"learn to code" entries

Are there some students who can’t learn how to code?

Change tactics or give up: It's a crossroads many teachers face when students don't understand the code.

by David Blaikie | @davidbpython | September 17, 2015

I can never forget an evening late into a semester of my Introduction to Python course, during which I asked my students a question about user-defined classes. Here’s the code I had put on the board:


class MyClass(object):

    var = 0

    def __init__(self):                # called 
        MyClass.var = MyClass.var + 1

x = MyClass()                          # new instance created
y = MyClass()                          # new instance created

class MyClass(object):

var = 0

def __init__(self): # called

MyClass.var = MyClass.var + 1

x = MyClass() # new instance created

y = MyClass() # new instance created

As new information for this particular lesson, I informed them that every time a new MyClass instance is created, the __init__() method is called implicitly. In other words, the code above calls __init__() twice, and in executing the code in __init__(), the variable MyClass.var is being incremented — so this is also happening twice.

So, I asked them: after the above code is executed, what is the value of MyClass.var?

The hand of this class’ most enthusiastic student shot into the air.

“One!” He answered proudly. And for a moment my mouth stood open. Read more…