Python基础-程序控制结构

学习自马哥Python

while

while bool_expression:
    while_suite
else:
    else_suite

• break：跳出最内层的循环
• continue：跳到所处的最近层循环的开始处
• pass：定位语句
• else代码块：循环正常终止才会执行，如果循环终止是由break跳出导致的，则else不会执行；

练习

>>> A = 7
>>> B = 9
>>> max = A if A > B else B
>>> print(max)
9

while

>>> url = 'www.magedu.com'
>>> while url:
	print url
	
SyntaxError: Missing parentheses in call to 'print'
>>> while url:
	print(url)
	url = url[1:]

	
www.magedu.com
ww.magedu.com
w.magedu.com
.magedu.com
magedu.com
agedu.com
gedu.com
edu.com
du.com
u.com
.com
com
om
m

while从后往前

url = 'www.zdw.com'
while url:
    print(url)
    url = url[:-1]
else:
    print("game over.")
C:\Python35\python3.exe D:/Python/day1/day14.py
www.zdw.com
www.zdw.co
www.zdw.c
www.zdw.
www.zdw
www.zd
www.z
www.
www
ww
w
game over.

打印1-100

>>> x = 0; y = 100
>>> while x < y:
	print(x)
	x +=1

Python2.7不换行打印1-100

In [1]: x = 0; y = 100

In [2]: while x < y: 
   ...:     print x,
   ...:     x += 1
   ...:     
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99

练习

• 练习1：逐一显示指定列表中的所有元素；

In [7]: l1 = [1,2,3,4]

In [8]: count = 0

In [9]: while count < len(l1):
   ...:     print l1[count]
   ...:     count +=1
   ...:     
1
2
3
4

第二种

In [10]: while l1:
   ....:     print l1[0]
   ....:     l1.pop(0)
   ....:     
1
2
3
4

• 练习2：求100以内所有偶数之和；

total = 0
for i in range(0, 100, 2):
#    print(i)
    total += i
print(total)

• 练习3：逐一显示指定字典的所有键；并于显示结合后说明总键数；

d1 = {'x':1, 'y':23, 'z':78}
keylist = d1.keys()
while keylist:
    print keylist[0]
    keylist.pop(0)
else:
    print len(d1)
    
C:\Python27\python.exe D:/Python/day1/day14.py
y
x
z
3  

• 练习4：创建一个包含了100以内所有奇数的列表；

l1 = []
x = 1
while x < 100:
    l1.append(x)
    x += 2
print l1

• 练习5：逆序逐一显示一个列表的所有元素

l1 = []
x = 1
while x < 100:
    l1.append(x)
    x += 2
print l1[::-1]

• 练习6：列表l1=[0,1,2,3,4,5,6]，列表l2=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]，以第一个列表的元素为键，以第二个列表中的元素为值生成字典d1;

d1 = {}
count = 0
l1=[0,1,2,3,4,5,6]
l2=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]
while count < len(l1):
    d1[l1[count]] = l2[count]
    count +=1
print d1

C:\Python27\python.exe D:/Python/day1/day14.py
{0: 'Sun', 1: 'Mon', 2: 'Tue', 3: 'Wed', 4: 'Thu', 5: 'Fri', 6: 'Sat'}