Related
How to define different addresses for class attributes and instance attributes?
This problem has bothered me for a long time, unless I delete the definition of the class attribute, but want to use the class attribute.
I have defined a dict with the same name in the class attribute and instance attribute. How can I make the memory address different? I tried a variety of methods to delete the content of the class attribute. Is there any other method?
My demo code is as follows:
class MyClass:
bar: dict = {}
def __init__(self):
bar: dict = {}
print(id(MyClass.bar))
a = MyClass()
print(id(a.bar))
1914627629760
1914627629760
class MyClass:
bar: dict = {}
def __init__(self):
self.bar = {}
print(id(MyClass.bar))
a = MyClass()
print(id(a.bar))
2318292079808
2318295104384
That said, I have no idea why we are doing this, and there is an almost 100% chance this will make whomever (next) maintains this codebase go insane within the next 2 years.
Explanation:
You are not "saving" your variable in your __init__() function.
Try running:
class MyClass:
def __init__(self):
self.a = 1 # setting attribute a to value 1
b = 2 # b is not an attribute, it's just a local variable
m = MyClass()
print(m.a) # this will work
print(m.b) # this will not
I have a situation like so...
class Outer(object):
def some_method(self):
# do something
class Inner(object):
def __init__(self):
self.Outer.some_method() # <-- this is the line in question
How can I access the Outer class's method from the Inner class?
You're trying to access Outer's class instance, from inner class instance. So just use factory-method to build Inner instance and pass Outer instance to it.
class Outer(object):
def createInner(self):
return Outer.Inner(self)
class Inner(object):
def __init__(self, outer_instance):
self.outer_instance = outer_instance
self.outer_instance.somemethod()
def inner_method(self):
self.outer_instance.anothermethod()
The methods of a nested class cannot directly access the instance attributes of the outer class.
Note that it is not necessarily the case that an instance of the outer class exists even when you have created an instance of the inner class.
In fact, it is often recommended against using nested classes, since the nesting does not imply any particular relationship between the inner and outer classes.
maybe I'm mad but this seems very easy indeed - the thing is to make your inner class inside a method of the outer class...
def do_sthg(self):
...
def mess_around(self):
outer_class_self = self
class Mooble():
def do_sthg_different(self):
...
outer_class_self.do_sthg()
Plus... "self" is only used by convention, so you could do this:
def do_sthg(self):
...
def mess_around(outer_class_self):
class Mooble():
def do_sthg_different(self):
...
outer_class_self.do_sthg()
It might be objected that you can't then create this inner class from outside the outer class... but this ain't true:
class Bumblebee():
def do_sthg(self):
print "sthg"
def give_me_an_inner_class(outer_class_self):
class Mooble():
def do_sthg_different(self):
print "something diff\n"
outer_class_self.do_sthg()
return Mooble
then, somewhere miles away:
blob = Bumblebee().give_me_an_inner_class()()
blob.do_sthg_different()
even push the boat out a bit and extend this inner class (NB to get super() to work you have to change the class signature of Mooble to class Mooble(object)).
class InnerBumblebeeWithAddedBounce(Bumblebee().give_me_an_inner_class()):
def bounce(self):
print "bounce"
def do_sthg_different(self):
super(InnerBumblebeeWithAddedBounce, self).do_sthg_different()
print "and more different"
ibwab = InnerBumblebeeWithAddedBounce()
ibwab.bounce()
ibwab.do_sthg_different()
later
mrh1997 raised an interesting point about the non-common inheritance of inner classes delivered using this technique. But it seems that the solution is pretty straightforward:
class Fatty():
def do_sthg(self):
pass
class InnerFatty(object):
pass
def give_me_an_inner_fatty_class(self):
class ExtendedInnerFatty(Fatty.InnerFatty):
pass
return ExtendedInnerFatty
fatty1 = Fatty()
fatty2 = Fatty()
innerFattyClass1 = fatty1.give_me_an_inner_fatty_class()
innerFattyClass2 = fatty2.give_me_an_inner_fatty_class()
print (issubclass(innerFattyClass1, Fatty.InnerFatty))
print (issubclass(innerFattyClass2, Fatty.InnerFatty))
I found this.
