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 am trying to write a function taking a string as an argument and using this argument as a class object.
Note that my explanantion might be strangely formulated sice I could not find an answer online. The MWE below should clarify what I mean, the problematic line is indicated.
Edit: in the MWE, "print" is an example. I need to be able to call the object to update it, print it or, in the case of a list, append to it. I need access to the object itself, not the value of the object.
MWE
# Create a class
class myClass():
def __init__(self):
self.one = "Test"
self.two = "Plop"
# Define function
def myFunction (parameter):
print(myObject.parameter)##### This line is currently not possible.
# Use class
myObject = myClass()
# Use function
myFunction("one")
I am not trying to append a new object to the class, only to call an existing object.
Is this even possible?
Looks like you need the built-in function called getattr
my_object = myClass()
def my_function(parameter):
print(getattr(my_object, parameter, None))
also this is not the best practice to call objects from outer scope like that. i'd suggest to use dict magic methods:
class MyClass:
def __init__(self):
self.one = "Test"
self.two = "Plop"
def __getitem__(self, parameter):
return getattr(self, parameter, None)
def __setitem__(self, parameter, value):
return setattr(self, parameter, value)
my_obj = MyClass()
parameter = "x"
print(my_obj[parameter])
my_obj[parameter] = "test"
print(my_obj.x)
You need to use getarttr():
# Create a class
class myClass():
def __init__(self):
self.one = "Test"
self.two = "Plop"
# Use class
myObject = myClass()
# Define function
def myFunction(parameter):
print(getattr(myObject, parameter))##### This line is currently possible.
# Use function
myFunction("one")
Question is at the end
What am I trying to do is :
Inject property to created object and set it instead of a variable (success)
Inject method (let's call it METHOD) to created object, object had no such method before (success)
Call public another method from property using self (success)
Call METHOD from property using self (success)
Get private class variable from METHOD using self (failure)
Now, here is some code:
from types import MethodType
def add_property(instance, name, method):
cls = type(instance)
cls = type(cls.__name__, (cls,), {})
cls.__perinstance = True
instance.__class__ = cls
setattr(cls, name, property(method))
def add_variable(instance, name, init_value = 0 ):
setattr(type(instance), name, init_value)
class Simulation:
def __init__(self):
self.finished = False
self.__hidden = -10
def someloop(self):
while not self.finished:
self.__private_method()
def __private_method(self):
pass
def public_method(self):
pass
def mocked_method(self):
print(type(self))
print(self.__dict__)
print(self.__hidden)
def finished(self):
print("Execute finished",type(self))
self.public_method()
self.mocked_update()
return True
simulation = Simulation()
add_property(simulation, "finished", finished)
add_variable(simulation, "count_finished", 0)
simulation.mocked_update = MethodType(mocked_method, simulation)
simulation.someloop()
What code produced (those prints):
Execute finished '<class '__main__.Simulation'>
<class '__main__.Simulation'>
{'finished': False, '_Simulation__hidden': -10, 'mocked_update': <bound method mocked_method of <__main__.Simulation object at 0x030D2F10>>}
(...)
AttributeError: 'Simulation' object has no attribute '__hidden'
As you can see self is what it should be (simulation class), it was properly injected and yet it doesn't work.
In case you are wondering :
print(self._Simulation__hidden)
obviously works inside mocked_update.
Hence my question : Is there any chance for me to access this variable using self?
Motivation
Since there was a question in the comments section:
This does not serve any real purpose, it is just an experiment.
The name mangling of "private" members is strictly done within class definitions. To achieve the desired purpose, which is to have self.__hidden translated to self._Simulation_hidden you need simply define it within an appropriately named class.
For example:
def make_mocked_method():
class Simulation:
# this is your code, but now its inside a class stanza so '__' will be mangled
def mocked_method(self):
print(type(self))
print(self.__dict__)
print(self.__hidden)
return Simulation.mocked_method
Now mocked_method will access the desired attribute correctly:
simulation.mocked_update = MethodType(make_mocked_method(), simulation)
simulation.someloop()
gives:
<class '__main__.Simulation'>
{'finished': False, 'mocked_update': <bound method make_mocked_method.<locals>.Simulation.mocked_method of <__main__.Simulation object at 0x101c00a58>>, '_Simulation__hidden': -10}
-10
Extension
This relies on us hard coding the name of the class we're adding the method to (Simulation). To avoid that we can instead use an exec:
def make_mocked_method(cls):
txt = """class {}:
def mocked_method(self):
print(type(self))
print(self.__dict__)
print(self.__hidden)
""".format(cls.__name__)
ns = {}
exec(txt, ns)
return ns[cls.__name__].mocked_method
Unfortunately here the function we wish to add must be defined as text, it can't be some already defined arbitrary function object. (That might possibly be solved by using inspect to find its source and then recompiling that source within a class stanza using exec (and judicious choice of globals).
I have a class that I want to take an arbitrary method at initialization to use for string parsing depending on the context.
Using a method defined outside of a class as discussed here: Python define method outside of class definition?
def my_string_method(self):
return self.var.strip()
class My_Class():
def __init__(self, string_method):
self.var = ' foo '
self.string_method = string_method
def use_string_method(self):
return self.string_method()
instance = My_Class(string_method=my_string_method)
print instance.use_string_method()
I get the error "TypeError: use_string_method() takes exactly 1 argument (0 given)".
Shouldn't the self argument be passed implicitly to use_string_method?
Is there a way to define the function such that this occurs, or do I need to explicitly pass the self argument to methods defined outside of the class as such:
class My_Class():
def __init__(self, string_method):
self.var = ' foo '
self.string_method = string_method
def use_string_method(self):
return self.string_method(self)
You will have to wrap the passed in function in "MethodType".
From within your init:
self.string_method = types.MethodType(string_method, self)
This binds the method to the class and allows it to receive the implicit self parameter. Make sure you import types at the top of your script.
i have the following class which i use when declaring 'constants' to map one value to another. Is there away in python implement a default method such that anytime an instance of this class referenced without a specific method, a default method is executed?
class FieldMap:
def __init__(self, old_field, new_field):
self._fld_map = (old_field, new_field)
def old_fld(self):
return self._fld_map[0]
def new_fld(self):
return self._fld_map[1]
SEC_ID = FieldMap('value','price')
SEC_NAME = FieldMap('entity_name', 'security_name')
SEC_TICKER = FieldMap('entity_attr', 'ticker')
#Edit: updating example to provide a real example of what i want to achieve
dict = {}
dict['price'] = 1234
print dict[SEC_ID] <--would like this to print out the value 1234 because ideally, the default method would call new_fld() and return 'price'
It doesn't call a default method, but it sounds like you just want to override __str__:
def __str__(self):
return self._fld_map[1]
Note that this is just the definition of new_fld, so you could simply add the following to your class:
__str__ = new_fld
There's no way to implement an automatic method call in all cases, but it is possible to hook into certain method calls. In the case of print, Python will attempt to call a __str__ method on the instance if one exists. So you could do something like this:
class FieldMap:
def __init__(self, old_field, new_field):
self._fld_map = (old_field, new_field)
def old_fld(self):
return self._fld_map[0]
def new_fld(self):
return self._fld_map[1]
def __str__(self):
return self.new_fld()