Scott David Daniels wrote:
<div class="moz-text-flowed" style="font-family: -moz-fixed">Piet van
Oostrum wrote:
Peter Otten <__pete...@web.de> (PO) wrote:
PO> $ cat x.py
PO> import sys
PO> globals().update(zip(*(range(110),)*2))
PO> y = 42
PO> print __name__
PO> if __name__ == "__main__":
PO> a = b = 42
PO> print len(dir())
PO> from x import y as z
PO> try:
PO> print my_name
PO> except NameError, e:
PO> print 'unhandled NameError: "%s"' % e
PO> sys.exit()
PO> $ python x.py
PO> __main__
PO> 119
PO> x
PO> 117
PO> unhandled NameError: "name 'my_name' is not defined"
This is perfectly normal. python x.py command runs normally (although
the globals().update is a very weird thing to do), until the from x
import y command. Then x.py is loaded again but now as the module 'x'
instead of '__main__'. Python doesn't know it's the same file, and
actually it doesn't want to know. It only knows it when you do import
twice on the same file. Not when you run it as a main script first and
then imports it. **This is a thing you shouldn't do**.
There are now two namespaces: one for __main__ and one for x. These are
distinct and have no relationship.
The reason that the first number is 119 and the second is 117 is that
while importing x the variables a and b are not created.
After a bit more boiling down:
x.py:
import sys
y = 42
if __name__ == "__main__":
a = b = 42
print __name__, 'size', len(dir())
from x import y as z
print __name__, 'size', len(dir()), 'completed import of', z
try:
print my_name
except NameError, e:
print '%s found unhandled NameError: "%s"' % (__name__, e)
sys.exit()
produces:
__main__
__main__ size 8
x
x size 6
x size 7 completed import of 42
x found unhandled NameError: "name 'my_name' is not defined"
--Scott David Daniels
scott.dani...@acm.org
</div>
I already said this before - don't ever import the file you're using as
a script. Now that we have real names for these files, I can say it
more strongly.
If you use "import x" or its variant "from x import..." then *DO
NOT* run x.py as your main script.
You must have a separate script file that you run, and that nobody tries
to import.
Now, once you get past that problem, you'll probably have others. Why
on earth would you try to import a module from itself? The line:
from x import y as z
is probably equivalent to z=y
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