控制流程

#!/usr/bin/python
i = 5
print i
i = i + 1
print i
s1 = '''This is a multi-line string.\
This is the second line.'''
s2 = '''This is a multi-line string.
This is the second line.'''
print s1
print s2

#!/usr/bin/python
# Filename:expression.py
length = 5
breadth = 2
area = length * breadth
print 'Area is', area
print 'Perimeter is', 2 * (length + breadth)

使用if语句
#!/usr/bin/python
# Filename: if.py
number = 23
guess = int(raw_input('Enter an integer : '))

if guess == number:
    print 'Congratulations, you guessed it.'
    #New blockstarts here
    print "(but you do not win any prizes!)"
elif guess < number:
    print 'No, it is a little higher than that.'
    #Another block
else:
    print 'No, it is a little lower than that'

print 'Done'
# This last statement is always executed, after the ifstatement is executed
    
使用while语句
#!/usr/bin/python
# Filename: while.py
number = 23
running = True

while running:
    guess = int(raw_input('Enter an integer : '))
    
    if guess == number:
        print 'Congratulations, you guessed it.'
        running = False # this causes the while loop tostop
        
    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.'
    # Do anything else you want to do here
print 'Done'

#!/usr/bin/python
# Filename: while.py
number = 23
running = True

while running:
    guess = int(raw_input('Enter an integer : '))
    
    if guess == number:
        print 'Congratulations, you guessed it.'
        break #直接跳出while，下面的print 'The while loop is over.'不执行
        
    elif guess < number:
        print 'No, it is a little higher than that.'
    else:
        print 'No, it is a little lower than that.'
#当while循环条件变为False的时候，else块才被执行        
else:
    print 'The while loop is over.'
    # Do anything else you want to do here
print 'Done'
记住，你可以在while循环中使用一个else从句。

for循环
for..in是另外一个循环语句，它在一序列的对象上 递归 即逐一使用队列中的每个项目
#!/usr/bin/python
# Filename: for.py
for i in range(1, 5):
    print i
else:
    print 'The for loop is over.'
默认地，range的步长为1
如果我们为range提供第三个数，那么它将成为步长。例如，range(1,5,2)给出[1,3]。记住，range 向上 延伸到第二个数，即它不包含第二个数。
记住，else部分是可选的。如果包含else，它总是在for循环结束后执行一次，除非遇到break语句。
记住，for..in循环对于任何序列都适用。这里我们使用的是一个由内建range函数生成的数的列表，但是广义说来我们可以使用任何种类的由任何对象组成的序列！
如果你想要写for (int i = 0; i < 5; i++)，那么用Python，你写成for i in range(0,5)。