[Python-Dev] Inconsistent behaviour in import/zipimport hooks

[Ulrich Berning]

Guido van Rossum schrieb:

>On 11/11/05, Ulrich Berning <ulrich.berning at desys.de> wrote:
>  
>
>>For instance, nobody would give the output of a C compiler a different
>>extension when different compiler flags are used.
>>    
>>
>
>But the usage is completely different. With C you explicitly manage
>when compilation happens. With Python you don't. When you first run
>your program with -O but it crashes, and then you run it again without
>-O to enable assertions, you would be very unhappy if the bytecode
>cached in a .pyo file would be reused!
>
>  
>
The other way round makes definitely more sense. At development time, I 
would never use Python with -O or -OO. I use it only at distribution 
time, after doing all the tests, to generate optimized bytecode.

However, this problem could be easily solved, if the value of 
Py_OptimizeFlag would be stored together with the generated bytecode. At 
import time, the cached bytecode would not be reused if the current 
value of Py_OptimizeFlag doesn't match the stored value (if the .py file 
isn't there any longer, we could either raise an exception or we could 
emit a warning and reuse the bytecode anyway). And if we do this a 
little bit more clever, we could refuse reusing optimized bytecode if we 
are running without -O or -OO and ignore assertions and docstrings in 
unoptimized bytecode when we are running with -O or -OO.

>>I would appreciate to see the generation of .pyo files completely
>>removed in the next release.
>>    
>>
>
>You seem to forget the realities of backwards compatibility. While
>there are ways to cache bytecode without having multiple extensions,
>we probably can't do that until Python 3.0.
>
>  
>
Please can you explain what backwards compatibility means in this 
context? Generated bytecode is neither upwards nor backwards compatible. 
No matter what I try, I always get a 'Bad magic number' when I try to 
import bytecode generated with a different Python version.
The most obvious software, that may depend on the existence of .pyo 
files are the various freeze/packaging tools like py2exe, py2app, 
cx_Freeze and Installer.  I haven't checked them in detail, but after a 
short inspection, they seem to be independent of the existence of .pyo 
files. I can't imagine that there is any other Python software, that 
depends on the existence of .pyo files, but maybe I'm totally wrong in 
this wild guess.

Ulli