Python list should be empty on class instance initialisation, but it's not. Why?
- by canavanin
Hi everyone!
I would like to create instances of a class containing a list that's empty by default; instead of later setting this list to the final full list I would like to successively add items to it. Here's a piece of sample code illustrating this:
#!/usr/bin/python
class test:
def __init__(self, lst=[], intg=0):
self.lista = lst
self.integer = intg
name_dict = {}
counter = 0
for name in ('Anne', 'Leo', 'Suzy'):
counter += 1
name_dict[name] = test()
name_dict[name].integer += 1
name_dict[name].lista.append(counter)
print name, name_dict[name].integer, name_dict[name].lista
When I ran the above program I expected to get
Anne 1 [1]
Leo 1 [2]
Suzy 1 [3]
as I assumed lista to always be initialised to an empty list.
What I got instead was this:
Anne 1 [1]
Leo 1 [1, 2]
Suzy 1 [1, 2, 3]
If I replace self.lista = lst by self.lista = [] it works fine, just like when I add the line name_dict[name].lista = [] to the for loop.
Why is it that the contents of the previous objects' lists are retained, yet their values of integer aren't? I am rather new to Python, so it would be great if someone could point out to me where my thoughts/assumptions have gone astray.
Thanks a lot in advance for your replies.
