Rune Strand <[EMAIL PROTECTED]> wrote: > > those modules are already imported when Python gets to your code, so > > the only "overhead" you're saving is a little typing. > > I don't understand this. Could you please elaborate? - if sys or os > are not imported for any other causes how are they already imported?
The "other causes" are always present, since these modules include functionality Python always needs -- a fact that is no big secret, either. For example: you know (I assume and hope) that Python's import statement finds files to import along directories (and zipfiles) listed in sys.path -- so how do you think 'sys' itself can possibly get 'imported' in the first place, since the import mechanism depends on one of sys's attributes...? Answer: sys is a built-in module, compiled into the Python interpreter itself. There are several, see sys.builtin_file_names for a list. 'os' is a slightly different case -- it's not built-in, but gets imported anyway during startup because other modules need it anyway. In my build of Python 2.4.1, there are 16 built-in modules, and 9 others that aren't built-in but get imported at startup -- check sys.modules on your version for the total number of modules that are in memory by the time any code of yours runs. (This is with -S to inhibit Python from reading the site.py module, otherwise you might get more... but never, I believe, could you get fewer). > Maybe I'm wrong here, and accessing the filesystem and reading the > module into memory represents no cost. My mistake, in that case. Your mistake is due to a different case: the filesystem access and reading have ALREADY happened (for os; for sys, as I explained, the mechanism is different). Therefore, an import does NO such access and reading -- it just gets the module object from (e.g.) sys.modules['os']. > > wow. that's one lousy optimization... > > > here's a *shorter* piece of code, which is also readable and portable, and > > a lot easier to type on most keyboards: > > > import os > > __filename__ = os.path.basename(__file__) > > It may be lousy, but it requires no imports. And, as I said in the The point is that there's no substantial advantage to "requiring no imports". Python, if anything, already has too many built-ins -- once backwards compatibility can be broken (i.e., in 3.0), many of them should be moved to standard library modules, "requiring imports" (which are cheap operations anyway). The desire for MORE built-ins with no real advantage (since "requiring no imports" ISN'T a true advantage) is definitely misplaced. Alex -- http://mail.python.org/mailman/listinfo/python-list
