A very simple memory DB like REDIS

sdb.py

def set(variable, value, varmap):
    varmap[variable]=int(value)

def get(variable, varmap):
    try:
    	ret=varmap[variable]
    except:
        ret="NULL"
    print(ret)

def unset(variable, varmap):
	del varmap[variable]

def numequalto(value, varmap):
    print(len([k for k,v in varmap.iteritems() if varmap[k]==int(value)]))

def begin(varmap, level):
    return REPL(varmap, level=(level+1))
    
def commit(varmap, level):
    if level > 0:
        return varmap
    else:
        print("NO TRANSACTION")

common_fn = {
   'SET':set,
   'GET':get,
   'UNSET':unset,
   'NUMEQUALTO':numequalto,
}

transaction_fn = {
   'BEGIN':begin,
   'COMMIT':commit
}


def REPL(varmap=dict(), level=0):
    while True:
        cmd=raw_input("=>> ").split()
        if cmd[0] == "END":
            return False
        elif cmd[0] == "ROLLBACK":
            if level > 0:
                return
            else:
                print("NO TRANSACTION")
        elif cmd[0] in common_fn:
            cmd.append(varmap)
            common_fn[cmd[0]](*cmd[1::])
        elif cmd[0] in transaction_fn:
            x = transaction_fn[cmd[0]](varmap, level)
            if type(x) == dict:
                varmap.update(x)
                while level > 0:
                    return varmap
        else:
            print("Invalid Command") 


if __name__=="__main__":
    try:
        REPL()
    except:
        print("Goodbye")