On Wed, Feb 07, 2001 at 11:55:20AM +0800, LUK ShunTim wrote:
>
> \begin{quote}
>
> ActivePython 2.0, build 202 (ActiveState Tool Corp.)
> based on Python 2.0 (#8, Oct 19 2000, 11:30:05) [MSC 32 bit (Intel)] on
> win32
> Type "copyright", "credits" or "license" for more information.
> >>> dir()
> ['__builtins__', '__doc__', '__name__']
> >>> dir(site)
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> NameError: There is no variable named 'site'
> >>> import site
> >>> dir(site)
> ['_Printer', '__builtin__', '__builtins__', '__doc__', '__file__',
> '__name__', '
> _test', 'addpackage', 'addsitedir', 'encoding', 'here', 'makepath',
> 'os', 'prefi
> x', 'prefixes', 'sitedir', 'sitedirs', 'sys']
> >>>
>
> \end{quote}
>
> Why doesn't the first dir(site) list the names from the site module?
The imported site module (or more specifically an object named 'site'
refering to the imported site module object) is not placed in the '__main__'
namespace (this is the namespace that gets listed by default with "dir()")
When you "import" a module, Python first checks it cache to see if the module
has already been imported, only reloads it if necessary, and then sets up a
reference in the current namespace. You can see the cache of loaded modules
in sys.modules so...
D:\>python
ActivePython 2.0, build 202 (ActiveState Tool Corp.)
based on Python 2.0 (#8, Oct 19 2000, 11:30:05) [MSC 32 bit (Intel)] on win32
Type "copyright", "credits" or "license" for more information.
>>> dir()
['__builtins__', '__doc__', '__name__']
So far there are no modules in the __main__ namespace.
>>> import sys
>>> dir()
['__builtins__', '__doc__', '__name__', 'sys']
Now a ref to the sys module has been added to the __main__ namespace.
>>> sys.modules
{'win32api': <module 'win32api' from 'D:\apps\Python20\win32\win32api.pyd'>, 'os
.path': <module 'ntpath' from 'd:\apps\python20\lib\ntpath.pyc'>, 'os': <module
'os' from 'd:\apps\python20\lib\os.pyc'>, 'exceptions': <module 'exceptions' (bu
ilt-in)>, '__main__': <module '__main__' (built-in)>, 'ntpath': <module 'ntpath'
from 'd:\apps\python20\lib\ntpath.pyc'>, 'nt': <module 'nt' (built-in)>, 'sys':
<module 'sys' (built-in)>, '__builtin__': <module '__builtin__' (built-in)>, 's
ite': <module 'site' from 'd:\apps\python20\lib\site.pyc'>, 'signal': <module 's
ignal' (built-in)>, 'UserDict': <module 'UserDict' from 'd:\apps\python20\lib\us
erdict.pyc'>, 'stat': <module 'stat' from 'd:\apps\python20\lib\stat.pyc'>}
You can see that the 'sys' and 'site' modules (among others) have been
loaded.
>>> import site
>>> dir()
['__builtins__', '__doc__', '__name__', 'site', 'sys']
Now we have a reference to the site modules in the __main__ namespace.
>>> dir(site)
['_Printer', '__builtin__', '__builtins__', '__doc__', '__file__', '__name__', '
_test', 'addpackage', 'addsitedir', 'encoding', 'here', 'makepath', 'os',
'prefix', 'prefixes', 'sitedir', 'sitedirs', 'sys']
Cheers,
Trent
--
Trent Mick
[EMAIL PROTECTED]
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