Question

I would like to pass a storage container location to a class. Is there a better way to do it than by passing a dict and the key? Passing keys feels a little odd, though it seems to work.

class GuiWidget():
    def __init__(self, storageDict, storageDictKey):
        self.storageDict = storageDict
        self.storageDictKey = storageDictKey
    def inc(self):
        self.storageDict[self.storageDictKey] += 1  # in real problem store image

storage = {"k1":0, "k2":0}

w1 = GuiWidget(storage, "k1")
w2 = GuiWidget(storage, "k2")


# calls from gui thread
print storage
w1.inc()
print storage
w2.inc()
print storage

##{'k2': 0, 'k1': 0}
##{'k2': 0, 'k1': 1}
##{'k2': 1, 'k1': 1}

—edit—

Though I would do it a little more verbosely, I like Andrey’s way. It works with either dict or list. It also gave me the idea for this solution with a class, though the differences in use seem more cosmetical:

class GuiWidget(object):
    def __init__(self, connector):
        self.connector = connector
    def inc(self):
        self.connector.v = (self.connector.v + 1)

class Connector(object):
    def __init__(self, container, key):
        self.container = container
        self.key = key
    def get_f(self):
        return self.container[self.key]
    def set_f(self, z):
        self.container[self.key] = z
    v = property(fget=get_f, fset=set_f)

storage = {"k1":0, "k2":0}
storageList = [0]

w1 = GuiWidget(Connector(storage, "k1"))
w2 = GuiWidget(Connector(storage, "k2"))
w3 = GuiWidget(Connector(storageList, 0))


# calls from gui thread
print storage
w1.inc()
print storage
w2.inc()
print storage
w3.inc()
print storageList

##{'k2': 0, 'k1': 0}
##{'k2': 0, 'k1': 1}
##{'k2': 1, 'k1': 1}
##[4]

All this reminds me of passing a pointer to a struct in C.

Answer 1

I guess you want to eliminate the dependence of your class on storage access method. That’s my solution:

class GuiWidget():
    def __init__(self, accessFunc):
        self.accessFunc = accessFunc
    def inc(self):
        self.accessFunc(self.accessFunc() + 1)

storage = {"k1":0, "k2":0}

def getAccessFunc(key):
    return lambda v = None: v is not None and storage.update({key: v}) or storage[key]

w1 = GuiWidget(getAccessFunc("k1"))
w2 = GuiWidget(getAccessFunc("k2"))


# calls from gui thread
print storage
w1.inc()
print storage
w2.inc()
print storage