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 jm.suresh@no.spam.gmail.com 01-11-2007 10:26 AM

dot operations

Hi,
Frequently I get to do like this:
a = (1, 2, 3, 4) # some dummy values
b = (4, 3, 2, 1)
import operator

I am finding the last line not very readable especially when I combine
couple of such operations into one line. Is it possible to overload
operators, so that, I can use .+ for element wise addition, as,
c = a .+ b

Similarly, I want to use .- , .*, ./ . Is it possible to do?

thanks.

-
Suresh

 robert 01-11-2007 10:41 AM

Re: dot operations

jm.suresh@no.spam.gmail.com wrote:
> Hi,
> Frequently I get to do like this:
> a = (1, 2, 3, 4) # some dummy values
> b = (4, 3, 2, 1)
> import operator
> c = map(operator.add, a, b)
>
> I am finding the last line not very readable especially when I combine
> couple of such operations into one line. Is it possible to overload
> operators, so that, I can use .+ for element wise addition, as,
> c = a .+ b
> which is much more readable.
>
> Similarly, I want to use .- , .*, ./ . Is it possible to do?

import numpy

You'll not even need dots

Re: dot operations

jm.suresh@no.spam.gmail.com wrote:
> Hi,
> Frequently I get to do like this:
> a = (1, 2, 3, 4) # some dummy values
> b = (4, 3, 2, 1)
> import operator
> c = map(operator.add, a, b)
>
> I am finding the last line not very readable especially when I combine
> couple of such operations into one line. Is it possible to overload
> operators, so that, I can use .+ for element wise addition, as,
> c = a .+ b
> which is much more readable.
>
> Similarly, I want to use .- , .*, ./ . Is it possible to do?
>
> thanks.
>
> -
> Suresh

List comprehensions?

>>> a = (1, 2, 3, 4)
>>> b = (4, 3, 2, 1)
>>> import operator
>>> c = map(operator.add, a, b)
>>> c

[5, 5, 5, 5]
>>> c1 = [a1+b1 for a1,b1 in zip(a,b)]
>>> c1

[5, 5, 5, 5]
>>>

 jm.suresh@no.spam.gmail.com 01-11-2007 02:06 PM

Re: dot operations

> jm.suresh@no.spam.gmail.com wrote:
> > Hi,
> > Frequently I get to do like this:
> > a = (1, 2, 3, 4) # some dummy values
> > b = (4, 3, 2, 1)
> > import operator
> > c = map(operator.add, a, b)
> >
> > I am finding the last line not very readable especially when I combine
> > couple of such operations into one line. Is it possible to overload
> > operators, so that, I can use .+ for element wise addition, as,
> > c = a .+ b
> > which is much more readable.
> >
> > Similarly, I want to use .- , .*, ./ . Is it possible to do?
> >
> > thanks.
> >
> > -
> > Suresh

>
> List comprehensions?
>
> >>> a = (1, 2, 3, 4)
> >>> b = (4, 3, 2, 1)
> >>> import operator
> >>> c = map(operator.add, a, b)
> >>> c

> [5, 5, 5, 5]
> >>> c1 = [a1+b1 for a1,b1 in zip(a,b)]
> >>> c1

> [5, 5, 5, 5]
> >>>

>

I just found this from :
http://aspn.activestate.com/ASPN/Coo.../Recipe/384122

class Infix(object):
def __init__(self, function):
self.function = function
def __ror__(self, other):
return Infix(lambda x, self=self, other=other:
self.function(other, x))
def __or__(self, other):
return self.function(other)
def __rlshift__(self, other):
return Infix(lambda x, self=self, other=other:
self.function(other, x))
def __rshift__(self, other):
return self.function(other)
def __call__(self, value1, value2):
return self.function(value1, value2)

import operator
dotplus = Infix(lambda x,y: map(operator.add, x, y))

a = range(4)
b = range(4)

c = a |dotplus| b

>

 Steven W. Orr 01-11-2007 04:21 PM

Re: dot operations

On Thursday, Jan 11th 2007 at 11:41 +0100, quoth robert:

=>jm.suresh@no.spam.gmail.com wrote:
=>> Hi,
=>> Frequently I get to do like this:
=>> a = (1, 2, 3, 4) # some dummy values
=>> b = (4, 3, 2, 1)
=>> import operator
=>> c = map(operator.add, a, b)
=>>
=>> I am finding the last line not very readable especially when I combine
=>> couple of such operations into one line. Is it possible to overload
=>> operators, so that, I can use .+ for element wise addition, as,
=>> c = a .+ b
=>> which is much more readable.
=>>
=>> Similarly, I want to use .- , .*, ./ . Is it possible to do?
=>
=>import numpy
=>
=>You'll not even need dots

I'm very new so my plea to be gentle is still on.

