function to do dynamic import?

[bambam]

import works in the main section of the module, but does
not work as I hoped when run inside a function.

That is, the modules import correctly, but are not visible to
the enclosing (global) scope.

Questions:
(1) Where can I read an explanation of this?
(2) Is there a work around?

BTW, sys.modules("filename") shows that the module is
loaded, I just don't know how to use it when loaded that
way. Also, if I import again at the global scope, the module
name becomes available.

Steve.

---.... exec "import gamel"
....

gim()
sys.modules["gamel"]

gamel NameError: name 'gamel' is not defined
exec "import gamel"
gamel

<module 'gamel' from 'c:\gamel.pyc'>

 

[attn.steven.kuo]

import works in the main section of the module, but does
not work as I hoped when run inside a function.

That is, the modules import correctly, but are not visible to
the enclosing (global) scope.

Questions:
(1) Where can I read an explanation of this?
(2) Is there a work around?

BTW, sys.modules("filename") shows that the module is
loaded, I just don't know how to use it when loaded that
way. Also, if I import again at the global scope, the module
name becomes available.

Steve.

(snipped)

This was recently discussed:

http://groups.google.com/group/comp.lang.python/msg/f6fcdf49710cb833

 

[J. Cliff Dyer]

import works in the main section of the module, but does
not work as I hoped when run inside a function.

That is, the modules import correctly, but are not visible to
the enclosing (global) scope.

Questions:
(1) Where can I read an explanation of this?
(2) Is there a work around?

BTW, sys.modules("filename") shows that the module is
loaded, I just don't know how to use it when loaded that
way. Also, if I import again at the global scope, the module
name becomes available.

Steve.

All you have done in this function is bind the module to the name gamel
within the scope of the function. As soon as the function exits, the
module goes out of scope. If you want to use it externally, return the
module.

def: gim():
import gamel
return gamelThis will have to change to

gamel = gim()

and the rest should work as expected.

sys.modules["gamel"]

gamel

NameError: name 'gamel' is not defined
<module 'gamel' from 'c:\gamel.pyc'>

 

[Steve Holden]

import works in the main section of the module, but does
not work as I hoped when run inside a function.

That is, the modules import correctly, but are not visible to
the enclosing (global) scope.

Questions:
(1) Where can I read an explanation of this?
(2) Is there a work around?

BTW, sys.modules("filename") shows that the module is
loaded, I just don't know how to use it when loaded that
way. Also, if I import again at the global scope, the module
name becomes available.

There's not much wrong with doing this, since it gives you the best of
both worlds. But you mean sys.modules["filename"], don't you?

... exec "import gamel"
...

gim()
sys.modules["gamel"]

gamel NameError: name 'gamel' is not defined
exec "import gamel"
gamel

<module 'gamel' from 'c:\gamel.pyc'>

Whoa there! There's a lot of difference between "importing a module
inside a function" and "executing an import statement inside a function".

If you want to do dynamic imports then the __import__ function is what
you need. Trying to use exec like that is a bad idea unless you clearly
understand the relationship between the different namespaces involved.
In fact, trying to use exec at all is a bad idea until you understand
Python better, and even then it's not often a terrific idea.

Think of exec more as a hack of last resort than the first tool to reach
for to solve a problem.

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
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[bambam]

(snipped)

This was recently discussed:

http://groups.google.com/group/comp.lang.python/msg/f6fcdf49710cb833

def gim():
exec "global gamel"
exec "import gamel"

Unfortunately, does not have the desired effect.
Steve.

 

[bambam]

import works in the main section of the module, but does
not work as I hoped when run inside a function.

That is, the modules import correctly, but are not visible to
the enclosing (global) scope.

Questions:
(1) Where can I read an explanation of this?
(2) Is there a work around?

BTW, sys.modules("filename") shows that the module is
loaded, I just don't know how to use it when loaded that
way. Also, if I import again at the global scope, the module
name becomes available.

Steve.

All you have done in this function is bind the module to the name gamel
within the scope of the function. As soon as the function exits, the
module goes out of scope. If you want to use it externally, return the
module.

def: gim():
import gamel
return gamelThis will have to change to

gamel = gim()

and the rest should work as expected.

sys.modules["gamel"]

gamel

NameError: name 'gamel' is not defined

exec "import gamel"
gamel

<module 'gamel' from 'c:\gamel.pyc'>

def: gim():
import gamel
return gamel

Unfortunately, it needs to do dynamic import: I can't list
all of the possible import modules because they are unknown
until runtime.

Steve.

 

[bambam]

import works in the main section of the module, but does
not work as I hoped when run inside a function.

That is, the modules import correctly, but are not visible to
the enclosing (global) scope.

Questions:
(1) Where can I read an explanation of this?
(2) Is there a work around?

BTW, sys.modules("filename") shows that the module is
loaded, I just don't know how to use it when loaded that
way. Also, if I import again at the global scope, the module
name becomes available.

There's not much wrong with doing this, since it gives you the best of
both worlds. But you mean sys.modules["filename"], don't you?

def gim():

... exec "import gamel"
...

gim()
sys.modules["gamel"]

gamel

NameError: name 'gamel' is not defined

exec "import gamel"
gamel

<module 'gamel' from 'c:\gamel.pyc'>

Whoa there! There's a lot of difference between "importing a module inside
a function" and "executing an import statement inside a function".

If you want to do dynamic imports then the __import__ function is what you
need. Trying to use exec like that is a bad idea unless you clearly
understand the relationship between the different namespaces involved. In
fact, trying to use exec at all is a bad idea until you understand Python
better, and even then it's not often a terrific idea.

Think of exec more as a hack of last resort than the first tool to reach
for to solve a problem.

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
--------------- Asciimercial ------------------
Get on the web: Blog, lens and tag the Internet
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----------- Thank You for Reading -------------

Yes, sys.modules["filename"], unfortunately, same mistake
made already 4 or 5 times before I typed this, and still hadn't
learned...many years working in an environment where the
distinction was not important. Sorry.

def gim(self):
for gamel in self.gamel_list:
__import__(gamel['file'])

Works as hoped for. I did a web search for 'dynamic import' and
the only examples I found used exec.

Thanks

Steve.

 

[Steve Holden]

bambam wrote:
[...]

def gim(self):
for gamel in self.gamel_list:
__import__(gamel['file'])

Works as hoped for. I did a web search for 'dynamic import' and
the only examples I found used exec.

Thanks

Cool. You're getting there!

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
--------------- Asciimercial ------------------
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----------- Thank You for Reading -------------

 

[Peter Otten]

Am Wed, 12 Sep 2007 11:54:51 +1000 schrieb bambam:

def gim():
exec "global gamel"
exec "import gamel"

Unfortunately, does not have the desired effect.
Steve.

Both statements have to be part of a single exec:

def gim():
modulename = "gamel" # determined at runtime
exec "global %s; import %s" % (modulename, modulename)

It may work, but it is still a bad idea to create global variables with a
name not known until runtime.

Peter