以缩进符和冒号标志语块：
#!/usr/bin/python
#Filename: if.py
number = 23
running = True
while running:
guess = int(input('Enter an integer : '))
if guess == number:
print('Congratulations,you guessed it.')
print('(but you do not win any prizes!)')
running = False
elif guess < number:
print('No,it is a little higher than that')
else:
print('No,it is a little lower than that')
else:
print('the while loop is over.')