[Python-Dev] Reading Python source file

[Nick Coghlan]

On 18 November 2015 at 02:50, Guido van Rossum <guido at python.org> wrote:
> On Tue, Nov 17, 2015 at 8:20 AM, Serhiy Storchaka <storchaka at gmail.com> wrote:
>> On 17.11.15 11:59, M.-A. Lemburg wrote:
>>>
>>> I don't think these situations are all that common, though,
>>> so reading in the full source code before compiling it
>>> sounds like a reasonable approach.
>>>
>>> We use the same simplification in eGenix PyRun's emulation of
>>> the Python command line interface and it has so far not
>>> caused any problems.
>>
>> Current implementation of import system went the same way. As a result
>> importing the script as a module and running it with command line can have
>> different behaviours in corner cases.
>
> I'm confused. *Of course* these two behaviors differ, since Python
> uses a different __name__. Not sure how this relates to the REPL.

I think Serhiy was referring to the fact that importlib already reads
the entire file before compiling it - since the import abstraction
doesn't require modules to be files on disk, it uses the get_code()
API on the module loader internally, which is typically implemented by
calling get_source() and then passing the result to compile().

That behaviour is then inherited at the command line by both the -m
switch and the support for executing directories and zip archives.
When we consider that the "-c" switch also executes an in-memory
string, direct script execution is currently the odd one out in *not*
reading the entire source file into memory first, so Serhiy's proposed
simplification of the implementation makes sense to me.

Regards,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia