Related
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 would like to know if it's possible, and if yes, how to access attribute(s) of a "super" class instance, when having composition implemented.
Example provided below is only to provide idea here and setup common ground on further explanations.
I want to have access to "id" attribute for an instance of MiniVan directly from object "door" (type DoorElement).
My Code
class Car:
def __init__(self, _id):
self.id = _id
class CarElement:
def __init__(self, name):
self.name = name
def get_car_id(self):
# Body which will access value of attribute "id"
return car_id
class MiniVan(Car):
def __init__(self, _id):
super(MiniVan, self).__init__(_id)
self.door = DoorElement('door')
self.engine = EngineElement('engine')
class DoorElement(CarElement):
def __init__(self, name):
super(DoorElement, self).__init__(name)
class EngineElement(CarElement):
def __init__(self, name):
super(EngineElement, self).__init__(name)
def main():
mini_van = MiniVan(123)
id_from_door = mini_van.door.get_car_id()
id_from_engine = mini_van.engine.get_car_id()
print(id_from_door) # Expected output 123
print(id_from_engine) # Expected output 123
if __name__ == '__main__':
main()
Expected:
Printed out twice "123"
What I've tried:
Passing required attribute during creating object
I know that I could just define init method with passing "car_id" but for some reasons I would love to avoid it if possible. If not, I would propably just go for it.
to set class attribute, and then call it from CarElement class within classmethod e.g.:
#classmethod
def get_id(cls):
return Car.id
But issue with this solution is that, I can have many child-classes for Car class (MiniVan, Truck, etc.) and I want have it still working.
Trying to use descriptor
def __get__(self, instance, owner):
return instance.id
But I could understand it wrong, and actually getter (as far as I understand clean code) should return instance of a class and not any attribute.
Additional Info
I will ALWAYS use CarElement (or child classes) instances as attributes of instance of Car (or child classes) instances - different usage will be treated as use-error
There can be a lot of different child classes of Car class, but always within inheritance way ( Car <- RacingCar(Car) <- FormulaOneCar(RacingCar) ) but no composition
In order for your code to work, you would have to initialize all CarElement-s with car_id. Currently, the error you are getting comes from lack of such a variable in the scope of the method. My idea of a change is this:
class CarElement:
def __init__(self, name, car_id):
self.name = name
self.car_id = car_id
def get_car_id(self):
# Body which will access value of attribute id
return self.car_id
I can't see any other magic way.
I am using python 3.4 and i am new in object oriented programming and want to access the parent class member in my child class. But it is not accessible. Can anyone help me to get rid of this?
# Base class members can be accessed in
# derived class using base class name.
# Parent or super class
class Company:
def BasicInfo(self):
self.CompanyName = "ABC Solutions"
self.Address = "XYZ"
# Inherited or child class
class Employee(Company):
# constructor
def __init__(self, Name):
print("Employee Name:", Name)
print("Company Name:", self.CompanyName)
def main():
# Create an object
emp01 = Employee("John")
if __name__ == "__main__":
main()
The below mentioned code is working but using the same concept, my code is not working, why? Can anyone explain me the reason.
class Room:
def __init__(self):
self.roomno = 0
self.rcap = 0
self.rooms = {}
self.nog = 10
def addRoom(self):
self.rcap = input("Please enter room capacity:\n")
self.rooms[self.roomno] = self.rcap
class Booking(Room):
def addBooking(self):
while int(self.nog) > int(self.rcap):
print("Guest count exceeds room capacity of: %d" % int(self.rcap))
x = Booking()
x.addRoom()
x.addBooking()
You're missing a call to the superclass' BasicInfo method:
def __init__(self, Name):
print("Employee Name:", Name)
super().BasicInfo()
# ^^Here^^
print("Company Name:", self.CompanyName)
You can replace super().BasicInfo() with a direct reference to the class obviously:
Company.BasicInfo(self)
In your second example, the subclass does not define a __init__ method, so it would inherit that from parent; as a result, the instance variables would be present in the child class.