Tweaked to suite your question:
class Outer(object):
def some_method(self):
# do something
class _Inner(object):
def __init__(self, outer):
outer.some_method()
def Inner(self):
return _Inner(self)
I’m sure you can somehow write a decorator for this or something
related: What is the purpose of python's inner classes?
A few years late to the party.... but to expand on #mike rodent's wonderful answer, I've provided my own example below that shows just how flexible his solution is, and why it should be (or should have been) the accepted answer.
Python 3.7
class Parent():
def __init__(self, name):
self.name = name
self.children = []
class Inner(object):
pass
def Child(self, name):
parent = self
class Child(Parent.Inner):
def __init__(self, name):
self.name = name
self.parent = parent
parent.children.append(self)
return Child(name)
parent = Parent('Bar')
child1 = parent.Child('Foo')
child2 = parent.Child('World')
print(
# Getting its first childs name
child1.name, # From itself
parent.children[0].name, # From its parent
# Also works with the second child
child2.name,
parent.children[1].name,
# Go nuts if you want
child2.parent.children[0].name,
child1.parent.children[1].name
)
print(
# Getting the parents name
parent.name, # From itself
child1.parent.name, # From its children
child2.parent.name,
# Go nuts again if you want
parent.children[0].parent.name,
parent.children[1].parent.name,
# Or insane
child2.parent.children[0].parent.children[1].parent.name,
child1.parent.children[1].parent.children[0].parent.name
)
# Second parent? No problem
parent2 = Parent('John')
child3 = parent2.Child('Doe')
child4 = parent2.Child('Appleseed')
print(
child3.name, parent2.children[0].name,
child4.name, parent2.children[1].name,
parent2.name # ....
)
Output:
Foo Foo World World Foo World
Bar Bar Bar Bar Bar Bar Bar
Doe Doe Appleseed Appleseed John
Again, a wonderful answer, props to you mike!
You can easily access to outer class using metaclass: after creation of outer class check it's attribute dict for any classes (or apply any logic you need - mine is just trivial example) and set corresponding values:
import six
import inspect
# helper method from `peewee` project to add metaclass
_METACLASS_ = '_metaclass_helper_'
def with_metaclass(meta, base=object):
return meta(_METACLASS_, (base,), {})
class OuterMeta(type):
def __new__(mcs, name, parents, dct):
cls = super(OuterMeta, mcs).__new__(mcs, name, parents, dct)
for klass in dct.values():
if inspect.isclass(klass):
print("Setting outer of '%s' to '%s'" % (klass, cls))
klass.outer = cls
return cls
# #six.add_metaclass(OuterMeta) -- this is alternative to `with_metaclass`
class Outer(with_metaclass(OuterMeta)):
def foo(self):
return "I'm outer class!"
class Inner(object):
outer = None # <-- by default it's None
def bar(self):
return "I'm inner class"
print(Outer.Inner.outer)
>>> <class '__main__.Outer'>
assert isinstance(Outer.Inner.outer(), Outer)
print(Outer().foo())
>>> I'm outer class!
print(Outer.Inner.outer().foo())
>>> I'm outer class!
print(Outer.Inner().outer().foo())
>>> I'm outer class!
print(Outer.Inner().bar())
>>> I'm inner class!
Using this approach, you can easily bind and refer two classes between each other.
I've created some Python code to use an outer class from its inner class, based on a good idea from another answer for this question. I think it's short, simple and easy to understand.
class higher_level__unknown_irrelevant_name__class:
def __init__(self, ...args...):
...other code...
# Important lines to access sub-classes.
subclasses = self._subclass_container()
self.some_subclass = subclasses["some_subclass"]
del subclasses # Free up variable for other use.
def sub_function(self, ...args...):
...other code...
def _subclass_container(self):
_parent_class = self # Create access to parent class.
class some_subclass:
def __init__(self):
self._parent_class = _parent_class # Easy access from self.