I just looked at the numpy package. Seems very cool, but for the life of
me I didn't understand the method by which python allows for creation of
infix operators. Can someone please explain or point me to a reference?

TIA

--
Time flies like the wind. Fruit flies like a banana. Stranger things have .0.
happened but none stranger than this. Does your driver's license say Organ ..0
Donor?Black holes are where God divided by zero. Listen to me! We are all- 000
individuals! What if this weren't a hypothetical question?
steveo at syslang.net

 Steven D'Aprano 01-11-2007 08:10 PM

Re: dot operations

On Thu, 11 Jan 2007 06:06:39 -0800, jm.suresh@no.spam.gmail.com wrote:

>> jm.suresh@no.spam.gmail.com wrote:
>> > Hi,
>> > Frequently I get to do like this:
>> > a = (1, 2, 3, 4) # some dummy values
>> > b = (4, 3, 2, 1)
>> > import operator
>> > c = map(operator.add, a, b)
>> >
>> > I am finding the last line not very readable especially when I combine
>> > couple of such operations into one line. Is it possible to overload
>> > operators, so that, I can use .+ for element wise addition, as,
>> > c = a .+ b
>> > which is much more readable.

[snip]

> I just found this from :
> http://aspn.activestate.com/ASPN/Coo.../Recipe/384122
>
> class Infix(object):

[snip code]

> c = a |dotplus| b

Personally, I find that to be the least readable of all the alternatives.
It is also slow, so slow that using it is (in my opinion) a pessimation
rather than an optimization.

Let me make the usual warnings about premature optimization being
the root of all evil, blah blah blah. Readability counts, and nobody cares
if you shave one hundredth of a millisecond off some code that your
program runs once. But, having said that, map is *fast*, especially with
the functions from operator.

>>> import timeit

.... "import operator; a = (1, 2, 3, 4); b = (4, 3, 2, 1)").timeit()
4.0072550773620605

It is even faster if you get rid of the dot lookup:

.... "a = (1, 2, 3, 4); b = (4, 3, 2, 1)").timeit()
3.6557090282440186

Using lambda can be much slower:

>>> timeit.Timer("map(lambda x,y: x+y, a, b)",

.... "a = (1, 2, 3, 4); b = (4, 3, 2, 1)").timeit()
6.1221940517425537

A list comprehension is in the middle, speed-wise:

>>> timeit.Timer("[x+y for x,y in zip(a,b)]",

.... "a = (1, 2, 3, 4); b = (4, 3, 2, 1)").timeit()
5.0318419933319092

But the Infix recipe is slower than a wet week:

>>> timeit.Timer("a|dotplus|b",

.... "a = (1, 2, 3, 4); b = (4, 3, 2, 1); "
.... "from __main__ import dotplus").timeit()
15.195909976959229

Speaking for myself, I find list comprehensions to be the most readable of
the alternatives and the most Pythonic.

--
Steven.

 Dan Bishop 01-12-2007 03:44 AM

Re: dot operations

On Jan 11, 10:21 am, "Steven W. Orr" <ste...@syslang.net> wrote:
> On Thursday, Jan 11th 2007 at 11:41 +0100, quoth robert:
>
> =>jm.sur...@no.spam.gmail.com wrote:=>> Hi,
> =>> Frequently I get to do like this:
> =>> a = (1, 2, 3, 4) # some dummy values
> =>> b = (4, 3, 2, 1)
> =>> import operator
> =>> c = map(operator.add, a, b)
> =>>
> =>> I am finding the last line not very readable especially when I combine
> =>> couple of such operations into one line. Is it possible to overload
> =>> operators, so that, I can use .+ for element wise addition, as,
> =>> c = a .+ b
> =>> which is much more readable.
> =>>
> =>> Similarly, I want to use .- , .*, ./ . Is it possible to do?
> =>
> =>import numpy
> =>
> =>You'll not even need dots
>
> I'm very new so my plea to be gentle is still on.
>
> I just looked at the numpy package. Seems very cool, but for the life of
> me I didn't understand the method by which python allows for creation of
> infix operators. Can someone please explain or point me to a reference?

Python doesn't allow the creation of new operators, but you can
overload the existing ones (except for "and" and "or"). This is done
by implementing the methods __add__, __sub__, __mul__, etc.

http://docs.python.org/ref/specialnames.html

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