Python: class called from another class can't access attribute

[Uchiya]

Sorry if the title is not correct, I don't know how to explain better.

I want the class EventHandler to be able to use/see the variable "file". How can I do that?


class app:
def __init__:
self.file=open("file.txt")
n=pyinotifier.threadedNotifier(blah, EventHandler())

def choosefiledialog(self):
#code to choose file

class EventHandler(pyinotify.ProcessEvent)
def IN_MODIFY(self,event)
#Stuff to do when event is received
file.something()

if __name__ = "main":
a=app()

[nzjethro]

Hi there, I'm quite new to Python, but I believe you could declare the file object as global, using


class spam:
global file
def eggs():
rest of code here

While this will work, I think most Python purist frown upon globals, and prefer to use set() and get() methods (my background is Java, so I may be calling them the wrong thing here).

[simeon87]

In some frameworks you can pass additional arguments to an event handler. In that case it would look like:


class app:
def __init__:
self.file=open("file.txt")
n=pyinotifier.threadedNotifier(blah, EventHandler(), self.file)

def choosefiledialog(self):
#code to choose file

class EventHandler(pyinotify.ProcessEvent)
def IN_MODIFY(self,event, f)
#Stuff to do when event is received
f.something()

if __name__ = "main":
a=app()

But if your framework doesn't support that then that's not possible. In that case you could pass the file to the event handler upon construction:


class app:
def __init__:
self.file=open("file.txt")
n=pyinotifier.threadedNotifier(blah, EventHandler(self.file))

def choosefiledialog(self):
#code to choose file

class EventHandler(pyinotify.ProcessEvent)
def __init__(self, f):
self.file = f
def IN_MODIFY(self,event)
#Stuff to do when event is received
self.file.something()

if __name__ = "main":
a=app()

Not necessarily the prettiest solution but it works. Otherwise you end up working with globals.

[Tony Flury]

You need to make sure your Event Handler Class knows about the instance of the app class - i would suggest passing the app class as a parameter as suggested by simeon87

I would not suggest the global route. You could have a singleton pattern - and do it properly via a singleton class and an access method, but i would go the parameter route.

I actually think that the global directive is something that Python has got very wrong - it encourages poor design and it is always possible to design code without globals.