# Optional line, clears variable space, but SHOULD NOT BE USED
# IF THERE ARE MULTIPLE SUBCLASSES as would stop their parent access.
# del _parent_class
class subclass_2:
def __init__(self):
self._parent_class = _parent_class
# Return reference(s) to the subclass(es).
return {"some_subclass": some_subclass, "subclass_2": subclass_2}
The main code, "production ready" (without comments, etc.). Remember to replace all of each value in angle brackets (e.g. <x>) with the desired value.
class <higher_level_class>:
def __init__(self):
subclasses = self._subclass_container()
self.<sub_class> = subclasses[<sub_class, type string>]
del subclasses
def _subclass_container(self):
_parent_class = self
class <sub_class>:
def __init__(self):
self._parent_class = _parent_class
return {<sub_class, type string>: <sub_class>}
Explanation of how this method works (the basic steps):
Create a function named _subclass_container to act as a wrapper to access the variable self, a reference to the higher level class (from code running inside the function).
Create a variable named _parent_class which is a reference to the variable self of this function, that the sub-classes of _subclass_container can access (avoids name conflicts with other self variables in subclasses).
Return the sub-class/sub-classes as a dictionary/list so code calling the _subclass_container function can access the sub-classes inside.
In the __init__ function inside the higher level class (or wherever else needed), receive the returned sub-classes from the function _subclass_container into the variable subclasses.
Assign sub-classes stored in the subclasses variable to attributes of the higher level class.
A few tips to make scenarios easier:
Making the code to assign the sub classes to the higher level class easier to copy and be used in classes derived from the higher level class that have their __init__ function changed:
Insert before line 12 in the main code:
def _subclass_init(self):
Then insert into this function lines 5-6 (of the main code) and replace lines 4-7 with the following code:
self._subclass_init(self)
Making subclass assigning to the higher level class possible when there are many/unknown quantities of subclasses.
Replace line 6 with the following code:
for subclass_name in list(subclasses.keys()):
setattr(self, subclass_name, subclasses[subclass_name])
Example scenario of where this solution would be useful and where the higher level class name should be impossible to get:
A class, named "a" (class a:) is created. It has subclasses that need to access it (the parent). One subclass is called "x1". In this subclass, the code a.run_func() is run.
Then another class, named "b" is created, derived from class "a" (class b(a):). After that, some code runs b.x1() (calling the sub function "x1" of b, a derived sub-class). This function runs a.run_func(), calling the function "run_func" of class "a", not the function "run_func" of its parent, "b" (as it should), because the function which was defined in class "a" is set to refer to the function of class "a", as that was its parent.
This would cause problems (e.g. if function a.run_func has been deleted) and the only solution without rewriting the code in class a.x1 would be to redefine the sub-class x1 with updated code for all classes derived from class "a" which would obviously be difficult and not worth it.
Do you mean to use inheritance, rather than nesting classes like this? What you're doing doesn't make a heap of sense in Python.
You can access the Outer's some_method by just referencing Outer.some_method within the inner class's methods, but it's not going to work as you expect it will. For example, if you try this:
class Outer(object):
def some_method(self):
# do something
class Inner(object):
def __init__(self):
Outer.some_method()
...you'll get a TypeError when initialising an Inner object, because Outer.some_method expects to receive an Outer instance as its first argument. (In the example above, you're basically trying to call some_method as a class method of Outer.)
Another possibility:
class _Outer (object):
# Define your static methods here, e.g.
#staticmethod
def subclassRef ():
return Outer
class Outer (_Outer):
class Inner (object):
def outer (self):
return _Outer
def doSomething (self):
outer = self.outer ()
# Call your static mehthods.
cls = outer.subclassRef ()
return cls ()
What we can do is pass the self variable of Outer Class inside the Inner Class as Class Argument and Under Outer init initialise the Inner Class with Outer self passed into Inner
class Outer:
def __init__(self):
self.somevalue=91
self.Inner=self.Inner(self)
def SomeMethod(self):
print('This is Something from Outer Class')
class Inner:
def __init__(self,Outer)
self.SomeMethod=Outer.SomeMethod
self.somevalue=Outer.somevalue
def SomeAnotherMethod(self):
print(self.somevalue)
self.SomeMethod()
>>>f=Outer()
>>>f.Inner.SomeAnotherMethod()
91
This is Something from Outer Class
Now After running this function it Works
Expanding on #tsnorri's cogent thinking, that the outer method may be a static method:
class Outer(object):
#staticmethod
def some_static_method(self):
# do something
class Inner(object):
def __init__(self):
self.some_static_method() # <-- this will work later
Inner.some_static_method = some_static_method
Now the line in question should work by the time it is actually called.
