We Keep Coding

How to overwrite self after reading yaml? [duplicate]

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>

Access attribute of outer class from nested class [duplicate]

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

Python unittest.main() unable to instantiate inner classes [duplicate]

I'm trying to understand scope in nested classes in Python. Here is my example code:
class OuterClass:
outer_var = 1
class InnerClass:
inner_var = outer_var
The creation of class does not complete and I get the error:
<type 'exceptions.NameError'>: name 'outer_var' is not defined
Trying inner_var = Outerclass.outer_var doesn't work.
I get:
<type 'exceptions.NameError'>: name 'OuterClass' is not defined
I am trying to access the static outer_var from InnerClass.
Is there a way to do this?

class Outer(object):
outer_var = 1
class Inner(object):
#property
def inner_var(self):
return Outer.outer_var
This isn't quite the same as similar things work in other languages, and uses global lookup instead of scoping the access to outer_var. (If you change what object the name Outer is bound to, then this code will use that object the next time it is executed.)
If you instead want all Inner objects to have a reference to an Outer because outer_var is really an instance attribute:
class Outer(object):
def __init__(self):
self.outer_var = 1
def get_inner(self):
return self.Inner(self)
# "self.Inner" is because Inner is a class attribute of this class
# "Outer.Inner" would also work, or move Inner to global scope
# and then just use "Inner"
class Inner(object):
def __init__(self, outer):
self.outer = outer
#property
def inner_var(self):
return self.outer.outer_var
Note that nesting classes is somewhat uncommon in Python, and doesn't automatically imply any sort of special relationship between the classes. You're better off not nesting. (You can still set a class attribute on Outer to Inner, if you want.)

I think you can simply do:
class OuterClass:
outer_var = 1
class InnerClass:
pass
InnerClass.inner_var = outer_var
The problem you encountered is due to this:
A block is a piece of Python program text that is executed as a unit.
The following are blocks: a module, a function body, and a class
definition.
(...)
A scope defines the visibility of a name within
a block.
(...)
The scope of names defined in a class block is
limited to the class block; it does not extend to the code blocks of
methods – this includes generator expressions since they are
implemented using a function scope. This means that the following will
fail:
class A:
a = 42
b = list(a + i for i in range(10))
http://docs.python.org/reference/executionmodel.html#naming-and-binding
The above means:
a function body is a code block and a method is a function, then names defined out of the function body present in a class definition do not extend to the function body.
Paraphrasing this for your case:
a class definition is a code block, then names defined out of the inner class definition present in an outer class definition do not extend to the inner class definition.

You might be better off if you just don't use nested classes. If you must nest, try this:
x = 1
class OuterClass:
outer_var = x
class InnerClass:
inner_var = x
Or declare both classes before nesting them:
class OuterClass:
outer_var = 1
class InnerClass:
inner_var = OuterClass.outer_var
OuterClass.InnerClass = InnerClass
(After this you can del InnerClass if you need to.)

Easiest solution:
class OuterClass:
outer_var = 1
class InnerClass:
def __init__(self):
self.inner_var = OuterClass.outer_var
It requires you to be explicit, but doesn't take much effort.

In Python mutable objects are passed as reference, so you can pass a reference of the outer class to the inner class.
class OuterClass:
def __init__(self):
self.outer_var = 1
self.inner_class = OuterClass.InnerClass(self)
print('Inner variable in OuterClass = %d' % self.inner_class.inner_var)
class InnerClass:
def __init__(self, outer_class):
self.outer_class = outer_class
self.inner_var = 2
print('Outer variable in InnerClass = %d' % self.outer_class.outer_var)

