Passing variables, creating instances, self, The mechanics and usage of classes: need explanation

call, class, instance-variables, parameter-passing, python

Solution

class Foo          (object):
    # ^class name  #^ inherits from object

    bar = "Bar" #Class attribute.

    def __init__(self):
        #        #^ The first variable is the class instance in methods.  
        #        #  This is called "self" by convention, but could be any name you want.
        #^ double underscore (dunder) methods are usually special.  This one 
        #  gets called immediately after a new instance is created.

        self.variable = "Foo" #instance attribute.
        print self.variable, self.bar  #<---self.bar references class attribute
        self.bar = " Bar is now Baz"   #<---self.bar is now an instance attribute
        print self.variable, self.bar  

    def method(self, arg1, arg2):
        #This method has arguments.  You would call it like this:  instance.method(1, 2)
        print "in method (args):", arg1, arg2
        print "in method (attributes):", self.variable, self.bar


a = Foo() # this calls __init__ (indirectly), output:
                 # Foo bar
                 # Foo  Bar is now Baz
print a.variable # Foo
a.variable = "bar"
a.method(1, 2) # output:
               # in method (args): 1 2
               # in method (attributes): bar  Bar is now Baz
Foo.method(a, 1, 2) #<--- Same as a.method(1, 2).  This makes it a little more explicit what the argument "self" actually is.

class Bar(object):
    def __init__(self, arg):
        self.arg = arg
        self.Foo = Foo()

b = Bar(a)
b.arg.variable = "something"
print a.variable # something
print b.Foo.variable # Foo

Problem

I just rewrote a working program into functions in a class and everything messed up. First, in the `__init__` section of the class I declared a bunch of variables with `self.variable=something`. Should I be able to access/modify these variables in every function of the class by using `self.variable` in that function? In other words, by declaring `self.variable` I have made these variables, global variables in the scope of the class right? If not, how do I handle self? Second, how do I correctly pass arguments to the class? Third, how do I call a function of the class outside of the class scope? Fouth, how do I create an Instance of the `class INITIALCLASS` in another `class OTHERCLASS`, passing variables from `OTHERCLASS` to `INITIALCLASS`? I want to call a function from `OTHERCLASS` with arguments from `INITIALCLASS`. What I've done so far is. ``` class OTHERCLASS(): def __init__(self,variable1,variable2,variable3): self.variable1=variable1 self.variable2=variable2 self.variable3=variable3 def someotherfunction(self): something=somecode(using self.variable3) self.variable2.append(something) print self.variable2 def somemorefunctions(self): self.variable2.append(variable1) class INITIALCLASS(): def __init__(self): self.variable1=value1 self.variable2=[] self.variable3='' self.DoIt=OTHERCLASS(variable1,variable2,variable3) def somefunction(self): variable3=Somecode #tried this self.DoIt.someotherfunctions() #and this DoIt.someotherfunctions() ``` I clearly didn't understand how to pass variables to classes or how to handle `self`, when to use it and when not. I probably also didn't understand how to properly create an instance of a class. In general I didn't understand the mechanics of classes so please help me and explain it to me like I have no idea (which I don't, it seems). Or point me to a thorough video, or readable tutorial. All I find on the web is super simple examples, that didn't help me much. Or just very short definitions of classes and class methods instances etc. I can send you my original code if you guys want, but its quite long.

Original source