''' Purpose: show a while statement
'''

# set loop decision variable
# this is our looking variable, set it to True by default
# this is the condition to keep running the while loop runs
# here we are looking for a 'yes' or a 'no'
looking_for_a_yes_or_no = True


# while loop is how you do the same actions (repeat) for some uncertain amount of time
#   until the testing expression is no longer True (aka the testing expression is False)
# while ( testing expression ) :
# while we are still looking for a 'yes' or a 'no'
#   we want to keep asking the user until we get a valid string that's either 'yes' or 'no'
#   if the user enters some other string, keep asking. Otherwise, we can stop asking
#   we don't know how long the loop will run for, that's why we use the while loop, instead of
#   a for loop
while ( looking_for_a_yes_or_no == True ) : # repeat while looking

    # get cleaned up response
    reply = input( 'Enter (yes / no): ' )   # ask for an input while we are still looking
    # want to look for exactly 'yes' or 'no'
    reply = reply.strip()
    reply = reply.lower()

    print( 'reply =', reply )

    # check for valid response.
    if ( reply in [ 'yes', 'no' ] ) :  # if the reply is the string 'yes' or the string 'no'
        # got one - then we end our search --> end the while loop
        looking_for_a_yes_or_no = False # SET OUR LOOKING VARIABLE TO FALSE --> we are no longer looking
        # so it is False that we are still looking for a yes or no
        # --> while loop will exit --> go to line 46
        # if the truth condition is not updated, THIS WILL RUN FOREVER (eventually crashes)

        # if this if statement is True, then we ignore the else part
    else:
        # else = reply is not the string 'yes' or the string 'no'
        print( 'reply was no good' )

    # the while loop will restart if reply was not 'yes' or 'no'

# when while loop finishes, print the reply
print( reply )


# way 2

# ask for an input first
reply = input( 'Enter yes/no: ' )
reply = reply.strip()
reply = reply.lower()

# while reply is not a string 'yes' or 'no'
#   2 ways to express this condition:
#       reply not in ['yes', 'no]
#       reply != 'yes' or reply != 'no'   (reply not equal to 'yes' OR reply not equal to 'no')

while ( reply not in ['yes', 'no'] ):
    # print a message
    print( 'reply was no good' )

    # then ask again and UPDATE THE VARIABLE THAT YOU USE IN THE CONDITIONAL
    # STATEMENT IN THE WHILE STATEMENT
    # if you do not update reply, then reply will continue to be the
    # string when you first asked the user
    # you NEED to update reply to the new value so that the while can eventually end
    # when the new reply string is a 'yes' or 'no'
    reply = input( 'Enter yes/no: ' )
    reply = reply.strip()
    reply = reply.lower()

# once reply is a string 'yes' or 'no', then print the reply
print( reply )