Reload after an exception, not possible ?

[Stef Mientki]

hello,

I've a graphical application (wxPython),
where the code in the main GUI loop is given below.


1 JAL_Loaded = False
2 while len(App_Running) > 0:
3 if JALsPy_globals.State == SS_Run:
4 try:
5 if JAL_Loaded:
6 reload ( JAL_simulation_file )
7 else:
8 JAL_Loaded = True
9 import JAL_simulation_file
10 except JALsPy_globals.Reload_Exception:
11 JALsPy_globals.State = SS_Halt


The first time the while loop is entered,
JAL_Loaded is False (line 1),
and when I press some button,
the code will enter at line 8,
importing a module, that has executable code with an infinite loop.

To exit this infinite loop, an exception is generated (by a button press),
and program comes back in the above while-loop line (10,11,2).

So far so good.

Then I change the code in the imported file,
and when I start the engine again,
the flag JAL_Loaded is True, so I don't import,
but I reload the file.

Now I get the next exception
UnboundLocalError: local variable 'JAL_simulation_file' referenced before assignment

So obviously I can't reload but have to do an import again
(which makes the code much simpler ;-)
but I don't understand why the reload raises an exception ????

please enlighten me,
thanks,
Stef Mientki

 

[Steve Holden]

hello,

I've a graphical application (wxPython),
where the code in the main GUI loop is given below.


1 JAL_Loaded = False
2 while len(App_Running) > 0:
3 if JALsPy_globals.State == SS_Run:
4 try:
5 if JAL_Loaded:
6 reload ( JAL_simulation_file )
7 else:
8 JAL_Loaded = True
9 import JAL_simulation_file
10 except JALsPy_globals.Reload_Exception:
11 JALsPy_globals.State = SS_Halt


The first time the while loop is entered,
JAL_Loaded is False (line 1),
and when I press some button,
the code will enter at line 8,
importing a module, that has executable code with an infinite loop.

To exit this infinite loop, an exception is generated (by a button press),
and program comes back in the above while-loop line (10,11,2).

So far so good.

Then I change the code in the imported file,
and when I start the engine again,
the flag JAL_Loaded is True, so I don't import,
but I reload the file.

Now I get the next exception
UnboundLocalError: local variable 'JAL_simulation_file' referenced before assignment

So obviously I can't reload but have to do an import again
(which makes the code much simpler ;-)
but I don't understand why the reload raises an exception ????

You have an assignment to JAL_simulation_file elsewhere inside the same
function, later in the code. This means that Python will assume that it
is local to the function, but the import statement will affect the
module namespace rather than the function namespace.

In other words, your code is roughly equivalent to what follows, with
the added complexity that the illegal reference isn't triggered until
the second iteration of a loop.
.... print os
.... import os
.... os = "Something"
....Traceback (most recent call last):
File "<stdin>", line 1, in <module>

The solution? Don't assign to JAL_simulation_file, and the function will
use the local instead.

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
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[Steve Holden]

Steve Holden wrote:
[...]

The solution? Don't assign to JAL_simulation_file, and the function will
use the local instead.

Sorry, that last "local" should have been "global".

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
Many services currently offer free registration
----------- Thank You for Reading -------------

 

[Stef Mientki]

You have an assignment to JAL_simulation_file elsewhere inside the same
function,

No these are the only 2 uses of "JAL_simulation_file" in the whole project.

later in the code. This means that Python will assume that it

is local to the function, but the import statement will affect the
module namespace rather than the function namespace.

In other words, your code is roughly equivalent to what follows, with
the added complexity that the illegal reference isn't triggered until
the second iteration of a loop.

... print os
... import os
... os = "Something"
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>


The solution? Don't assign to JAL_simulation_file, and the function will
use the local instead.

The solution is much simpler, but I don't understand why the "import",
which really reloads the changed code in JAL_simulation_file,
works the second time :-(

2 while len(App_Running) > 0:
3 if JALsPy_globals.State == SS_Run:
4 try:
9 import JAL_simulation_file
10 except JALsPy_globals.Reload_Exception:
11 JALsPy_globals.State = SS_Halt

cheers,
Stef Mientki