Your base class method BasicInfo is never getting called. If you call it explicitly either in your child class's __init__, it would work
class Employee(Company):
# constructor
def __init__(self, Name):
super(Employee, self).BasicInfo()
print("Employee Name:", Name)
print("Company Name:", self.CompanyName)
I'm playing around with OOP in Python and I am trying to figure out some stuff related to inheritance. . I have some code here that has a few classes. A class called Blacksmith which behaves as expected and a class called Hero which I am trying to call a function from but I recieve an unexpected output.
class Character(object):
def __init__(self,name):
self.health=100
self.name = name
# self.player = player
def printName(self):
print self.name
#def printPlayerName(self):
# print self.player
class Blacksmith(Character):
def __init__(self,name, forgeName):
super(Blacksmith, self).__init__(name)
#self.name = "Billy"
self.forge = Forge(forgeName)
class Hero(Character):
playerName = "Player"
def __init__(self,name):
super(Hero, self).__init__(name)
def setplayername(self,inputplayername):
playerName = inputplayername
class Forge:
def __init__(self,forgeName):
self.name = forgeName
bs = Blacksmith("Billy", "Billy's Forge")
print bs.health
bs.printName()
print bs.forge.name
player1 = Hero("Methos")
print player1.name
player1.setplayername("Chris")
#print playher1.playerName
print player1.playerName
Output is:
raina#DESKTOP-291MTC0 ~/python
$ python learningoopclasses01.py
100
Billy
Billy's Forge
Methos
Player
Can anyone explain why this output says "Player" and not "Chris". Another question I have is I am not entirely sure how the init methods work. What does super do in these cases? What does calling init with a name value do exactly? Thanks.
__init__ is called when an object of that Class is created. With this method, we will also use the self variable to represent the instance of the object itself. It has to be explicitly declared in Python to be defined on an object.
For example,
class Student():
def __init__(self, score1, score2, score3):
self.scores = [score1, score2, score3]
If you want to assign scores to Student 1, you would only need to use because stu_1 already has score as an attribute in it:
stu_1 = Student(80, 90, 85)
In addition, __init__ also will notify you if any parameters are entered incorrectly according to what it has been set up.
super() is used to first call the parent(super) class of Blacksmith, which is Character, and allows you access Character's property.
The call to super() in Blacksmith's __init__ method is equal to its superclass, which in this case is Character.
You could also replace super(Blacksmith, self).__init__(name) with Character.__init__(self, name). The two are equivalent.
A slight adjustment to
def setplayername(self,inputplayername):
self.playerName = inputplayername
In the Hero class will fix it, if you don't want to change anything else.
I would like to replace an object instance by another instance inside a method like this:
class A:
def method1(self):
self = func(self)
The object is retrieved from a database.
It is unlikely that replacing the 'self' variable will accomplish whatever you're trying to do, that couldn't just be accomplished by storing the result of func(self) in a different variable. 'self' is effectively a local variable only defined for the duration of the method call, used to pass in the instance of the class which is being operated upon. Replacing self will not actually replace references to the original instance of the class held by other objects, nor will it create a lasting reference to the new instance which was assigned to it.
As far as I understand, If you are trying to replace the current object with another object of same type (assuming func won't change the object type) from an member function. I think this will achieve that:
class A:
def method1(self):
newObj = func(self)
self.__dict__.update(newObj.__dict__)
It is not a direct answer to the question, but in the posts below there's a solution for what amirouche tried to do:
Python object conversion
Can I dynamically convert an instance of one class to another?
