Python create empty class

Constructing classes¶

There are two basic ways of constructing classes in Python. The best known way is to use Python’s class statement. The other way is to use Python’s type() function. This page covers the statement way. type(name, bases, dict) is more powerful and sometimes more convenient. However, the statement approach is the better way to get started and in ordinary programming is the most convenient.

The empty class¶

We will start with the empty class, which is not as empty as it looks.

Like most Python objects, our empty class has a dictionary. The dictionary holds the attributes of the object.

Even though our class is empty, its dictionary (or more exactly dictproxy) is not.

>>> sorted(A.__dict__.keys()) ['__dict__', '__doc__', '__module__', '__weakref__'] 

Attributes __doc__ and __module__ are there for documentation, and to give better error messages in tracebacks. The other attributes are there for system purposes.

In addition, our class two attributes that are not even listed in the dictionary. The __bases__ attribute is the list of base classes provided in the original class statement.

The method resolution order (mro) attribute __mro__ is computed from the bases of the class. It provides support for multiple inheritance.

For now the important thing is that even the empty class has attributes. (For IronPython and Jython the attributes are slightly different.)

© Copyright 2011, Jonathan Fine. Revision 9c142f616b68 .

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How to create an empty class in Python?

A class in Python user-defined prototype for an object that defines a set of attributes that characterize any object of the class. The attributes are data members (class variables and instance variables) and methods, accessed via dot notation.

We can easily create an empty class in Python using the pass statement. This statement in Python do nothing. Let us see an example −

Create an empty class

Here, our class name is Amit −

Create an empty class with objects

Example

We can also create objects of an empty class and use it in our program −

class Amit: pass # Creating objects ob1 = Amit() ob2 = Amit() # Displaying print(ob1) print(ob2) 
 

Outpu

Create an empty class and set attributes for different objects

Example

In this example, we will create an empty class using the pass, but attributes will also be set for objects −

class Student: pass # Creating objects st1 = Student() st1.name = 'Henry' st1.age = 17 st1.marks = 90 st2 = Student() st2.name = 'Clark' st2.age = 16 st2.marks = 77 st2.phone = '120-6756-79' print('Student 1 = ', st1.name, st1.age, st1.marks) print('Student 2 = ', st2.name, st2.age, st2.marks, st2.phone) 
 

Output

Student 1 = Henry 17 90 Student 2 = Clark 16 77 120-6756-79

Using the pass statement, we can also create empty functions and loops. Let’s see −

Empty Function

Use the pass statement to write an empty function in Python −

# Empty function in Python def demo(): pass 

Above, we have created an empty function demo().

Empty if-else Statement

The pass statement can be used in an empty if-else statements −

a = True if (a == True) : pass else : print("False") 

Above, we have created an empty if-else statement.

Empty while Loop

The pass statement can also be used in an empty while loop −

cond = True while(cond == True): pass 

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How to create an empty class in Python?

Remember: is not an object of a class, object doesn’t mean class instance , because in Python classes and functions are objects at runtime just like class instances Solution 3: There is no in Python 2.7, you could use for immutable objects instead: Or : See also, How can I create an object and add attributes to it? I’m teaching a Python class on object-oriented programming and as I’m brushing up on how to explain classes, I saw an empty class definition: The example then goes on to define a name and other attributes for an object of this class: Interesting!

How to create an empty class in Python?

A class is a user-defined blueprint or prototype from which objects are created. Class can be considered as a user-defined data type. Generally, a class contains data members known as attributes of the class and member functions that are used to modify the attributes of the class. But have you ever wondered how to define an empty class i.e a class without members and member functions?

In Python, if we write something like the following, it would raise a SyntaxError .

File "gfg.py", line 5 ^ SyntaxError: unexpected EOF while parsing

In Python, to write an empty class pass statement is used. pass is a special statement in Python that does nothing. It only works as a dummy statement. However, objects of an empty class can also be created.

Python also allows us to set the attributes of an object of an empty class. We can also set different attributes for different objects. See the following example for better understanding.

obj1 Details: Name: Nikhil Office: GeeksforGeeksobj2 Details: Name: Abhinav Office: GeeksforGeeks Phone: 1234567889

Traceback (most recent call last): File "gfg.py", line 34, in print("Phone:", obj1.phone) AttributeError: 'Employee' object has no attribute 'phone' 

How to create an empty class in Python?, Python also allows us to set the attributes of an object of an empty class. We can also set different attributes for different objects. See the following example for better understanding. class Employee: pass obj1 = Employee () obj1.name = ‘Nikhil’ obj1.office = ‘GeeksforGeeks’ obj2 = Employee () obj2.name = ‘Abhinav’ obj2.office = ‘GeeksforGeeks’

Empty class object in Python

I’m teaching a Python class on object-oriented programming and as I’m brushing up on how to explain classes, I saw an empty class definition:

The example then goes on to define a name and other attributes for an object of this class:

john = Employee() john.full_name = "john doe" 

I’m wondering if there’s a way to dynamically define a function for an instance of a class like this? something like:

john.greet() = print 'Hello, World!' 

This doesn’t work in my Python interpreter, but is there another way of doing it?

