, param)(self, *args) I didn't know about the getattr function. I tried to search for that type of function but not knowing how to word the search request, I couldn't find it. That's a lot cleaner way of doing what I was trying to do. I benchmarked it and it's so close in speed to the hard-coded method as to be identical. Paul Hankin wrote: You're calling a function (getValue) that just calls a method of trend (caller), that just calls another method of trend (Ptd or Qtd or ...). You can skip all these steps, and just call the method yourself: the code that calls getValue(trend, param, per) replace with trend.something(per) if you're calling getValue with a static value for param, or getattr(trend, param)(per) if param is dynamic. You're right, it makes sense. Thanks for also pointing out the getattr function. Eric Jones wrote: What you're describing is a case of mulitple dispatch. See http:// www.artima.com/weblogs/viewpost.jsp?thread=101605 for a short description and (as short) example by Guido. You can probably fill that out and adapt it to your needs. Alternatively, you could look into the multimethods module in the Gnosis Utilities package: http:// pypi.python.org/pypi/Gnosis_Utils/1.2.1-a Thanks Eric. I read that article on multi-methods but I can't say I really understand it. I guess I still think of decorators as the people who got the gym ready for the prom. I've tried getting up to speed on decorators but I haven't had much success. Like I mentioned previously, with Python, I still feel like a newbie. Bruno Desthuilliers wrote: IOW, direct access to obj.__class__.__dict__ bypasses both inheritence and per-instance overriding. Thanks for your response also Bruno. I don't understand the code you posted well enough yet to even ask a useful question. There are a number of things I haven't seen before. Now I really feel like a newbie! I'm working on it though so I may have some questions later. Thanks again for everyone's input. I really appreciate it. -- http://mail.python.org/mailman/listinfo/python-list
A question on python performance.
Hi everyone,
I'm a developer who's been using python for a couple of years. I wrote a
fairly large application using it but I was learning the language at the
same time so it most of the code kind of sucks.
I've learned a lot since then and I've been going through my code trying to
organize it better and make better use of Python's features. I'm still not
an expert by any definition but I'm slowly getting better.
I've been working on a trend class that takes twelve monthly numbers and
returns a period to date, quarter to date, year to date and quarterly year
to date numbers for a specific period. This worked but I ended up with a lot
of code like this;
def getValue(trend, param, per):
if param == 'Ptd':
return trend.Ptd(per)
elif param == 'Qtd':
return trend.Qtd(per)
elif param == 'Ytd':
return trend.Ytd(per)
elif param == 'YtdQ':
return trend.YtdQ(per)
The code gets kind of wordy so I started trying to figure out how to call
them dynamically since the param type is the same as the method the
retrieves it. I came up with this;
def getValue(trend, param, per):
return trend.__class__.__dict__[param](trend, per)
That worked but it seems like the above line would have to do lots more
object look ups at runtime so I didn't think it would be very efficient. I
thought maybe I could add a caller method to the trend class and I came up
with this;
class trend:
...
...
...
def caller(self, param, *args):
return self.__class__.__dict__[param](self, *args)
This simplified the getValue function to this;
def getValue(trend, param, per):
return trend.caller(param, per)
Out of curiosity, I thought I'd do some benchmarking and see which one
performs the best. I executed three multiple times;
loop one. Time=11.71 seconds;
trend.Ptd(per)
trend.Qtd(per)
trend.Ytd(per)
trend.YtdQ(per)
loop two. 12.107 seconds;
trend.__class__.__dict__['Ptd'](trend, per)
trend.__class__.__dict__['Qtd'](trend, per)
trend.__class__.__dict__['Ytd'](trend, per)
trend.__class__.__dict__['YtdQ'](trend, per)
loop three. 17.085 seconds;
trend.caller('Ptd', per)
trend.caller('Qtd', per)
trend.caller('Ytd', per)
trend.caller('YtdQ', per)
The first surprise was how close the first and second loops were. I would
have thought the first loop would be much faster. The second surprise was
how much slower the third loop was. I know it has an extra call in there
but other than that, it's doing basically the same thing as loop two. Is
there that much overhead in making a class method call?
Can anyone explain the differences?
--
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Re: A question on python performance.
On Sep 26, 2:26 pm, Joe Goldthwaite [EMAIL PROTECTED] wrote:
Hi everyone,
I'm a developer who's been using python for a couple of years. I wrote a
fairly large application using it but I was learning the language at the
same time so it most of the code kind of sucks.
I've learned a lot since then and I've been going through my code trying to
organize it better and make better use of Python's features. I'm still not
an expert by any definition but I'm slowly getting better.
