Re: imported module no longer available

[Fredrik Lundh]

Jeff Dyke wrote:

I've come across an error that i'm not yet able to create a test case
for but wanted to get see if someone could shed light on this.
>
I have imported a module at the top of my file with
import mymodulename
>
this module is used many times in the current file successfully, but
then I attempt to use it one more time and get: UnboundLocalErr or:
local variable 'mymodulename' referenced before assignment

Let me guess: you've done

def myfunc():
print mymodulename
import mymodulename

or something similar? Getting an exception in this case is the excepted
behaviour; the reason being that a variable in a block only belongs to a
single scope. for the entire block. For details, see:

http://docs.python.org/ref/naming.html

Especially this section:

"If a name binding operation occurs anywhere within a code block, all
uses of the name within the block are treated as references to the
current block. This can lead to errors when a name is used within a
block before it is bound. This rule is subtle. Python lacks declarations
and allows name binding operations to occur anywhere within a code
block. The local variables of a code block can be determined by scanning
the entire text of the block for name binding operations."

To fix this, mark the name as global:

def myfunc():
global mymodulename # I mean the global name!
print mymodulename
import mymodulename

</F>