All explanations can be found in Python Documentation The Python Tutorial
For your first error <type 'exceptions.NameError'>: name 'outer_var' is not defined. The explanation is:
There is no shorthand for referencing data attributes (or other methods!) from within methods. I find that this actually increases the readability of methods: there is no chance of confusing local variables and instance variables when glancing through a method.
quoted from The Python Tutorial 9.4
For your second error <type 'exceptions.NameError'>: name 'OuterClass' is not defined
When a class definition is left normally (via the end), a class object is created.
quoted from The Python Tutorial 9.3.1
So when you try inner_var = Outerclass.outer_var, the Quterclass hasn't been created yet, that's why name 'OuterClass' is not defined
A more detailed but tedious explanation for your first error:
Although classes have access to enclosing functions’ scopes, though, they do not act
as enclosing scopes to code nested within the class: Python searches enclosing functions
for referenced names, but never any enclosing classes. That is, a class is a local scope
and has access to enclosing local scopes, but it does not serve as an enclosing local scope
to further nested code.
quoted from Learning.Python(5th).Mark.Lutz

class c_outer:
def __init__(self, name:str='default_name'):
self._name = name
self._instance_lst = list()
self._x = self.c_inner()
def get_name(self):
return(self._name)
def add_inner_instance(self,name:str='default'):
self._instance_lst.append(self.c_inner(name))
def get_instance_name(self,index:int):
return(self._instance_lst[index].get_name())
class c_inner:
def __init__(self, name:str='default_name'):
self._name = name
def get_name(self):
return(self._name)
outer = c_outer("name_outer")
outer.add_inner_instance("test1")
outer.add_inner_instance("test2")
outer.add_inner_instance("test3")
inner_1 = outer.c_inner("name_inner1")
inner_2 = outer.c_inner("name_inner2")
inner_3 = outer.c_inner("name_inner3")
print(outer.get_instance_name(index=0))
print(outer.get_instance_name(1))
print(outer._instance_lst[2]._name
print(outer.get_name())
print(inner_1.get_name())
print(inner_2.get_name())
test1
test2
test3
name_outer
name_inner1
name_inner2
name_inner3

Creating objects within an existing object in Python

I would like to create an object that holds and creates different objects within itself.
I have an outer class and inner classes, like this:
class Outer:
def __init__(self, name):
self.name = name
def sayHello(self):
print "Hello " + self.name
class Inner1:
def __init__(self, name):
self.name = name
class Inner2(Inner1):
pass
class Inner3(Inner1):
pass
new = outer("new")
And then new needs to make on object of inner2 or inner3...
I tried it with new.inner2()
but I don´t get the result I want.
Any tips?

Here is how you would do nested classes and nested instantiations. When you're embedding the classes, you're only embedding the types. You have to create the instances in self.__init__
(If you're trying to do global inner instances shared among all Outer instances please update your question.)
class Outer(object):
class Inner1(object):
pass
class Inner2(Inner1):
pass
class Inner3(Inner2):
pass
def __init__(self):
self.inner1 = Outer.Inner1()
self.inner2 = Outer.Inner2()
self.inner3 = Outer.Inner3()
outer = Outer()
print outer.inner1
print outer.inner2
print outer.inner3
Note that you don't have to actually use nested classes for this -- your classes can be defined outside of your class, and is sometimes preferred as simpler and more Pythonic:
class Inner1(object):
pass
class Inner2(Inner1):
pass
class Inner3(Inner2):
pass
class Outer(object):
def __init__(self):
self.inner1 = Inner1()
self.inner2 = Inner2()
self.inner3 = Inner3()
outer = Outer()
print outer.inner1
print outer.inner2
print outer.inner3
Sometimes you'll also see a pattern of...
class Inner1(object):
pass
class Outer(object):
Inner1 = Inner1
to make a "handy" reference to the class inside the class. This is often used with custom exceptions that the class might throw.
There are many different opinions on whether nesting the classes is preferred.

