functions which take functions

Kiuhnm

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Apr 9, 2012, 2:57:00 PM4/9/12

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Do you have some real or realistic (but easy and self-contained)
examples when you had to define a (multi-statement) function and pass it
to another function?
Thank you.

Kiuhnm

Ulrich Eckhardt

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Apr 10, 2012, 8:29:03 AM4/10/12

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Am 09.04.2012 20:57, schrieb Kiuhnm:
> Do you have some real or realistic (but easy and self-contained)
> examples when you had to define a (multi-statement) function and pass it
> to another function?

Take a look at decorators, they not only take non-trivial functions but
also return them. That said, I wonder what your intention behind this
question is...

:)

Uli

Kiuhnm

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Apr 10, 2012, 9:36:26 AM4/10/12

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That won't do. A good example is when you pass a function to re.sub, for
instance.

Kiuhnm

Eelco

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Apr 10, 2012, 5:43:08 PM4/10/12

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Wont do for what? Seems like a perfect example of function-passing to
me.

If you have such a precise notion of what it is you are looking for,
why even ask?

Kiuhnm

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Apr 11, 2012, 6:55:26 AM4/11/12

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On 4/10/2012 23:43, Eelco wrote:
> On Apr 10, 3:36 am, Kiuhnm<kiuhnm03.4t.yahoo.it> wrote:
>> On 4/10/2012 14:29, Ulrich Eckhardt wrote:
>>
>>> Am 09.04.2012 20:57, schrieb Kiuhnm:
>>>> Do you have some real or realistic (but easy and self-contained)
>>>> examples when you had to define a (multi-statement) function and pass it
>>>> to another function?
>>
>>> Take a look at decorators, they not only take non-trivial functions but
>>> also return them. That said, I wonder what your intention behind this
>>> question is...
>>
>>> :)
>>
>> That won't do. A good example is when you pass a function to re.sub, for
>> instance.
>>
>> Kiuhnm
>
> Wont do for what? Seems like a perfect example of function-passing to
> me.

That's more an example of function transformation.

> If you have such a precise notion of what it is you are looking for,
> why even ask?

As I said, I need real-life examples. Enough with prime numbers and
recursive qsort...

Kiuhnm

Antti J Ylikoski

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Apr 11, 2012, 10:01:38 AM4/11/12

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A function to numerically integrate another function comes as follows:

------------------------------------------------------

# Adaptive Simpson's integral.
#
# AJY 03-28-2012 from the Wikipedia.

import math

def simpsonsRule(f,a,b):
c = (a+b) / 2.0
h3 = abs(b-a) / 6.0
return h3*(f(a) + 4.0*f(c) + f(b))

def recursiveASR(f,a,b,eps,whole):
"Recursive implementation of adaptive Simpson's rule."
c = (a+b) / 2.0
left = simpsonsRule(f,a,c)
right = simpsonsRule(f,c,b)
if abs(left + right - whole) <= 15*eps:
return left + right + (left + right - whole)/15.0
return recursiveASR(f,a,c,eps/2.0,left) + \
recursiveASR(f,c,b,eps/2.0,right)

def adaptiveSimpsonsRule(f,a,b,eps):
"Calculate integral of f from a to b with max error of eps."
return recursiveASR(f,a,b,eps,simpsonsRule(f,a,b))

def invx(x):
return 1.0 / x

print("Simpson integral : ", \
adaptiveSimpsonsRule(invx,1.0,2.0,.000000001))
print("Exact value ln(2): ", math.log(2.0))
print("Value of epsilon : ", .000000001)

------------------------------------------------------------

kind regards, Antti J Ylikoski
Helsinki, Finland, the EU
http://www.tkk.fi/~ajy/
http://www.tkk.fi/~ajy/diss.pdf
antti.y...@gmail.com

Tim Roberts

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Apr 12, 2012, 2:07:37 AM4/12/12

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Kiuhnm <kiuhnm03.4t.yahoo.it> wrote:
>
>That won't do. A good example is when you pass a function to re.sub, for
>instance.

This is an odd request.

I often pass functions to functions in order to simulate a C switch
statement, such as in a language translator:

commands = {
'add': doAdd,
'subtract' : doSubtract,
'multiply' : doMultiply,
'divide' : doDivide
}

nextCommand = parseCommandLine( line )
invokeCommand( commands[NextCommand] )
--
Tim Roberts, ti...@probo.com
Providenza & Boekelheide, Inc.

Kiuhnm

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Apr 12, 2012, 11:48:44 AM4/12/12

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On 4/11/2012 16:01, Antti J Ylikoski wrote:
> On 9.4.2012 21:57, Kiuhnm wrote:
>> Do you have some real or realistic (but easy and self-contained)
>> examples when you had to define a (multi-statement) function and pass it
>> to another function?
>> Thank you.
>>
>> Kiuhnm
>
> A function to numerically integrate another function comes as follows:

[...]

Thank you.

Kiuhnm

Kiuhnm

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Apr 12, 2012, 11:58:43 AM4/12/12

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On 4/12/2012 8:07, Tim Roberts wrote:
> Kiuhnm<kiuhnm03.4t.yahoo.it> wrote:
>>
>> That won't do. A good example is when you pass a function to re.sub, for
>> instance.
>
> This is an odd request.

All shall be revealed :)

>
> I often pass functions to functions in order to simulate a C switch
> statement, such as in a language translator:
>
> commands = {
> 'add': doAdd,
> 'subtract' : doSubtract,
> 'multiply' : doMultiply,
> 'divide' : doDivide
> }
>
> nextCommand = parseCommandLine( line )
> invokeCommand( commands[NextCommand] )

I like that very much. Thank you.

Kiuhnm

Jan Kuiken

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Apr 12, 2012, 1:29:56 PM4/12/12

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On 4/9/12 20:57 , Kiuhnm wrote:

> Do you have some real or realistic (but easy and self-contained)
> examples when you had to define a (multi-statement) function and pass it
> to another function?

I don't use it daily but the first argument of list.sort, i.e. the
compare function springs to mind.

Jan Kuiken

Kiuhnm

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Apr 12, 2012, 7:07:57 PM4/12/12

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Yes, I guess there are times when a lambda is not enough and one needs
to define a real function.
Thanks.

Kiuhnm

Antti "Andy" Ylikoski

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Apr 13, 2012, 9:23:14 AM4/13/12

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Ref: numerical integration, one of the most famous methods probably is
the Romberg method:

http://en.wikipedia.org/wiki/Romberg%27s_method

the program in the Wikipedia article above is in C, but translating it
into Python would be very, very easy.

yours, Antti J Ylikoski