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Re: is there any principle when writing python function

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smith jack wrote:

> i have heard that function invocation in python is expensive, but make
> lots of functions are a good design habit in many other languages, so
> is there any principle when writing python function?

It's hard to discuss in the abstract.  A function should perform a 
recognizable step in solving the program's problem.  If you prepared to 
write your program by describing each of several operations the program 
would have to perform, then you might go on to plan a function for each of 
the described operations.  The high-level functions can then be analyzed, 
and will probably lead to functions of their own.

Test-driven development encourages smaller functions that give you a better 
granularity of testing.  Even so, the testable functions should each perform 
one meaningful step of a more general problem.

> for example, how many lines should form a function?
Maybe as few as one.

def increase (x, a):
    return x+a

is kind of stupid, but a more complicated line

def expand_template (bitwidth, defs):
	'''Turn Run-Length-Encoded list into bits.'''
	return np.array (sum (([bit]*(count*bitwidth) for count, bit in 
defs), []), np.int8)

is the epitome of intelligence.  I wrote it myself.  Even increase might be 
useful:

def increase (x, a):
    return x + a * application_dependent_quantity

`increase` has become a meaningful operation in the imaginary application 
we're discussing.


For an upper bound, it's harder to say.  If you read to the end of a 
function and can't remember how it started, or what it did in between, it's 
too big.  If you're reading on your favourite screen, and the end and the 
beginning are more than one page-scroll apart, it might be too big.  If it's 
too big, factoring it into sub-steps and making functions of some of those 
sub-steps is the fix.

	Mel.

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is there any principle when writing python function smith jack <thinke365@gmail.com> - 2011-08-23 19:59 +0800
  Re: is there any principle when writing python function Peter Otten <__peter__@web.de> - 2011-08-23 14:20 +0200
    Re: is there any principle when writing python function Roy Smith <roy@panix.com> - 2011-08-23 08:56 -0400
  Re: is there any principle when writing python function Mel <mwilson@the-wire.com> - 2011-08-23 08:53 -0400
  Re: is there any principle when writing python function Roy Smith <roy@panix.com> - 2011-08-23 08:55 -0400
  Re: is there any principle when writing python function Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2011-08-23 15:00 +0200
  Re: is there any principle when writing python function Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-24 01:22 +1000
    Re: is there any principle when writing python function Terry Reedy <tjreedy@udel.edu> - 2011-08-23 14:29 -0400
      Re: is there any principle when writing python function rantingrick <rantingrick@gmail.com> - 2011-08-23 13:22 -0700
      Re: is there any principle when writing python function Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-24 11:44 +1000
  Re: is there any principle when writing python function Seebs <usenet-nospam@seebs.net> - 2011-08-23 16:53 +0000
  Re: is there any principle when writing python function rantingrick <rantingrick@gmail.com> - 2011-08-23 10:02 -0700
    Re: is there any principle when writing python function alex23 <wuwei23@gmail.com> - 2011-08-23 20:05 -0700
    Re: is there any principle when writing python function alex23 <wuwei23@gmail.com> - 2011-08-23 20:08 -0700
      Re: is there any principle when writing python function Red John <redjohn367@gmail.com> - 2011-08-24 16:29 -0700
  Re: is there any principle when writing python function ting@thsu.org - 2011-08-25 22:20 -0700
    Re: is there any principle when writing python function Roy Smith <roy@panix.com> - 2011-08-26 07:15 -0400
      Re: is there any principle when writing python function rantingrick <rantingrick@gmail.com> - 2011-08-26 08:20 -0700
        Re: is there any principle when writing python function John Gordon <gordon@panix.com> - 2011-08-26 15:40 +0000
          Re: is there any principle when writing python function rantingrick <rantingrick@gmail.com> - 2011-08-26 11:05 -0700
            Re: is there any principle when writing python function Chris Angelico <rosuav@gmail.com> - 2011-08-27 07:45 +1000
              Re: is there any principle when writing python function rantingrick <rantingrick@gmail.com> - 2011-08-26 15:26 -0700
              Re: is there any principle when writing python function Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-27 11:26 +1000
                Re: is there any principle when writing python function Chris Angelico <rosuav@gmail.com> - 2011-08-27 11:37 +1000
              Re: is there any principle when writing python function Roy Smith <roy@panix.com> - 2011-08-27 12:41 -0400
                Re: is there any principle when writing python function Chris Angelico <rosuav@gmail.com> - 2011-08-28 02:57 +1000
                Re: is there any principle when writing python function Emile van Sebille <emile@fenx.com> - 2011-08-27 10:27 -0700
                Re: is there any principle when writing python function Ben Finney <ben+python@benfinney.id.au> - 2011-08-28 07:57 +1000
                Re: is there any principle when writing python function Emile van Sebille <emile@fenx.com> - 2011-08-27 15:21 -0700
                Re: is there any principle when writing python function rantingrick <rantingrick@gmail.com> - 2011-08-27 16:01 -0700
                Re: is there any principle when writing python function Roy Smith <roy@panix.com> - 2011-08-27 19:09 -0400
                Re: is there any principle when writing python function Stephen Hansen <me+list/python@ixokai.io> - 2011-08-27 16:27 -0700
                Re: is there any principle when writing python function Chris Angelico <rosuav@gmail.com> - 2011-08-28 03:31 +1000
                Re: is there any principle when writing python function Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-28 06:27 +1000
                Re: is there any principle when writing python function Chris Angelico <rosuav@gmail.com> - 2011-08-28 06:38 +1000
                Re: is there any principle when writing python function Roy Smith <roy@panix.com> - 2011-08-27 17:09 -0400
        Re: is there any principle when writing python function Tobiah <tobiah@teranews.com> - 2011-08-26 08:48 -0700
          Re: is there any principle when writing python function Chris Angelico <rosuav@gmail.com> - 2011-08-27 02:10 +1000
            Re: is there any principle when writing python function Neil Cerutti <neilc@norwich.edu> - 2011-08-29 14:52 +0000
              Re: is there any principle when writing python function Chris Angelico <rosuav@gmail.com> - 2011-08-30 04:20 +1000
                Re: is there any principle when writing python function Neil Cerutti <neilc@norwich.edu> - 2011-08-29 18:40 +0000
                Re: is there any principle when writing python function Chris Angelico <rosuav@gmail.com> - 2011-08-30 05:02 +1000
                For some value of “sing” (was: is there any principle when writing python function) Ben Finney <ben+python@benfinney.id.au> - 2011-08-30 08:17 +1000
                Re: is there any principle when writing python function Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-08-29 23:20 -0700
          Re: is there any principle when writing python function Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-27 04:16 +1000
            Re: is there any principle when writing python function rantingrick <rantingrick@gmail.com> - 2011-08-26 15:37 -0700
  Re: is there any principle when writing python function harrismh777 <harmar@member.fsf.org> - 2011-08-27 23:51 -0500

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