The last line in the above code gives the Inner class a static method that's a clone of the Outer static method.
This takes advantage of two Python features, that functions are objects, and scope is textual.
Usually, the local scope references the local names of the (textually) current function.
...or current class in our case. So objects "local" to the definition of the Outer class (Inner and some_static_method) may be referred to directly within that definition.
You may create a class, to decorate inner classes. In this case #inner.
Since this a decorator: Outer.A = inner(Outer.A). Once your code requires Outer.A it will be executed inner.__get__ method, which returns the original class (A) with a new attribute set on it: A.owner = Outer.
A classmethod in class A, in this case def add(cls, y=3), may use new attribute owner at return cls.owner.x + y + 1.
The line setattr(owner, name, self.inner), breaks the descriptor because owner.name => Outer.A => A is no longer an instance of the class inner.
Hope this helps.
class inner:
def __init__(self, inner):
self.inner = inner
def __get__(self, instance, owner):
print('__get__ method executed, only once... ')
name = self.inner.__name__
setattr(self.inner, 'owner', owner)
setattr(owner, name, self.inner) # breaks descriptor
return self.inner #returns Inner
class Outer:
x = 1
#inner
class A:
#classmethod
def add(cls, y=3):
return cls.owner.x + y + 1
print(Outer.A.add(0)) # First time executes inner.__get__ method
print(Outer.A.add(0)) # Second time not necessary.
>> __get__ method executed, only once...
>> 2
>> 2
It can be done by parsing the outer class object into inner class.
class Outer():
def __init__(self,userinput):
self.userinput = userinput
def outer_function(self):
self.a = self.userinput + 2
class Inner():
def inner_function(self):
self.b = self.a + 10
after defining this, it need to run the function
m = Outer(3)
m.outer_function()
print (m.a)
#this will output 5
Now it has the variable of outer class.
and then, it need to run inner class functions.
m.Inner.inner_function(m)
The object m of outer class is parsed into the function of inner class (inside the brackets)
Now, the inner class function is accessing self.a from the outer class.
print (m.b)
#this will output 15
It is too simple:
Input:
class A:
def __init__(self):
pass
def func1(self):
print('class A func1')
class B:
def __init__(self):
a1 = A()
a1.func1()
def func1(self):
print('class B func1')
b = A.B()
b.func1()
Output
class A func1
class B func1
I have a question which is more regarding OOP in general rather than python specific.
Is ist possible to store instances of ClassA in instance of ClassB without a specific method, i.e. by some kind of inheritance.
Example: let's say I have one Model class and one Variable class
class Model():
def __init__(self):
self.vars = []
def _update_vars(self,Variable):
self.vars.append(Variable)
class Variable(Model):
def __init__(self,**kwargs):
self.__dict__.update(kwargs)
Is it now possible to call _update_vars whenever an instance of variable is being created.
So if I do something like this:
mdl = Model()
varA = Variable(...)
varB = Variable(...)
that mdl.vars would now include varA and varB.
I know that I could easily do this by passing the variables as an argument to a "public" method of Model. So I am not looking for
mdl.update_vars(varA)
So my two questions are:
is this possible?
if yes: would this very non-standard OOP programming?
Thanks for your help!
That's not how class inheritance is supposed to work. You only want to inherit something if the child class is going to make use of a good amount of the attributes/methods within the parent class. If the child class has a markedly different structure it should be a class of its own.
In either case, as mentioned by #jasonharper, at some point you would need to give direction as to which Variable instance belongs in which Model instance, so you're likely to end up with something like these:
varA = Variable(mdl, ...)
# or this
mdl.varA = Variable(...)
With the first way, you would maintain the method on your Variable class:
class Foo:
def __init__(self):
self.vars = []
class Bar:
def __init__(self, foo_instance, **kwargs):
foo_instance.vars.append(self)
f = Foo()
b = Bar(f, hello='hey')
f.vars
# [<__main__.Bar object at 0x03F6B4B0>]
With the second way, you can append the Variable instances into a list each time it's added:
class Foo:
def __init__(self):
self.vars = []
def __setattr__(self, name, val):
self.__dict__.update({name: val})
if not name == 'vars': # to prevent a recursive loop
self.vars.append(val)
f = Foo()
f.vars
# []
f.a = 'bar'
f.vars
# ['bar']
Of course, an easier way would be to just look directly into the __dict__ each time you want vars:
class Bar:
#property
def vars(self):
# Or you can return .items() if you want both the name and the value
return list(self.__dict__.values())
b = Bar()
b.a = 'hello'
b.vars
# ['hello']
Both of these will work the same even if you assigned the attributes with your own class instances.