I've been working on a trend class that takes twelve monthly numbers and
returns a period to date, quarter to date, year to date and quarterly year
to date numbers for a specific period. This worked but I ended up with a lot
of code like this;
def getValue(trend, param, per):
if param == 'Ptd':
return trend.Ptd(per)
elif param == 'Qtd':
return trend.Qtd(per)
elif param == 'Ytd':
return trend.Ytd(per)
elif param == 'YtdQ':
return trend.YtdQ(per)
The code gets kind of wordy so I started trying to figure out how to call
them dynamically since the param type is the same as the method the
retrieves it. I came up with this;
def getValue(trend, param, per):
return trend.__class__.__dict__[param](trend, per)
That worked but it seems like the above line would have to do lots more
object look ups at runtime so I didn't think it would be very efficient. I
thought maybe I could add a caller method to the trend class and I came up
with this;
class trend:
...
...
...
def caller(self, param, *args):
return self.__class__.__dict__[param](self, *args)
This simplified the getValue function to this;
def getValue(trend, param, per):
return trend.caller(param, per)
Out of curiosity, I thought I'd do some benchmarking and see which one
performs the best. I executed three multiple times;
loop one. Time=11.71 seconds;
trend.Ptd(per)
trend.Qtd(per)
trend.Ytd(per)
trend.YtdQ(per)
loop two. 12.107 seconds;
trend.__class__.__dict__['Ptd'](trend, per)
trend.__class__.__dict__['Qtd'](trend, per)
trend.__class__.__dict__['Ytd'](trend, per)
trend.__class__.__dict__['YtdQ'](trend, per)
loop three. 17.085 seconds;
trend.caller('Ptd', per)
trend.caller('Qtd', per)
trend.caller('Ytd', per)
trend.caller('YtdQ', per)
The first surprise was how close the first and second loops were. I would
have thought the first loop would be much faster. The second surprise was
how much slower the third loop was. I know it has an extra call in there
but other than that, it's doing basically the same thing as loop two. Is
there that much overhead in making a class method call?
Can anyone explain the differences?
Makes perfect sense to me! Think about it:
method 1: looks up the method directly from the object (fastest)
method 2: looks up __class__, then looks up __dict__, then gets the
element from __dict__
method 3: looks up caller, looks up __class__, looks up __dict__, gets
element from __dict__
To get the element directly from the object (method 1), Python has to
internally check __class__.__dict__[element], which shows why method 1
and method 2 are nearly the same speed. The last version has to look
up caller in addition to the process described by method 2.
The best way to do what you are doing:
getattr(self, param)(self, *args)
--
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Re: A question on python performance.
On Sep 26, 2007, at 1:26 PM, Joe Goldthwaite wrote: Hi everyone, I'm a developer who's been using python for a couple of years. I wrote a fairly large application using it but I was learning the language at the same time so it most of the code kind of sucks. I've learned a lot since then and I've been going through my code trying to organize it better and make better use of Python's features. I'm still not an expert by any definition but I'm slowly getting better. I've been working on a trend class that takes twelve monthly numbers and returns a period to date, quarter to date, year to date and quarterly year to date numbers for a specific period. This worked but I ended up with a lot of code like this; def getValue(trend, param, per): if param == 'Ptd': return trend.Ptd(per) elif param == 'Qtd': return trend.Qtd(per) elif param == 'Ytd': return trend.Ytd(per) elif param == 'YtdQ': return trend.YtdQ(per) The code gets kind of wordy so I started trying to figure out how to call them dynamically since the param type is the same as the method the retrieves it. I came up with this; def getValue(trend, param, per): return trend.__class__.__dict__[param](trend, per) That worked but it seems like the above line would have to do lots more object look ups at runtime so I didn't think it would be very efficient. I thought maybe I could add a caller method to the trend class and I came up with this; class trend: ... ... ... def caller(self, param, *args): return self.__class__.__dict__[param](self, *args) This simplified the getValue function to this; def getValue(trend, param, per): return trend.caller(param, per) What you're describing is a case of mulitple dispatch. See http:// www.artima.com/weblogs/viewpost.jsp?thread=101605 for a short description and (as short) example by Guido. You can probably fill that out and adapt it to your needs. Alternatively, you could look into the multimethods module in the Gnosis Utilities package: http:// pypi.python.org/pypi/Gnosis_Utils/1.2.1-a Erik Jones Software Developer | Emma® [EMAIL PROTECTED] 800.595.4401 or 615.292.5888 615.292.0777 (fax) Emma helps organizations everywhere communicate market in style. Visit us online at http://www.myemma.com -- http://mail.python.org/mailman/listinfo/python-list
Re: A question on python performance.
