On 09/06/2005, at 8:04 AM, Nick wrote:
Graham Dumpleton wrote:
On 09/06/2005, at 12:29 AM, Nick wrote:
but I just want to be clear that I don't think mod_python should
install any import hooks. That would probably be annoying to
seasoned Python programmers, and really a pain in the butt for me
specifically.
Curious to know why you think this would be annoying to seasoned
Python
programmers and a pain in the butt to yourself.
As I mentioned before, as a programmer I would want mod_python to be
an API for apache in Python, with no special alteration of how Python
works as advertised in the Python documentation. Installing import
hooks bypasses the Python import functionality as it's documented, and
in my opinion is not necessary to use mod_python as an API for apache.
The apache.import_module() method is already currently used to perform
the
top level import of a handler module and already behaves differently to
a
standard "import", so even without an import hook you already have a
problem.
While it may be convenient for some people to have an import hook that
will automagically reload a module when it changes on disk, that's
*not* how Python works, and would be unexpected behaviour for a Python
programmer. That's like saying that since most people want to parse
the input stream as form data, let's automatically parse it and put it
into req.form. But mod_python doesn't do that. You have to use
utils.FieldStorage.
FWIW, if you use mod_python.publisher form parameters are always
decoded into
req.form regardless of whether you use them and actually can cause a
few problems.
In Vampire I have demonstrated though that lazy form evaluation can be
implemented,
with form parameters only being decoded in the prototype if the handler
actually
indicates by way of defining form arguments that it wants them.
For my own applications I take advantage of Python's internal import
routine because it is in C and therefore much faster than any pure
Python implementation (try benchmarking an import hook in ihooks and
you'll see how slow it is).
The ihooks module is deprecated and is not used in any way in the new
style import
hooks mechanism in Python. The new style import mechanism is still
almost all written
in C from what I can tell, with call outs to Python code only in those
specific spots
where the now minimal hooks are allowed for a user defined module
importer and loader.
It isn't as bad as you make out, the general runtime cost of your own
code, Apache
and network I/O is still going to greatly exceed any minor cost of the
import hooks.
I want to inspect sys.modules, and that's where I expect imports to
go. I don't want to bypass an import mechanism that works differently
just to get back to Python's; that's counter-intuitive. Plus, it'll
make reuse a pain, because I'll have to write modules with special
checks to see if I'm in mod_python or do something else when not.
As I mentioned before, the import hook would only come into play in a
specific
context. It doesn't touch normal imports of stuff from the Python
installation
or site packages directory, or in practice any modules of your own
which you have
placed on sys.path somewhere. As such, no special checks are required,
as general
utility modules wouldn't make use of it.
The intent is that the import hooks are a convenience in some very
specific
cases related to the handler modules as they reside in document tree.
The idea
is that in general people wouldn't rely on them. You cannot get away
from using
it though if you want to use a package like Cheetah Templates and still
want
to use automatic module reloading, as it generates code which uses
"import"
and it isn't possible to change that to use a mod_python specific module
loading function unless you are prepared to rewrite bits of Cheetah
itself.
I just don't think default import hooks are necessary to make
mod_python generally useful to people. I can certainly understand
people's needs for something more flexible than Python's stock
importer when writing applications, and there's always an option to
add a module to mod_python that can let people do exactly that. I
just don't want it out of the box.
Even in Vampire where I have the import hook stuff working, it isn't on
by default
and I would not suggest that it should be on by default.
Graham