You can use super() for this and pass the instance to the parent
class Model():
vars = []
def __init__(self, other=None):
if other:
self.vars.append(other)
class Variable(Model):
def __init__(self, a):
self.a = a
super().__init__(self)
mdl = Model()
varA = Variable(3)
varB = Variable(4)
print(mdl.vars)
I am trying to create a new MyClass instance in MyClass's definition.
Why does this code fail and how can achieve it?
class MyClass:
def __init__(self):
self.child=MyClass()
mc=MyClass()
Well, it fails because it has infinite recursion. Think about it, if every MyClass has a child which is a MyClass, it will go on for infinity!
You can resolve this a couple of ways. First, you can have a parameter to the constructor:
class MyClass:
def __init__(self, create = True):
if create:
self.child = MyClass(False)
mc = MyClass()
Or, you can have another, external method:
class MyClass:
def set_child(self,child = None):
# I prefer to make child optional for ease of use.
child = MyClass() if child is None else child
self.child=child
mc=MyClass()
mc.set_child()
I personally prefer the first solution as it means that outside objects don't need to know anything about the class. Of course, you could combine the two:
class MyClass:
def __init__(self, create):
if create:
self.set_child(create=False)
def set_child(self,child = None, create = True):
child = MyClass(create) if child is None else child
self.child=child
mc=MyClass()
This way mc has a child by default and you have the option of setting the child whenever you like.
Then there is also the "let's create a certain number" approach:
class MyClass:
def __init__(self, count = 10):
count -= 1
if count:
# the first child gets the value 9.
# the second gets 8.
# when the count gets to 0, stop!
self.child = MyClass(count)
Aside: If you want to get an object's class, you can use the value obj.__class__. That will output MyClass in all of the examples above.
You're making an infinitely recursing call — MyClass is creating another MyClass during initialization, and thus it recurses infinitely.
You may want to do something like:
class MyClass:
def create_child(self):
self.child=MyClass()
mc=MyClass()
mc.create_child()
If you're feeling particularly naughty, you could try:
class MyClass(object):
#property
def child(self):
if self._child is None: self._child = MyClass()
return self._child
def __init__(self):
self._child=None
mc=MyClass()
What you did there is actualy recursive, the new isntance of MyClass will create a new instance that will in turn create a new one, etc ...
Soo I supose that is why your code fails, I can't tell for sure since you didn't post the error message.
I suggest to define two classes:
class MyClass(object):
def __init__(self):
self.child = MyChildClass()
...many other methods...
class MyChildClass(MyClass):
def __init__(self):
pass
I think that if two classes must behave in two different ways, they must be different (although one can subclass the other)
I have a situation like so...
class Outer(object):
def some_method(self):
# do something
class Inner(object):
def __init__(self):
self.Outer.some_method() # <-- this is the line in question
How can I access the Outer class's method from the Inner class?
You're trying to access Outer's class instance, from inner class instance. So just use factory-method to build Inner instance and pass Outer instance to it.
class Outer(object):
def createInner(self):
return Outer.Inner(self)
class Inner(object):
def __init__(self, outer_instance):
self.outer_instance = outer_instance
self.outer_instance.somemethod()
def inner_method(self):
self.outer_instance.anothermethod()
The methods of a nested class cannot directly access the instance attributes of the outer class.
Note that it is not necessarily the case that an instance of the outer class exists even when you have created an instance of the inner class.
