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Re: Converting a list of strings into a list of integers?

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On Sun, Jul 22, 2012 at 10:20 AM, Jan Riechers <janpeterr@freenet.de> wrote:
> Hi,
>
> I am not sure why everyone is using the for-iterator option over a "map",
> but I would do it like that:
>
> MODUS_LIST= map(int, options.modus_list)
>
> "map" works on a list and does commandX (here "int" conversion, use "str"
> for string.. et cetera) on sequenceY, returning a sequence. More in the help
> file.
>
> And if I'm not completely mistaken, it's also the quicker way to do
> performance wise. But I can't completely recall the exact reason.

My recollection is that map has the edge if you can pass it a built-in
or a C extension function, like int, or a complicated Python function
that you would end up calling anyway in the list comprehension.  The
situation changes though if you can write the comprehension to remove
the overhead of the Python function call.  For example:

map(lambda x: x+1, my_list)

[x+1 for x in my_list]

By performing the addition inline instead of calling a function to do
it, the list comprehension wins performance-wise in this scenario.  So
as a simple rule of thumb I will typically choose between map or a
comprehension based on whether I need to call a function or not (and
also based on how pretty or ugly the resulting code is).  Anything
further would just be premature optimization.  Also keep in mind that
in Python 3 map returns an iterator instead of a list, so for a fair
comparison you would have to compose the map with a list() call.

Cheers,
Ian

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Thread

Converting a list of strings into a list of integers? Tony the Tiger <tony@tiger.invalid> - 2012-07-22 10:29 -0500
  Re: Converting a list of strings into a list of integers? Roy Smith <roy@panix.com> - 2012-07-22 11:39 -0400
    Re: Converting a list of strings into a list of integers? Tony the Tiger <tony@tiger.invalid> - 2012-07-22 11:01 -0500
      Re: Converting a list of strings into a list of integers? Peter Otten <__peter__@web.de> - 2012-07-22 18:30 +0200
  Re: Converting a list of strings into a list of integers? Alister <alister.ware@ntlworld.com> - 2012-07-22 15:39 +0000
    Re: Converting a list of strings into a list of integers? Tony the Tiger <tony@tiger.invalid> - 2012-07-22 11:01 -0500
    Re: Converting a list of strings into a list of integers? Jan Riechers <janpeterr@freenet.de> - 2012-07-22 19:20 +0300
      Re: Converting a list of strings into a list of integers? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-22 17:01 +0000
        Re: Converting a list of strings into a list of integers? Jan Riechers <janpeterr@freenet.de> - 2012-07-22 20:27 +0300
      Re: Converting a list of strings into a list of integers? Grant Edwards <invalid@invalid.invalid> - 2012-07-23 14:27 +0000
        Re: Converting a list of strings into a list of integers? rusi <rustompmody@gmail.com> - 2012-07-23 08:31 -0700
    Re: Converting a list of strings into a list of integers? David Robinow <drobinow@gmail.com> - 2012-07-22 13:03 -0400
    Re: Converting a list of strings into a list of integers? Jan Riechers <janpeterr@freenet.de> - 2012-07-22 20:10 +0300
    Re: Converting a list of strings into a list of integers? Ian Kelly <ian.g.kelly@gmail.com> - 2012-07-22 11:16 -0600
  Re: Converting a list of strings into a list of integers? Paul Rubin <no.email@nospam.invalid> - 2012-07-22 10:03 -0700
  Re: Converting a list of strings into a list of integers? Dave Angel <d@davea.name> - 2012-07-22 21:03 -0400

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