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