Interesting Problem

MRAB python at mrabarnett.plus.com
Wed Jan 20 17:38:07 CET 2010


Victor Subervi wrote:
> Hi;
> I think I finally have an interesting problem for y'all. I need to 
> import a script from a lower dir, forcing me to change dirs:
> 
> cwd = os.getcwd()
> os.chdir('%s/..' % cwd)
> sys.path.append(os.getcwd())
> from templateFrame import top, bottom
> os.chdir(cwd)
> 
There's no need to actually change current directory. Just do this:

sys.path.append(os.path.dirname(os.getcwd()))
from templateFrame import top, bottom

> Because I've found I must do my form evaluations *before* changing dir 
> as above, I am forced to call these values as globals:
> 
> form = cgi.FieldStorage()
> store = form.getfirst('store')
> cat = form.getfirst('cat')
> id = form.getfirst('id')
> pkg = form.getfirst('pkg')
> patientID = form.getfirst('patientID')
> 
> Now, apparently because of python's problem with globals, when I call 
> "id" as follows:
> 
> cursor.execute('select ProductID from productsPackages where 
> PackageID=%s' % id)
> 
> I get the following error:
> 
> /var/www/html/angrynates.com/cart/Store_frame2.py 
> <http://angrynates.com/cart/Store_frame2.py>
>   135   cursor.close()
>   136   bottom()
>   137
>   138 Store_frame2()
>   139
> Store_frame2 = <function Store_frame2>
>  /var/www/html/angrynates.com/cart/Store_frame2.py 
> <http://angrynates.com/cart/Store_frame2.py> in Store_frame2()
>   119     printAProduct()
>   120   else:
>   121     cursor.execute('select ProductID from productsPackages where 
> PackageID=%s' % id)
>   122     for id in [itm[0] for itm in cursor]:
>   123       printAProduct(id)
> global cursor = <MySQLdb.cursors.Cursor object>, cursor.execute = <bound 
> method Cursor.execute of <MySQLdb.cursors.Cursor object>>, global id = '1'
> 
> UnboundLocalError: local variable 'id' referenced before assignment
>       args = ("local variable 'id' referenced before assignment",)
> 
> Full code below. Please advise.
> 
Line 121 refers to 'id', but line 122 assigns to 'id' (the 'for' loop).

In a function, if you assign to a variable then that variable defaults
to being local. You're trying to use the local variable before assigning
a value to it. Having a local variable called 'id' means that you can't
refer to the global variable of the same name.

You're also assigning to 'i' on line 113, but not referring to it
elsewhere in the function.



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