In fact, it is often recommended against using nested classes, since the nesting does not imply any particular relationship between the inner and outer classes.
maybe I'm mad but this seems very easy indeed - the thing is to make your inner class inside a method of the outer class...
def do_sthg(self):
...
def mess_around(self):
outer_class_self = self
class Mooble():
def do_sthg_different(self):
...
outer_class_self.do_sthg()
Plus... "self" is only used by convention, so you could do this:
def do_sthg(self):
...
def mess_around(outer_class_self):
class Mooble():
def do_sthg_different(self):
...
outer_class_self.do_sthg()
It might be objected that you can't then create this inner class from outside the outer class... but this ain't true:
class Bumblebee():
def do_sthg(self):
print "sthg"
def give_me_an_inner_class(outer_class_self):
class Mooble():
def do_sthg_different(self):
print "something diff\n"
outer_class_self.do_sthg()
return Mooble
then, somewhere miles away:
blob = Bumblebee().give_me_an_inner_class()()
blob.do_sthg_different()
even push the boat out a bit and extend this inner class (NB to get super() to work you have to change the class signature of Mooble to class Mooble(object)).
class InnerBumblebeeWithAddedBounce(Bumblebee().give_me_an_inner_class()):
def bounce(self):
print "bounce"
def do_sthg_different(self):
super(InnerBumblebeeWithAddedBounce, self).do_sthg_different()
print "and more different"
ibwab = InnerBumblebeeWithAddedBounce()
ibwab.bounce()
ibwab.do_sthg_different()
later
mrh1997 raised an interesting point about the non-common inheritance of inner classes delivered using this technique. But it seems that the solution is pretty straightforward:
class Fatty():
def do_sthg(self):
pass
class InnerFatty(object):
pass
def give_me_an_inner_fatty_class(self):
class ExtendedInnerFatty(Fatty.InnerFatty):
pass
return ExtendedInnerFatty
fatty1 = Fatty()
fatty2 = Fatty()
innerFattyClass1 = fatty1.give_me_an_inner_fatty_class()
innerFattyClass2 = fatty2.give_me_an_inner_fatty_class()
print (issubclass(innerFattyClass1, Fatty.InnerFatty))
print (issubclass(innerFattyClass2, Fatty.InnerFatty))
I found this.
Tweaked to suite your question:
class Outer(object):
def some_method(self):
# do something
class _Inner(object):
def __init__(self, outer):
outer.some_method()
def Inner(self):
return _Inner(self)
I’m sure you can somehow write a decorator for this or something
related: What is the purpose of python's inner classes?
A few years late to the party.... but to expand on #mike rodent's wonderful answer, I've provided my own example below that shows just how flexible his solution is, and why it should be (or should have been) the accepted answer.
Python 3.7
class Parent():
def __init__(self, name):
self.name = name
self.children = []
class Inner(object):
pass
def Child(self, name):
parent = self
class Child(Parent.Inner):
def __init__(self, name):
self.name = name
self.parent = parent
parent.children.append(self)
return Child(name)
parent = Parent('Bar')
child1 = parent.Child('Foo')
child2 = parent.Child('World')
print(
# Getting its first childs name
child1.name, # From itself
parent.children[0].name, # From its parent
# Also works with the second child
child2.name,
parent.children[1].name,
# Go nuts if you want
child2.parent.children[0].name,
child1.parent.children[1].name
)
print(
# Getting the parents name
parent.name, # From itself
child1.parent.name, # From its children
child2.parent.name,
# Go nuts again if you want
parent.children[0].parent.name,
parent.children[1].parent.name,
# Or insane
child2.parent.children[0].parent.children[1].parent.name,
child1.parent.children[1].parent.children[0].parent.name
)
# Second parent? No problem
parent2 = Parent('John')
child3 = parent2.Child('Doe')
child4 = parent2.Child('Appleseed')
print(
child3.name, parent2.children[0].name,
child4.name, parent2.children[1].name,
parent2.name # ....
)
Output:
Foo Foo World World Foo World
Bar Bar Bar Bar Bar Bar Bar
Doe Doe Appleseed Appleseed John
Again, a wonderful answer, props to you mike!
