[Python-Dev] Criticism of execfile() removal in Python3

Paul Sokolovsky pmiscml at gmail.com
Tue Jun 10 04:23:12 CEST 2014


I was pleasantly surprised with the response to recent post about
MicroPython implementation details 
(https://mail.python.org/pipermail/python-dev/2014-June/134718.html). I
hope that discussion means that posts about alternative implementations
are not unwelcome here, so I would like to bring up another (of many)
issues we faced while implementing MicroPython.

execfile() builtin function was removed in 3.0. This brings few

1. It hampers interactive mode - instead of short and easy to type
execfile("file.py") one needs to use exec(open("file.py").read()). I'm
sure that's not going to bother a lot of people - after all, the
easiest way to execute a Python file is to drop back to shell and
restart python with file name, using all wonders of tab completion. But
now imagine that Python interpreter runs on bare hardware, and its REPL
is the only shell. That's exactly what we have with MicroPython's
Cortex-M port. But it's not really MicroPython-specific, there's
CPython port to baremetal either - http://www.pycorn.org/ .

2. Ok, assuming that exec(open().read()) idiom is still a way to go,
there's a problem - it requires to load entire file to memory. But
there can be not enough memory. Consider 1Mb file with 900Kb comments
(autogenerated, for example). execfile() could easily parse it, using
small buffer. But exec() requires to slurp entire file into memory, and
1Mb is much more than heap sizes that we target.

Comments, suggestions? Just to set a productive direction, please
kindly don't consider the problems above as MicroPython's. I very much
liked how last discussion went: I was pointed that
https://docs.python.org/3/reference/index.html is not really a CPython
reference, it's a *Python* reference, and there were even motion to
clarify in it some points which came out from MicroPython discussion.
So, what about https://docs.python.org/3/library/index.html - is it
CPython, or Python standard library specification? Assuming the latter,
what we have is that, by removal of previously available feature,
*Python* became less friendly for interactive usage and less scalable.

 Paul                          mailto:pmiscml at gmail.com

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