Hi,
I'd like to use closures to set allow a subroutine to set variables in its
caller, in leu of pointers. But I can't get it to work. I have the following
test pgm, but I can't understand its behaviour:
It uses a function p2() from the module modules.closure1b:
def p2 (proc):
proc ("dolly")
I thought the following worked like I expected it to:
from modules.closures1b import p2
def p1(msg1):
msg3 = "world"
print "p1: entered: ", msg1
def p11(msg2):
print "p11: entered: ", msg2
print msg1 + msg2 + msg3
print p2 (p11)
p1('hello')
$ python closures1c.py
p1: entered: hello
p11: entered: dolly
hellodollyworld
None
In other words, p1() is passed "hello" for msg1, "world" goes to the local msg3
and then p11() is invoked out of a remote module and it can access not only its
own argument (msg2) but also the variables local to p1(): "hellodollyworld".
But if I try to set the variable local to p1(), all of a sudden python seems to
forget everything we agreed on.
If I add this line to the script above:
msg3 = "goodbye"
as follows:
from modules.closures1b import p2
def p1(msg1):
msg3 = "world"
print "p1: entered: ", msg1
def p11(msg2):
print "p11: entered: ", msg2
print msg1 + msg2 + msg3
msg3 = "goodbye" # <- new
print p2 (p11)
p1('hello')
then all of a sudden, I get this:
p1: entered: hello
p11: entered: dolly
Traceback (most recent call last):
File "closures1c.py", line 13, in <module>
p1('hello')
File "closures1c.py", line 11, in p1
print p2 (p11)
File "/home/mellman/eg/python/modules/closures1b.py", line 2, in p2
proc ("dolly")
File "closures1c.py", line 9, in p11
print msg1 + msg2 + msg3
UnboundLocalError: local variable 'msg3' referenced before assignment
Huh? msg3 isn't more referenced than it was before!
Can anyone explain this to me?
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