minimum = int()
highest = int()
while(True):
    num = int(input("Enter a Number (Use -1 to Stop): " ))  
    if highest < num:
        highest = num
    if minimum > num:
        minimum = num  
    if(num == -1):
        break      
   
print("The interval is",minimum,"-", highest)

# usually it's not good to
# set a name to None
# and afterwards to an integer
minimum = None # not set yet
maximum = None # not set yet
# if you forget this, you'll run
# into a TypeError, happens for example with comparison < or >


while True: # <- no parenthesis needed
    user_input = input("Enter a Number (q|Q to quit): ")
    if user_input.lower() == 'q':
        break
    try:
        num = int(user_input)
    except ValueError:
        print(user_input, 'is not a valid integer')
        # ask again for user input
        continue
    if minimum is None:
        # the first time minimum and maximum
        # is None
        # Just setting minimum
        # and maximum to the first user input
        # this this will never again executed
        minimum = num
        maximum = num
        # the code afterwards will be executed
        # but does no change to the value
    if maximum < num:
        maximum = num
    if minimum > num:
        minimum = num
    # fancy format string: Python 3.6+
    # first minimum and maximum is equal
    print(f"The interval is {minimum} -> {maximum}")


print('Program ends here')

answers = []

while (answer := input('Enter a number (q|Q) to quit): ').lower()) != 'q':
    try:
        answers.append(int(answer))
    except ValueError:
        print(f'Expected integer but got {answer!r}')

if answers:
    print(f'Mininum value {min(answers)} and maximum value {max(answers)}')
else:
    print('No integers entered!')