Honestly inner classes are not generally a good idea, especially if you're instantiating them outside of the "containing" class.
But to answer your question, basically the inner class is just declared in a different scope, so you need to reference the scope it is in.
# Changed to a capitol letter as that is more conventional
class Outer:
name = ""
def __init__(self, name):
self.name = name
def sayHello(self):
print ("Hello" + self.name)
class Inner1:
def __init__(self, name):
self.name = name
class Inner2(Inner1):
pass
class Inner3(Inner1):
pass
newOuter = Outer("newOuter")
newInner2 = Outer.Inner2("newInner2")

How do I call a parent class's method from a child class in Python?

When creating a simple object hierarchy in Python, I'd like to be able to invoke methods of the parent class from a derived class. In Perl and Java, there is a keyword for this (super). In Perl, I might do this:
package Foo;
sub frotz {
return "Bamf";
}
package Bar;
#ISA = qw(Foo);
sub frotz {
my $str = SUPER::frotz();
return uc($str);
}
In Python, it appears that I have to name the parent class explicitly from the child.
In the example above, I'd have to do something like Foo::frotz().
This doesn't seem right since this behavior makes it hard to make deep hierarchies. If children need to know what class defined an inherited method, then all sorts of information pain is created.
Is this an actual limitation in python, a gap in my understanding or both?

Use the super() function:
class Foo(Bar):
def baz(self, **kwargs):
return super().baz(**kwargs)
For Python < 3, you must explicitly opt in to using new-style classes and use:
class Foo(Bar):
def baz(self, arg):
return super(Foo, self).baz(arg)

Python also has super as well:
super(type[, object-or-type])
Return a proxy object that delegates method calls to a parent or sibling class of type.
This is useful for accessing inherited methods that have been overridden in a class.
The search order is same as that used by getattr() except that the type itself is skipped.
Example:
class A(object): # deriving from 'object' declares A as a 'new-style-class'
def foo(self):
print "foo"
class B(A):
def foo(self):
super(B, self).foo() # calls 'A.foo()'
myB = B()
myB.foo()

ImmediateParentClass.frotz(self)
will be just fine, whether the immediate parent class defined frotz itself or inherited it. super is only needed for proper support of multiple inheritance (and then it only works if every class uses it properly). In general, AnyClass.whatever is going to look up whatever in AnyClass's ancestors if AnyClass doesn't define/override it, and this holds true for "child class calling parent's method" as for any other occurrence!

Python 3 has a different and simpler syntax for calling parent method.
If Foo class inherits from Bar, then from Bar.__init__ can be invoked from Foo via super().__init__():
class Foo(Bar):
def __init__(self, *args, **kwargs):
# invoke Bar.__init__
super().__init__(*args, **kwargs)

Many answers have explained how to call a method from the parent which has been overridden in the child.
However
"how do you call a parent class's method from child class?"
could also just mean:
"how do you call inherited methods?"
You can call methods inherited from a parent class just as if they were methods of the child class, as long as they haven't been overwritten.
e.g. in python 3:
class A():
def bar(self, string):
print("Hi, I'm bar, inherited from A"+string)
class B(A):
def baz(self):
self.bar(" - called by baz in B")
B().baz() # prints out "Hi, I'm bar, inherited from A - called by baz in B"
yes, this may be fairly obvious, but I feel that without pointing this out people may leave this thread with the impression you have to jump through ridiculous hoops just to access inherited methods in python. Especially as this question rates highly in searches for "how to access a parent class's method in Python", and the OP is written from the perspective of someone new to python.
I found:
https://docs.python.org/3/tutorial/classes.html#inheritance
to be useful in understanding how you access inherited methods.

