OOP in Python

Question 1

distinguish between local and instance variables

Answer 1

self.x

Question 2

“special features” of Python functions

Answer 2

functions are regular objects; passed as arguments, returned from function, modified inside functions etc.

Question 3

private variable

Answer 3

doesn’t exist

Question 4

constructor

Answer 4

class MyClass:
    def \_\_init\_\_(self, i, j):
        self.i = i; self.j = j;
    def write(self):
        print "i = %d" % (i)

Question 5

declaring and calling instance methods

Answer 5

all instance methods take self as first argument in the declaration, but no in the call

Question 6

obj. someMethod()

class. someMethod(obj)

Answer 6

equal for an instance obj of class class

Question 7

class variables

Answer 7

class variables are common to the class;

>>>class Point(object):
    counter = 0
    def \_\_init\_\_(self):
        Point.counter +=1
>>> p0 = Point()
>>> p1 = Point()
>>> Point.counter
2
>>> p0.counter
2

Question 8

get dictionary with all class attributes

Answer 8

Class.__dict__

instance.__class__.__dict__

Question 9

name of class

Answer 9

instance.__class__.__name__

Question 10

list names of all methods and attributes

Answer 10

dir(instance)

Question 11

python functions are also …

Answer 11

objects, and can therefore be arguments to functions

Question 12

function as argument to function

Answer 12

def apply(func, x, y):
    return func(x, y)

Question 13

nested function definitions

Answer 13

def f(x):
    def cube(x):
        return x*x*x
    return cube(x)

Question 14

return function from function

Answer 14

def outer():
    def inner():
        ....
    return inner

Question 15

decorate a function

Answer 15

@checkrange
def g(x):
    return x**3-2

# or
g = checkrange(g)