Ellipsis object in python

First, it’s a singleton. It’s the same object after pickle and unpickle unlike other objects: not the same one if deserialized.

print(... is Ellipsis)  # always True

Second, it’s common used as a sentinel value compared to None, especially when None is an acceptable value for a type. See:

def example_function(arg=None, default=...):
    if default is ...:
        print("Default value not provided.")
    else:
        print(f"Default value is {default}")

example_function(None) # Default value is None

Third, it’s the replacement of pass to indicate a function is not yet implemented.

def unimplemented():
		...