python fatrow in a dictionary

I want a dictionary which uses an array for multiple values.

a={}
a['tim@sy']=['123']

Now check if number 123 is stored against tim@sy

if '123' in a['tim@sy']:
    print ('There')

And finally add if not exists

if '123' in a['tim@sy']:
    print ('There')
else:
    a['tim@sy'].append('125')

As a class

class fatrowdict(object):

    def __init__(self):
        self.data={}

    def __iter__(self):
        for a in self.data:
            yield a

    def add(self,key,value):
        if key in self.data:
            if value in self.data[key]:
                return false
            else
                self.data[key].append(value)
                return true

        else:
            self.data[key]=[value]
            return true



    def find_key(self,k):
        if k in self.data:
            return True,self.data[k]
        else:
            return False,None