You can easily access to outer class using metaclass: after creation of outer class check it's attribute dict for any classes (or apply any logic you need - mine is just trivial example) and set corresponding values:
import six
import inspect
# helper method from `peewee` project to add metaclass
_METACLASS_ = '_metaclass_helper_'
def with_metaclass(meta, base=object):
return meta(_METACLASS_, (base,), {})
class OuterMeta(type):
def __new__(mcs, name, parents, dct):
cls = super(OuterMeta, mcs).__new__(mcs, name, parents, dct)
for klass in dct.values():
if inspect.isclass(klass):
print("Setting outer of '%s' to '%s'" % (klass, cls))
klass.outer = cls
return cls
# #six.add_metaclass(OuterMeta) -- this is alternative to `with_metaclass`
class Outer(with_metaclass(OuterMeta)):
def foo(self):
return "I'm outer class!"
class Inner(object):
outer = None # <-- by default it's None
def bar(self):
return "I'm inner class"
print(Outer.Inner.outer)
>>> <class '__main__.Outer'>
assert isinstance(Outer.Inner.outer(), Outer)
print(Outer().foo())
>>> I'm outer class!
print(Outer.Inner.outer().foo())
>>> I'm outer class!
print(Outer.Inner().outer().foo())
>>> I'm outer class!
print(Outer.Inner().bar())
>>> I'm inner class!
Using this approach, you can easily bind and refer two classes between each other.
I've created some Python code to use an outer class from its inner class, based on a good idea from another answer for this question. I think it's short, simple and easy to understand.
class higher_level__unknown_irrelevant_name__class:
def __init__(self, ...args...):
...other code...
# Important lines to access sub-classes.
subclasses = self._subclass_container()
self.some_subclass = subclasses["some_subclass"]
del subclasses # Free up variable for other use.
def sub_function(self, ...args...):
...other code...
def _subclass_container(self):
_parent_class = self # Create access to parent class.
class some_subclass:
def __init__(self):
self._parent_class = _parent_class # Easy access from self.
# Optional line, clears variable space, but SHOULD NOT BE USED
# IF THERE ARE MULTIPLE SUBCLASSES as would stop their parent access.
# del _parent_class
class subclass_2:
def __init__(self):
self._parent_class = _parent_class
# Return reference(s) to the subclass(es).
return {"some_subclass": some_subclass, "subclass_2": subclass_2}
The main code, "production ready" (without comments, etc.). Remember to replace all of each value in angle brackets (e.g. <x>) with the desired value.
class <higher_level_class>:
def __init__(self):
subclasses = self._subclass_container()
self.<sub_class> = subclasses[<sub_class, type string>]
del subclasses
def _subclass_container(self):
_parent_class = self
class <sub_class>:
def __init__(self):
self._parent_class = _parent_class
return {<sub_class, type string>: <sub_class>}
Explanation of how this method works (the basic steps):
Create a function named _subclass_container to act as a wrapper to access the variable self, a reference to the higher level class (from code running inside the function).
Create a variable named _parent_class which is a reference to the variable self of this function, that the sub-classes of _subclass_container can access (avoids name conflicts with other self variables in subclasses).
Return the sub-class/sub-classes as a dictionary/list so code calling the _subclass_container function can access the sub-classes inside.
In the __init__ function inside the higher level class (or wherever else needed), receive the returned sub-classes from the function _subclass_container into the variable subclasses.
Assign sub-classes stored in the subclasses variable to attributes of the higher level class.
A few tips to make scenarios easier:
Making the code to assign the sub classes to the higher level class easier to copy and be used in classes derived from the higher level class that have their __init__ function changed:
Insert before line 12 in the main code:
def _subclass_init(self):
Then insert into this function lines 5-6 (of the main code) and replace lines 4-7 with the following code:
self._subclass_init(self)
Making subclass assigning to the higher level class possible when there are many/unknown quantities of subclasses.
Replace line 6 with the following code:
for subclass_name in list(subclasses.keys()):
setattr(self, subclass_name, subclasses[subclass_name])
Example scenario of where this solution would be useful and where the higher level class name should be impossible to get:
A class, named "a" (class a:) is created. It has subclasses that need to access it (the parent). One subclass is called "x1". In this subclass, the code a.run_func() is run.
Then another class, named "b" is created, derived from class "a" (class b(a):). After that, some code runs b.x1() (calling the sub function "x1" of b, a derived sub-class). This function runs a.run_func(), calling the function "run_func" of class "a", not the function "run_func" of its parent, "b" (as it should), because the function which was defined in class "a" is set to refer to the function of class "a", as that was its parent.
This would cause problems (e.g. if function a.run_func has been deleted) and the only solution without rewriting the code in class a.x1 would be to redefine the sub-class x1 with updated code for all classes derived from class "a" which would obviously be difficult and not worth it.