Here is an example of using super():
#New-style classes inherit from object, or from another new-style class
class Dog(object):
name = ''
moves = []
def __init__(self, name):
self.name = name
def moves_setup(self):
self.moves.append('walk')
self.moves.append('run')
def get_moves(self):
return self.moves
class Superdog(Dog):
#Let's try to append new fly ability to our Superdog
def moves_setup(self):
#Set default moves by calling method of parent class
super(Superdog, self).moves_setup()
self.moves.append('fly')
dog = Superdog('Freddy')
print dog.name # Freddy
dog.moves_setup()
print dog.get_moves() # ['walk', 'run', 'fly'].
#As you can see our Superdog has all moves defined in the base Dog class

There's a super() in Python too. It's a bit wonky, because of Python's old- and new-style classes, but is quite commonly used e.g. in constructors:
class Foo(Bar):
def __init__(self):
super(Foo, self).__init__()
self.baz = 5

I would recommend using CLASS.__bases__
something like this
class A:
def __init__(self):
print "I am Class %s"%self.__class__.__name__
for parentClass in self.__class__.__bases__:
print " I am inherited from:",parentClass.__name__
#parentClass.foo(self) <- call parents function with self as first param
class B(A):pass
class C(B):pass
a,b,c = A(),B(),C()

If you don't know how many arguments you might get, and want to pass them all through to the child as well:
class Foo(bar)
def baz(self, arg, *args, **kwargs):
# ... Do your thing
return super(Foo, self).baz(arg, *args, **kwargs)
(From: Python - Cleanest way to override __init__ where an optional kwarg must be used after the super() call?)

There is a super() in python also.
Example for how a super class method is called from a sub class method
class Dog(object):
name = ''
moves = []
def __init__(self, name):
self.name = name
def moves_setup(self,x):
self.moves.append('walk')
self.moves.append('run')
self.moves.append(x)
def get_moves(self):
return self.moves
class Superdog(Dog):
#Let's try to append new fly ability to our Superdog
def moves_setup(self):
#Set default moves by calling method of parent class
super().moves_setup("hello world")
self.moves.append('fly')
dog = Superdog('Freddy')
print (dog.name)
dog.moves_setup()
print (dog.get_moves())
This example is similar to the one explained above.However there is one difference that super doesn't have any arguments passed to it.This above code is executable in python 3.4 version.

In this example cafec_param is a base class (parent class) and abc is a child class. abc calls the AWC method in the base class.
class cafec_param:
def __init__(self,precip,pe,awc,nmonths):
self.precip = precip
self.pe = pe
self.awc = awc
self.nmonths = nmonths
def AWC(self):
if self.awc<254:
Ss = self.awc
Su = 0
self.Ss=Ss
else:
Ss = 254; Su = self.awc-254
self.Ss=Ss + Su
AWC = Ss + Su
return self.Ss
def test(self):
return self.Ss
#return self.Ss*4
class abc(cafec_param):
def rr(self):
return self.AWC()
ee=cafec_param('re',34,56,2)
dd=abc('re',34,56,2)
print(dd.rr())
print(ee.AWC())
print(ee.test())
Output
56
56
56

In Python 2, I didn't have a lot luck with super(). I used the answer from
jimifiki on this SO thread how to refer to a parent method in python?.
Then, I added my own little twist to it, which I think is an improvement in usability (Especially if you have long class names).
Define the base class in one module:
# myA.py
class A():
def foo( self ):
print "foo"
Then import the class into another modules as parent:
# myB.py
from myA import A as parent
class B( parent ):
def foo( self ):
parent.foo( self ) # calls 'A.foo()'

class department:
campus_name="attock"
def printer(self):
print(self.campus_name)
class CS_dept(department):
def overr_CS(self):
department.printer(self)
print("i am child class1")
c=CS_dept()
c.overr_CS()

If you want to call the method of any class, you can simply call Class.method on any instance of the class. If your inheritance is relatively clean, this will work on instances of a child class too:
class Foo:
def __init__(self, var):
self.var = var
def baz(self):
return self.var
class Bar(Foo):
pass
bar = Bar(1)
assert Foo.baz(bar) == 1

class a(object):
def my_hello(self):
print "hello ravi"
class b(a):
def my_hello(self):
super(b,self).my_hello()
print "hi"
obj = b()
obj.my_hello()

This is a more abstract method:
super(self.__class__,self).baz(arg)