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Re: Apparent magic number problem

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Colin J. Williams wrote:
> The program runs correctly under each version, but it runs more slowly 
> under 3.2.

> This is probably due to the fact that the .pyc file is created for the
> Python 2.7 execution.
 
> When Python 3.2 is run it fails to create a new .pyc file and if the 2.7
> .pyc is offered directly a magic number problem is reported.

(1) .pyc files are only created if a module is imported
(2) The 2.7 .pyc file is put alongside the .py file whereas the 3.2 .pyc is 
put into the __pycache__ subfolder. No clash can occur.

A simple example:

$ ls
mod.py
$ cat mod.py
print("hello world")

Run it; no pyc is created:

$ python2.7 mod.py
hello world
$ ls
mod.py

Import it using 2.7:

$ python2.7 -c 'import mod'
hello world
$ ls
mod.py  mod.pyc

Import it using 3.2:

$ python3.2 -c 'import mod'
hello world
$ ls
mod.py  mod.pyc  __pycache__
$ ls __pycache__/
mod.cpython-32.pyc

Run the compiled code:

$ python2.7 mod.pyc
hello world
$ python3.2 __pycache__/mod.cpython-32.pyc 
hello world

But I'm with Steven, it's unlikely that the module compilation phase is 
responsible for a noticeable slowdown.

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Thread

Apparent  magic number problem "Colin J. Williams" <cjw@ncf.ca> - 2013-03-08 19:48 -0500
  Re: Apparent  magic number problem Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-09 05:22 +0000
  Re: Apparent  magic number problem Peter Otten <__peter__@web.de> - 2013-03-09 09:51 +0100
    Re: Apparent  magic number problem "Colin J. Williams" <cjw@ncf.ca> - 2013-03-09 10:16 -0500
      Re: Apparent  magic number problem Peter Otten <__peter__@web.de> - 2013-03-10 11:56 +0100

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