what is the chain function in python code example

Example 1: class chain methods python

class foo():
    def __init__(self, kind=None):
        self.kind = kind
    def my_print(self):
        print (self.kind)
        return self
    def line(self):
        self.kind = 'line'
        return self
    def bar(self):
        self.kind='bar'
        return self

Example 2: class chain methods python

a = foo()
a.line()
a.my_print()
a.bar()
a.my_print()

assert a.kind == 'bar'