Python 3 Accessing variable result from another Class - function

Question

I have a little problem with a variable update.
I have my variable declared in my first function as such self.TestVar = 0
then if a certain count ==2 self.TestVar = 2
in a second function (in the same class) but called from within another class I want returning self.TestVar. no way.
AttributeError: 'ThndClass' object has no attribute 'TestVar'
I am most certainly not doing the good way, all I want is accessing self.TestVar = 2 from my other class that's it's but I can't find a proper way to do so in Python.
It looks like my issue is that I get my self.TestVar = 2 in a "if" statement which make it live in another scope (or I might be wrong).
import sys
from PIL import Image
from PyQt4 import QtCore, QtGui
class MainWindow(QtGui.QWidget):
def __init__(self):
super(MainWindow, self).__init__()
self.initUI()
def initUI(self):
self.TestVar = 0
self.TheCount = 2
if self.TheCount ==2:
self.TestVar = 2
ThndClass()
def Getit(self):
print("called correctly")
print(self.TestVar)
return self.TestVar
def main():
app = QtGui.QApplication([])
mw = MainWindow()
sys.exit(app.exec_())
class ThndClass(QtGui.QWidget):
def __init__(self):
super(ThndClass, self).__init__()
self.initUI2()
def initUI2(self):
print("Class Called")
print(MainWindow.Getit(self))
if __name__ == '__main__':
main()
If I remove the 2nd Class call :
import sys
from PIL import Image
from PyQt4 import QtCore, QtGui
class MainWindow(QtGui.QWidget):
def __init__(self):
super(MainWindow, self).__init__()
self.initUI()
def initUI(self):
self.TestVar = 0
self.TheCount = 2
if self.TheCount ==2:
self.TestVar = 2
self.Getit()
def Getit(self):
print("called correctly")
print(self.TestVar)
return self.TestVar
def main():
app = QtGui.QApplication([])
mw = MainWindow()
sys.exit(app.exec_())
if __name__ == '__main__':
main()
This works correctly, but I want to be able to call def Getit() from another class and get my result. Or simply get a way to directly access self.TestVar from my other class.

Answer 1

When you call
MainWindow.Getit(self)
in ThndClass.initUI2, you are treating MainWindow and ThndClass interchangeably, when they do not have the same attributes. Here is an actual minimal example:
class Parent():
def __init__(self):
pass
class Child1(Parent):
def __init__(self):
super().__init__()
self.foo = "foo"
def method(self):
print(type(self))
print(self.foo)
class Child2(Parent):
def __init__(self):
super().__init__()
self.bar = "bar"
c1 = Child1()
Child1.method(c1) # pass Child1 instance to Child1 instance method
c2 = Child2()
Child1.method(c2) # pass Child2 instance to Child1 instance method
and full output:
<class '__main__.Child1'> # gets a Child1 instance
foo # first call succeeds
<class '__main__.Child2'> # gets a Child2 instance (which doesn't have 'foo')
Traceback (most recent call last):
File "C:/Python34/so.py", line 25, in <module>
Child1.method(c2)
File "C:/Python34/so.py", line 11, in method
print(self.foo)
AttributeError: 'Child2' object has no attribute 'foo' # second call fails
However, as it is not clear what exactly the code is supposed to be doing, I can't suggest a fix. I don't know why you create but don't assign a ThndClass instance in MainWindow.initUI, for example.
Here is one possible fix; pass a Child1 instance to Child2.__init__, then use it either as an argument to Child2.method:
class Child2(Parent):
def __init__(self, c1): # provide Child1 instance as parameter
super().__init__()
self.bar = "bar"
self.method(c1) # pass instance to Child2.method
def method(self, c1):
c1.method() # call Child1.method with c1 as self parameter
(Note that c1.method() is equivalent to Child1.method(c1).)
or make it an instance attribute:
class Child2(Parent):
def __init__(self, c1): # provide Child1 instance as parameter
super().__init__()
self.bar = "bar"
self.c1 = c1 # make Child1 instance a Child2 instance attribute
self.method() # now no argument needed
def method(self):
self.c1.method() # call Child1.method with c1 as self parameter
(Note that self.c1.method() is equivalent to Child1.method(self.c1).)
In use (either way):
>>> c1 = Child1()
>>> c2 = Child2(c1)
<class '__main__.Child1'> # Child1.method gets a Child1 instance
foo # and is called successfully

Answer 2

Thank's to your help jonrsharpe here's my working code :)
import sys
from PIL import Image
from PyQt4 import QtCore, QtGui
class MainWindow(QtGui.QWidget):
def __init__(self):
super(MainWindow, self).__init__()
self.initUI()
def initUI(self):
self.TestVar = 0
self.TheCount = 2
if self.TheCount ==2:
self.TestVar = 2
Themain = self
ThndClass(Themain)
def Getit(self):
print("called correctly")
print(self.TestVar)
return self.TestVar
def main():
app = QtGui.QApplication([])
mw = MainWindow()
sys.exit(app.exec_())
class ThndClass(QtGui.QWidget):
def __init__(self, Themain):
super(ThndClass, self).__init__()
self.Themain = Themain
self.initUI2()
def initUI2(self):
print("Class Called")
print(self.Themain.Getit())
if __name__ == '__main__':
main()
All working good now : ) Thanks you very much !