Do you mean to use inheritance, rather than nesting classes like this? What you're doing doesn't make a heap of sense in Python.
You can access the Outer's some_method by just referencing Outer.some_method within the inner class's methods, but it's not going to work as you expect it will. For example, if you try this:
class Outer(object):
def some_method(self):
# do something
class Inner(object):
def __init__(self):
Outer.some_method()
...you'll get a TypeError when initialising an Inner object, because Outer.some_method expects to receive an Outer instance as its first argument. (In the example above, you're basically trying to call some_method as a class method of Outer.)
Another possibility:
class _Outer (object):
# Define your static methods here, e.g.
#staticmethod
def subclassRef ():
return Outer
class Outer (_Outer):
class Inner (object):
def outer (self):
return _Outer
def doSomething (self):
outer = self.outer ()
# Call your static mehthods.
cls = outer.subclassRef ()
return cls ()
What we can do is pass the self variable of Outer Class inside the Inner Class as Class Argument and Under Outer init initialise the Inner Class with Outer self passed into Inner
class Outer:
def __init__(self):
self.somevalue=91
self.Inner=self.Inner(self)
def SomeMethod(self):
print('This is Something from Outer Class')
class Inner:
def __init__(self,Outer)
self.SomeMethod=Outer.SomeMethod
self.somevalue=Outer.somevalue
def SomeAnotherMethod(self):
print(self.somevalue)
self.SomeMethod()
>>>f=Outer()
>>>f.Inner.SomeAnotherMethod()
91
This is Something from Outer Class
Now After running this function it Works
Expanding on #tsnorri's cogent thinking, that the outer method may be a static method:
class Outer(object):
#staticmethod
def some_static_method(self):
# do something
class Inner(object):
def __init__(self):
self.some_static_method() # <-- this will work later
Inner.some_static_method = some_static_method
Now the line in question should work by the time it is actually called.
The last line in the above code gives the Inner class a static method that's a clone of the Outer static method.
This takes advantage of two Python features, that functions are objects, and scope is textual.
Usually, the local scope references the local names of the (textually) current function.
...or current class in our case. So objects "local" to the definition of the Outer class (Inner and some_static_method) may be referred to directly within that definition.
You may create a class, to decorate inner classes. In this case #inner.
Since this a decorator: Outer.A = inner(Outer.A). Once your code requires Outer.A it will be executed inner.__get__ method, which returns the original class (A) with a new attribute set on it: A.owner = Outer.
A classmethod in class A, in this case def add(cls, y=3), may use new attribute owner at return cls.owner.x + y + 1.
The line setattr(owner, name, self.inner), breaks the descriptor because owner.name => Outer.A => A is no longer an instance of the class inner.
Hope this helps.
class inner:
def __init__(self, inner):
self.inner = inner
def __get__(self, instance, owner):
print('__get__ method executed, only once... ')
name = self.inner.__name__
setattr(self.inner, 'owner', owner)
setattr(owner, name, self.inner) # breaks descriptor
return self.inner #returns Inner
class Outer:
x = 1
#inner
class A:
#classmethod
def add(cls, y=3):
return cls.owner.x + y + 1
print(Outer.A.add(0)) # First time executes inner.__get__ method
print(Outer.A.add(0)) # Second time not necessary.
>> __get__ method executed, only once...
>> 2
>> 2
It can be done by parsing the outer class object into inner class.
class Outer():
def __init__(self,userinput):
self.userinput = userinput
def outer_function(self):
self.a = self.userinput + 2
class Inner():
def inner_function(self):
self.b = self.a + 10
after defining this, it need to run the function
m = Outer(3)
m.outer_function()
print (m.a)
#this will output 5
Now it has the variable of outer class.
and then, it need to run inner class functions.
m.Inner.inner_function(m)
The object m of outer class is parsed into the function of inner class (inside the brackets)
Now, the inner class function is accessing self.a from the outer class.
print (m.b)
#this will output 15
It is too simple:
Input:
class A:
def __init__(self):
pass
def func1(self):
print('class A func1')
class B:
def __init__(self):
a1 = A()
a1.func1()
def func1(self):
print('class B func1')
b = A.B()
b.func1()
Output
class A func1
class B func1