A class is more or less a fancy wrapper for a dict of attributes to objects. When you instantiate a class you can assign to its attributes, and those will be stored in foo.__dict__ ; likewise, you can look in foo.__dict__ for any attributes you have already written.

This means you can do some neat dynamic things like:

class Employee: pass def foo(self): pass Employee.foo = foo 

as well as assigning to a particular instance. (EDIT: added self parameter)

john.greet = lambda : print( 'hello world!' ) 

EDIT : Thanks Thomas K for the note — this works on Python 3.2 and not for Python2, where print appeared to be statement . But this will work for lambda s, without statements (right? Sorry, I know only python3.2 (: )

You could also use «named tuples» from the collection standard module. Named tuples work like «ordinary» tuples but the elements have names and you can access the elements using the «dot syntax». From the collection docs:

>>> # Basic example >>> Point = namedtuple('Point', ['x', 'y']) >>> p = Point(11, y=22) # instantiate with positional or keyword arguments >>> p[0] + p[1] # indexable like the plain tuple (11, 22) 33 >>> x, y = p # unpack like a regular tuple >>> x, y (11, 22) >>> p.x + p.y # fields also accessible by name 33 >>> p # readable __repr__ with a name=value style Point(x=11, y=22) 

>>> from attrdict import AttrDict >>> my_object = AttrDict() >>> my_object.my_attribute = 'blah' >>> print my_object.my_attribute blah >>> 

Install attrdict from PyPI:

It’s useful in other situations too — like when you need attribute access to dict keys.

Oop — Empty class object in Python, I’m teaching a Python class on object-oriented programming and as I’m brushing up on how to explain classes, I saw an empty class definition: class Employee: …

Declaring empty class member in python

i am trying to read a tree structure file in python. I created a class to hold the tree objects. One of the members should hold the parent object. Since the parentObject member is of the same type as the class itself, I need to declare this as an empty variable of type «self».

How do I do that in python?

Thank you very much for your help.

In Python, you don’t declare variables as having any type. You just assign to them. A single variable can be assigned objects of different types in succession, if you wanted to do so. «self» is not the type but a naming convention used to refer to the current object, like «this» in Java / C++ (except in Python you could call it anything you wanted).

Since the parentObject member is of the same type as the class itself, I need to declare this as an empty variable of type «self».

No, you do not need to declare anything in Python. You just define things.

And self is not a type, but the conventional name for the first parameter of instance methods, which is set by the language to the object of the method.

class Tree(object): def __init__(self, label=None): self.label = label self.parent = None self.children = [] def append(self, node): self.children.append(node) node.parent = self 

And here’s how that could be used:

empty_tree = Tree() simple_tree = Tree() simple_tree.append(Tree('hello')) simple_tree.append(Tree('world')) 

I assume that for the root node, you want such an object. It’s much more Pythonic to say:

in your root object, than to create an empty object of type self.__class__ . For every other node object in the tree, self.parent should refer to the actual parent node.

Remember, in Python you don’t have ‘variables’, you have objects, and there is no need for self.parent to be of same type in all the instances of a class.

Empty class size in python, An empty class definition is still a class definition and hence a class object ( more here ): When a class definition is entered, a new namespace is …

Does there exist empty class in python?

Does there exist special class in python to create empty objects? I tried object(), but it didn’t allow me to add fields. I want to use it like this:

obj = EmptyObject() obj.foo = 'far' obj.bar = 'boo' 

Should I each time(in several independent scripts) define new class like this?

types.SimpleNamespace was introduced with Python 3.3 to serve this exact purpose. The documentation also shows a simple way to implement it yourself in Python, so you can add it to your pre-Python 3.3 setup and use it as if it was there (note that the actual implementation is done in C):

class SimpleNamespace (object): def __init__ (self, **kwargs): self.__dict__.update(kwargs) def __repr__ (self): keys = sorted(self.__dict__) items = ("<>=".format(k, self.__dict__[k]) for k in keys) return "<>(<>)".format(type(self).__name__, ", ".join(items)) def __eq__ (self, other): return self.__dict__ == other.__dict__ 

But of course, if you don’t need its few features, a simple class Empty: pass does just the same.

If you are looking for a place holder object to which you can add arbitrary static members, then the closest I got is an empty lambda function.

obj = lambda: None # Dummy function obj.foo = 'far' obj.bar = 'boo' print obj.foo, obj.bar # far boo 

Remember: obj is not an object of a class, object doesn’t mean class instance , because in Python classes and functions are objects at runtime just like class instances

There is no types.SimpleNamespace in Python 2.7, you could use collections.namedtuple() for immutable objects instead:

>>> from collections import namedtuple >>> FooBar = namedtuple('FooBar', 'foo bar') >>> FooBar('bar', 'foo') FooBar(foo='bar', bar='foo') 

>>> from argparse import Namespace >>> o = Namespace(foo='bar') >>> o.bar = 'foo' >>> o Namespace(bar='foo', foo='bar') 

You can create a new type dynamically with the fields you want it to have using the type function, like this:

x = type('empty', (object,), ) x.bar = 3 print(x.foo) 

This is not entirely what you want though, since it will have a custom type, not an empty type.

Variables — declaring empty class member in python, It’s much more Pythonic to say: self.parent = None in your root object, than to create an empty object of type self.__class__. For every other node object …

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