On Sep 26, 7:26 pm, Joe Goldthwaite [EMAIL PROTECTED] wrote: The code gets kind of wordy so I started trying to figure out how to call them dynamically since the param type is the same as the method the retrieves it. I came up with this; def getValue(trend, param, per): return trend.__class__.__dict__[param](trend, per) That worked but it seems like the above line would have to do lots more object look ups at runtime so I didn't think it would be very efficient. I thought maybe I could add a caller method to the trend class and I came up with this; class trend: ... ... ... def caller(self, param, *args): return self.__class__.__dict__[param](self, *args) This simplified the getValue function to this; def getValue(trend, param, per): return trend.caller(param, per) You're calling a function (getValue) that just calls a method of trend (caller), that just calls another method of trend (Ptd or Qtd or ...). You can skip all these steps, and just call the method yourself: the code that calls getValue(trend, param, per) replace with trend.something(per) if you're calling getValue with a static value for param, or getattr(trend, param)(per) if param is dynamic. -- Paul Hankin -- http://mail.python.org/mailman/listinfo/python-list
Re: A question on python performance.
Joe Goldthwaite a écrit :
Hi everyone,
I'm a developer who's been using python for a couple of years. I wrote a
fairly large application using it but I was learning the language at the
same time so it most of the code kind of sucks.
I've learned a lot since then and I've been going through my code trying to
organize it better and make better use of Python's features. I'm still not
an expert by any definition but I'm slowly getting better.
I've been working on a trend class that takes twelve monthly numbers and
returns a period to date, quarter to date, year to date and quarterly year
to date numbers for a specific period. This worked but I ended up with a lot
of code like this;
def getValue(trend, param, per):
if param == 'Ptd':
return trend.Ptd(per)
elif param == 'Qtd':
return trend.Qtd(per)
elif param == 'Ytd':
return trend.Ytd(per)
elif param == 'YtdQ':
return trend.YtdQ(per)
The first obvious simplification is to replace this with:
def getValue(trend, param, per):
meth = getattr(trend, param)
return meth(per)
The main difference is that it will raise (instead of returning None) if
param is not the name of a method of trend.
The second simplification is to either get rid of getValue() (which is
mostly useless).
The code gets kind of wordy
indeed
so I started trying to figure out how to call
them dynamically since the param type is the same as the method the
retrieves it. I came up with this;
def getValue(trend, param, per):
return trend.__class__.__dict__[param](trend, per)
Note that this is not strictly equivalent:
class Parent(object):
def __init__(self, name):
self.name = name
def __repr__(self):
return %s %s % (self.__class__.__name__, self.name)
def dothis(self):
return parent.dothis %s % self
class Child(Parent):
def dothis(self):
return Child.dothis %s % self
class OtherChild(Parent): pass
def dothat(obj):
return dothat %s % obj
p = Parent('p')
c1 = Child('c1')
c2 = Child('c2')
c2.dothis = dothat.__get__(c2, type(c2))
o1 = OtherChild('o1');
o2 = OtherChild('o2');
o2.dothis = dothat.__get__(o2, type(o2))
for obj in p, c1, c2, o1, o2:
print obj : %s % obj
print direct call :
print obj.dothis()
print via obj.__class__.__dict__ :
try:
print obj.__class__.__dict__[dothis](obj)
except KeyError, e:
print oops - key error: %s % e
print
=
obj : Parent p
direct call :
parent.dothis Parent p
via obj.__class__.__dict__ :
parent.dothis Parent p
obj : Child c1
direct call :
Child.dothis Child c1
via obj.__class__.__dict__ :
Child.dothis Child c1
obj : Child c2
direct call :
dothat Child c2
via obj.__class__.__dict__ :
Child.dothis Child c2
obj : OtherChild o1
direct call :
parent.dothis OtherChild o1
via obj.__class__.__dict__ :
oops - key error: 'dothis'
obj : OtherChild o2
direct call :
dothat OtherChild o2
via obj.__class__.__dict__ :
oops - key error: 'dothis'
IOW, direct access to obj.__class__.__dict__ bypasses both inheritence
and per-instance overriding.
That worked but it seems like the above line would have to do lots more
object look ups at runtime so I didn't think it would be very efficient. I
thought maybe I could add a caller method to the trend class and I came up
with this;
class trend:
...
...
...
def caller(self, param, *args):
return self.__class__.__dict__[param](self, *args)
This simplified the getValue function to this;
def getValue(trend, param, per):
return trend.caller(param, per)
Err... It actually means *more* lookup and function calls - and still
fails to behave correctly wrt/ polymorphic dispatch.
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