human
I am working on the file "Lecture4.ipynb".
The first task is:
Aside: __repr__, __call__,__getitem__,...  are all awesome.
Can you write Python code for it?
 ... Write me a the Python code you requested?
assistant
#Here is the Python code you requested.

class foo():
    "Me is foo"
    def __init__(i, num):
        i.num = num
    def __add__(i, new):
        i.num += new
        return i
    def __sub__(i, new):
        i.num -= new
        return i
    def __repr__(i):
        return i.__doc__
    def __getitem__(i, num):
        print "Nothing @ %d"%(num)

FOO = foo(4)
FOO[2]