PyWart: The problem with "print"

[Chris Angelico]

On Mon, Jun 3, 2013 at 3:04 AM, Rick Johnson
<rantingrickjohnson at gmail.com> wrote:
>  * Woefully inadequate because: Switching on or off the debug
>    messages is only valid in the current module that the
>    function was imported. What if you want to kill all
>    debugprint messages EVERYWHERE? Do you really want to edit
>    "debug = BOOLEAN" in every source file OR do something
>    stupid like import debugprint and edit the DEBUG constant
>    OR even dumber, edit the debugprint source code? GAWD NO!

Easy fix to this one. Instead of copying and pasting debugprint into
everything, have it in a module and import it everywhere. Then the
debug flag will be common to them all.

Oh, and you probably want to add **kwargs to debugprint, because the
print function does a lot more than sys.stdout.write does:

>>> print(1,2,3,4,sep='#')
1#2#3#4

>  * But even if you are willing to cope with all the "switch-
>    on-and-off" nonsense, are you willing to have you code
>    slowed by numerous calls to a dead function containing a
>    comparison that will always be false?

Hmm. Could be costly. Hey, you know, Python has something for testing that.

>>> timeit.timeit('debugprint("asdf")','def debugprint(*args):\n\tif not DEBUG: return\n\tprint(*args)\nDEBUG=False',number=1000000)
0.5838018519113444

That's roughly half a second for a million calls to debugprint().
That's a 580ns cost per call. Rather than fiddle with the language,
I'd rather just take this cost. Oh, and there's another way, too: If
you make the DEBUG flag have effect only on startup, you could write
your module thus:

if DEBUG:
  debugprint=print
else:
  def debugprint(*args,**kwargs):
    pass

So you can eliminate part of the cost there, if it matters to you. If
a half-microsecond cost is going to be significant to you, you
probably should be looking at improving other areas, maybe using
ctypes/cython, or possibly playing with the new preprocessor tricks
that have been being discussed recently. There's really no need to
change the language to solve one specific instance of this "problem".

ChrisA