List of strings in a dictionary getting erroneously assigned a value

Question

I'm having a really bizarre issue in a program I'm writing. I'm trying to find an object in a dictionary, and if the name string in the object matches the name I'm looking for, then I append a message to the empty list. Afterwards, I would expect to have a list of a single string. What I'm actually getting though is quite surprising to me, and I can't for the life of me explain it.

clients     = {}    

class Client:           
my_fullname = ""
mymessage       = []

def send_message(recipient, message, clients):
for guy in clients:
    if clients[guy].my_fullname == recipient:
        print(clients[guy].my_fullname)
        print(clients[guy].mymessage)
        clients[guy].mymessage.append(message)
        return

SCOTT = Client()
SCOTT.my_fullname = "SCOTT"
KAT = Client()
KAT.my_fullname = "KAT"

clients["SCOTT"] = SCOTT
clients["KAT"] = KAT

print(clients["KAT"].mymessage)
send_message("KAT", "goodbye", clients)
print(clients["KAT"].mymessage)

print(clients["SCOTT"].mymessage)
send_message("SCOTT", "what's up", clients)
print(clients["SCOTT"].mymessage)

And here's the output I'm getting from running that. I'm on Python 2.7.5. I've tried having clients passed in as a parameter, I've tried having it as a global without passing it in, and I've tried having it as a global and not passing it in but declaring "global clients" at the beginning of the function and I get the same result regardless. Help please?

[]
KAT
[]
['goodbye']
['goodbye']
SCOTT
['goodbye']
['goodbye', "what's up"]

you have some totally wrong white-space formatting there, fix it and you might improve your response. — Russia Must Remove Putin, Mar 20 '14 at 04:01

score 2 · Accepted Answer · answered Mar 20 '14 at 04:14

Your problem is that your mymessage is a class attribute, so it is shared among all instances of the class. Make it an instance attribute by assigning it in the __init__ method. While you're at it, why not pass in the full name as well?

class Client:           
    def __init__(self, fullname):
        self.my_fullname = fullname
        self.mymessage   = []

List of strings in a dictionary getting erroneously assigned a value

1 Answers1