Hello Group, I am puzzled about this: The following
code implements a simple FIFO object.
class Queue:
" Implementing a FIFO data structure."
# Methods
def __init__(self):
self.queue = []
def emptyP(self):
return (self.queue == [])
def insert(self, item):
self.queue.append(item)
def remove(self):
if not self.emptyP():
return self.queue.pop(0)
def __str__(self):
return str(self.queue)
This code works as intended. Now my idea is to provide
an optional argument to the constructor. So I change
it to:
def __init__(self, q =[]):
self.queue = q
Now, something very strange happens:
>>> a = Queue()
>>> b = Queue()
>>> a.insert(12)
>>> print b
[12]
>>>
Why do a and b share the same data? "self.queue" is
supposed to be an instance variable. What does may
change of the __init__ method do here?
Thanx for your help.
Barb
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