Shamanth Chedde Shamanth Chedde - 22 days ago 10
Python Question

Class keeps printing none

I am creating a switchboard class that switches light switches on and off. I've figured out how to write the code but when I create my object and print it, it keeps printing None. I'm not sure what's wrong and why it prints None instead of the return statement "The following switches are on: " Even if none of the switches are on it should still print the string above. Can someone help me find out why it's printing out None instead of the string I want it to print?

def SwitchBoard(LightSwitch):
'''This class will create a switch board for the user to use with n
number of switches that is entered by the user'''

def __init__(self, num_switches):
'''
(SwitchBoard, int) -> NoneType
Given a value by the user, the function will create a switch board
'''
# create an empty list to be the switchboard with the desired amount
# of switches
self._listsw = []
# turn each switch to off
for index in range(num_switches):
self._listsw.append(0)


def __str__(self):
'''
(SwitchBoard) -> str
Returns in a string the switches on the switchboard that are on
'''
# create an empty string to store the on switches in
result = ""
for index in range(len(self._listsw)):
if(self._listsw[index] == 1):
result += str(index)
result += " "
return "The following switches are on: " + result

def which_switch(self):
'''
(SwitchBoard) -> list of int
Given a switchboard, the function will check to see which switches are
on and will return the following switches in order as a list on integers
'''
# create an empty list to store the on switches in
on_switches = []
# loop through the list to check each switch
for index in range(len(self._listsw)):
# check if the switch is on
if(self._listsw[index] == 1):
# if the switch is on, add it to the list
on_switches.append(index)
# return the list of on switches
return on_switches


def flip(self, n):
'''
(SwitchBoard, int) -> NoneType
Given a switch as an integer, the function will flip the state of the
desired switch on the switchboard. If it is on, it will be turned off.
If it is off, it will be turned on.
'''
for index in range(len(self._listsw)):
# check if the switch is on
if(self._listsw[n] == 1):
# if it is on, turn the switch off
self._listsw[n] = 0
# if the switch is off
elif(self._listsw[n] == 0):
# turn the switch on
self._listsw[n] = 1


def flip_every(self, n):
'''
(SwitchBoard, int) -> NoneType
Given an integer n, the function will flip the state of every nth
integer. If the integer is on, it will be turned off. If the integer is
off, it will be turned on.
'''
for index in range(0, len(self._listsw), n):
# check if the switch is on
if(self._listsw[index] == 1):
# if it is on, turn the switch off
self._listsw[index] = 0
# if the switch is off
elif(self._listsw[index] == 0):
# turn the switch on
self._listsw[index] = 1


def reset(self):
'''
(SwitchBoard) -> NoneTypen
When called, the function will reset the entire switchboad and all
switches will be turned off.
'''
# go through the switchboard
for index in range(len(self._listsw)):
# and turn every switch off
self._listsw[index] = 0

Answer

Very simple error: You are defining your class as a function.

Replace:

def SwitchBoard(LightSwitch):

with

class SwitchBoard(LightSwitch):

And you are good to go. As it currently stands, SwitchBoard is treated as a function with one argument which does not return anything...hence the None.