Python’s built-in object() function takes no argument and returns a new featureless object—the base and parent of all classes. As such it provides all methods that are common to all Python class instances such as __repr__() and other “dunder” methods. However, unlike for all non-object instances, you cannot assign arbitrary attributes to an instance of the object class—this is because of Python’s lack of the method __dict__().
| Argument | - | – |
| Return Value | object | Returns a new instance of the object class. |
>>> object() <object object at 0x0000020A4201E3A0> >>> help(obj) Help on object object: class object | The most base type
Two objects created with object() are always unique which makes them an excellent choice for implementing the sentinel pattern:
>>> object() == object() False >>> object() is object() False
Python object() Video
What is the Purpose of Python object()?
The fact that the instance returned by the constructor object() doesn’t provide a __dict__() method implementation means that you cannot add attributes to the object instance. It may seem to you that this makes it essentially useless—you cannot create your custom class with custom methods and attributes. However, the object() function is often used to create a sentinel object or dummy data when None cannot be used—for instance if None is part of the valid data in a list and you want to iterate until you find the sentinel data object().
Next, I’ll show you an example of this:
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So, here’s an example of the use of object() as sentinel data. We use a single object instance as input to the built-in iter() function that keeps iterating and ask the user for some input until the user enters 'stop'. Only then does the iterator function step() return the sentinel “dummy” object that causes the main loop to terminate:
sentinel = object()
def step():
user_input = input('your number: ')
if user_input == 'stop':
return sentinel
return user_input
for user_input in iter(step, sentinel):
print('your input: ', user_input)
One of my test runs turned out like this:
>>> your number: 2 your input: 2 your number: 2 your input: 2 your number: 2 your input: 2 your number: 42 your input: 42 your number: stop
It keeps looping until I put in 'stop'. This causes the function to return the sentinel object which terminates the iterator.
The advantage of using a unique object() object as a sentinel object compared to None is that object() creates a unique object but None does not.
Summary
Python’s built-in object() function takes no argument and returns a new featureless object—the base and parent of all classes.
As such it provides all methods that are common to all Python class instances such as __repr__() and other “dunder” methods.
However, unlike for all non-object instances, you cannot assign arbitrary attributes to an instance of the object class—this is because of Python’s lack of the “dunder” __dict__() method.
>>> obj = object()
>>> obj.a = 2
Traceback (most recent call last):
File "<pyshell#15>", line 1, in <module>
obj.a = 2
AttributeError: 'object' object has no attribute 'a'Want to keep improving your Python skills? Check out our free Python cheat sheets:
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