练习题目 ：if for while else range、xrange、zip

range在内存中直接生成指定的序列，当序列非常大时会浪费内存资源；

xrange则不会直接生成一个list，而是每次调用返回其中的一个值，而非直接全部生成存于内存中 

range([start,] stop[, step])

if练习：

#练习1：逐一显示指定列表中的所有元素：
a = ['first', 'second', 'third', 'forth', 'fifth']
count = 0
while count < len(a):
    print(a[count])
    count += 1

print('这是逆序显示'.center(30, '#'))
while a:
    print(a[-1])
    a.pop()

对于任何可迭代对象，使用for是最简单的,效率高于while

#练习2：求100内奇数和，偶数和：
a = 0
sum = 0
sum1 = 0
while a <= 100:
    if a % 2 != 0:
        sum += a
    else:
        sum1 += a
    a += 1

print('偶数和：%d ， 奇数和：%d' % (sum,sum1))
#偶数和：2500 ， 奇数和：2550



# 练习3：逐一显示指定列表的所有键，并于显示结束后说明总键数
a = []
dic = {'x': 1, 'b': 2, 'c': 3, 'd': 4}
keylist = dic.keys()
for i in keylist:
    a.append(i)

while a:
    print(a[0])
    a.pop(0)
else:
    print('总键数：%d'.center(50, '-') % (len(dic)))



#练习4：创建一个包含了100以内所有奇数的列表,并逆序显示列表中的所有元素：
a = 0
l = []
while a < 100:
    if a % 2 != 0:
        l.append(a)
    a += 1
else:
    print('正序:', l)
    l.reverse()
    m = l
    print('逆序：', l)
#逆序用到列表的reverse方法


#练习5：列表l = [0,1,2,3,4,5,6] m = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]，
#以第一个列表中的元素为键，以第二个列表中的元素为值生成字典L

l = [0, 1, 2, 3, 4, 5, 6]
m = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]
L = {}
count = 0
if len(l) == len(m):
    while count < len(l):
        L[l[count]] = m[count]
        count += 1
    else:
        print(L)

#涉及到字典中新增键值的方法==》给键直接赋值即可

##字典的构造：zip，取一个或多个序列为参数，将给定序列中的并排的元素配成元组，返回这些元组的列表（当参数长度不通时，zip以最短序列的长度为准）
#可在for循环中用于实现并行迭代
# L = [0, 1, 2, 3, 4, 5, 6]
# m = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]
# n = {}
# for (k,v) in zip(L,m):
#     n[k] = v
# print(n)
#输出：{0: 'Sun', 1: 'Mon', 2: 'Tue', 3: 'Wed', 4: 'Thu', 5: 'Fri', 6: 'Sat'}

for循环练习
练习1：逐一分开显示指定字典d1中的所有元素，类似如下：
       k1 v1
       k2 v2
       ...
d1 = {0: 'Sun', 1: 'Mon', 2: 'Tue', 3: 'Wed', 4: 'Thu', 5: 'Fri', 6: 'Sat'}
# d1 = {'0': 'Sun', '1': 'Mon', '2': 'Tue', '3': 'Wed', '4': 'Thu', '5': 'Fri', '6': 'Sat'}
for (k, v) in d1.items():
    print(k, v)



练习2：逐一显示列表中l1=["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]中的索引为奇数的元素
l1 = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]
法1：
for i in l1:
    if l1.index(i) % 2 != 0:
        print(l1[l1.index(i)])
法2：
for i in range(1,len(l1),2):  #非完全遍历用range
    print(l1[i])


练习3：将属于列表l1=["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]，
但不属于列表l2=["Sun", "Tue", "Wed", "Fri"]的所有元素定义为一个新列表l3
l1 = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]
l2 = ["Sun", "Tue", "Wed", "Fri"]
l3 = []
for i in l1:
    if i not in l2:
        l3.append(i)
print(l3)

练习4：已知列表namelist=['stu1', 'stu2', 'stu3', 'stu4', 'stu5', 'stu6', 'stu7'],
删除列表removelist=['stu3', 'stu7', 'stu9']：从namelist中移除removelist，不在removelist中的忽略
namelist = ['stu1', 'stu2', 'stu3', 'stu4', 'stu5', 'stu6', 'stu7']
removelist = ['stu3', 'stu7', 'stu9']
for i in removelist:
    if i in namelist:
        namelist.remove(i)
print(namelist)