And here's working code sample (Python 3.2.5).
class Men:
def __init__(self, name):
self.name = name
def who_are_you(self):
print("I'm a men! My name is " + self.name)
def cast_to(self, sex, name):
self.__class__ = sex
self.name = name
def method_unique_to_men(self):
print('I made The Matrix')
class Women:
def __init__(self, name):
self.name = name
def who_are_you(self):
print("I'm a women! My name is " + self.name)
def cast_to(self, sex, name):
self.__class__ = sex
self.name = name
def method_unique_to_women(self):
print('I made Cloud Atlas')
men = Men('Larry')
men.who_are_you()
#>>> I'm a men! My name is Larry
men.method_unique_to_men()
#>>> I made The Matrix
men.cast_to(Women, 'Lana')
men.who_are_you()
#>>> I'm a women! My name is Lana
men.method_unique_to_women()
#>>> I made Cloud Atlas
Note the self.__class__ and not self.__class__.__name__. I.e. this technique not only replaces class name, but actually converts an instance of a class (at least both of them have same id()). Also, 1) I don't know whether it is "safe to replace a self object by another object of the same type in [an object own] method"; 2) it works with different types of objects, not only with ones that are of the same type; 3) it works not exactly like amirouche wanted: you can't init class like Class(args), only Class() (I'm not a pro and can't answer why it's like this).
Yes, all that will happen is that you won't be able to reference the current instance of your class A (unless you set another variable to self before you change it.) I wouldn't recommend it though, it makes for less readable code.
Note that you're only changing a variable, just like any other. Doing self = 123 is the same as doing abc = 123. self is only a reference to the current instance within the method. You can't change your instance by setting self.
What func(self) should do is to change the variables of your instance:
def func(obj):
obj.var_a = 123
obj.var_b = 'abc'
Then do this:
class A:
def method1(self):
func(self) # No need to assign self here
In many cases, a good way to achieve what you want is to call __init__ again. For example:
class MyList(list):
def trim(self,n):
self.__init__(self[:-n])
x = MyList([1,2,3,4])
x.trim(2)
assert type(x) == MyList
assert x == [1,2]
Note that this comes with a few assumptions such as the all that you want to change about the object being set in __init__. Also beware that this could cause problems with inheriting classes that redefine __init__ in an incompatible manner.
Yes, there is nothing wrong with this. Haters gonna hate. (Looking at you Pycharm with your in most cases imaginable, there's no point in such reassignment and it indicates an error).
A situation where you could do this is:
some_method(self, ...):
...
if(some_condition):
self = self.some_other_method()
...
return ...
Sure, you could start the method body by reassigning self to some other variable, but if you wouldn't normally do that with other parametres, why do it with self?
One can use the self assignment in a method, to change the class of instance to a derived class.
Of course one could assign it to a new object, but then the use of the new object ripples through the rest of code in the method. Reassiging it to self, leaves the rest of the method untouched.
class aclass:
def methodA(self):
...
if condition:
self = replace_by_derived(self)
# self is now referencing to an instance of a derived class
# with probably the same values for its data attributes
# all code here remains untouched
...
self.methodB() # calls the methodB of derivedclass is condition is True
...
def methodB(self):
# methodB of class aclass
...
class derivedclass(aclass):
def methodB(self):
#methodB of class derivedclass
...
But apart from such a special use case, I don't see any advantages to replace self.
You can make the instance a singleton element of the class
and mark the methods with #classmethod.
from enum import IntEnum
from collections import namedtuple
class kind(IntEnum):
circle = 1
square = 2
def attr(y): return [getattr(y, x) for x in 'k l b u r'.split()]
class Shape(namedtuple('Shape', 'k,l,b,u,r')):
self = None
#classmethod
def __repr__(cls):
return "<Shape({},{},{},{},{}) object at {}>".format(
*(attr(cls.self)+[id(cls.self)]))
#classmethod
def transform(cls, func):
cls.self = cls.self._replace(**func(cls.self))
Shape.self = Shape(k=1, l=2, b=3, u=4, r=5)
s = Shape.self
def nextkind(self):
return {'k': self.k+1}
print(repr(s)) # <Shape(1,2,3,4,5) object at 139766656561792>
s.transform(nextkind)
print(repr(s)) # <Shape(2,2,3,4,5) object at 139766656561888>