python中表达式和语句及for、while循环练习
1)表达式
常用的表达式操作符：
x + y, x - y
x * y, x / y, x // y, x % y
逻辑运算：
x or y, x and y, not x
成员关系运算：
x in y, x not in y
对象实例测试：
x is y, x not is y
比较运算：
x < y, x > y, x <= y, x >= y, x == y, x != y
位运算：
x | y, x & y, x ^ y, x << y, x >> y
一元运算：
-x, +x, ~x:
幂运算：
x ** y
索引和分片：
x[i], x[i:j], x[i:j:stride]
调用：
x(...)
取属性：
x.attribute
元组：(...)
序列：[...]
字典：{...}
三元选择表达式：x if y else z
匿名函数：lambda args: expression
生成器函数发送协议：yield x
运算优先级：
(...), [...], {...}
s[i], s[i:j]
s.attribute
s(...)
+x, -x, ~x
x ** y
*, /, //, %
+, -
<<, >>
&
^
|
<, <=, >, >=, ==, !=
is, not is
in, not in
not
and
or
lambda2)语句：
赋值语句
调用
print： 打印对象
if/elif/else: 条件判断
for/else: 序列迭代
while/else: 普通循环
pass: 占位符
break:
continue
def
return
yield
global: 命名空间
raise: 触发异常
import:
from: 模块属性访问
class: 类
try/except/finally: 捕捉异常
del: 删除引用
assert: 调试检查
with/as: 环境管理器
赋值语句：
隐式赋值：import, from, def, class, for, 函数参数
元组和列表分解赋值：当赋值符号(=)的左侧为元组或列表时，Python会按照位置把右边的对象和左边的目标自左而右逐一进行配对儿；个数不同时会触发异常，此时可以切片的方式进行；
多重目标赋值
增强赋值: +=, -=, *=, /=, //=, %=,3)for循环练习
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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 = { 'x':1,'y':2,'z':3,'m':4 }
>>> for (k,v) in d1.items():
print k,v
y 2
x 1
z 3
m 4
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"]
>>> for i in range(1,len(l1),2):
print l1[i]
Mon
Wed
Fri
练习3：将属于列表l1=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]，但不属于列表l2=["Sun","Mon","Tue","Thu","Sat"]的所有元素定义为一个新列表l3;
>>> l1 = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]
>>> l2 = ["Sun","Mon","Tue","Thu","Sat"]
>>> l3 = [ ]
>>> for i in l1:
if i not in l2:
l3.append(i)
>>> l3
['Wed', 'Fri']
练习4：已知列表namelist=['stu1','stu2','stu3','stu4','stu5','stu6','stu7']，删除列表removelist=['stu3', 'stu7', 'stu9']；请将属于removelist列表中的每个元素从namelist中移除(属于removelist，但不属于namelist的忽略即可)；
>>> namelist= ['stu1','stu2','stu3','stu4','stu5','stu6','stu7']
>>> removelist = ['stu3', 'stu7', 'stu9']
>>> for i in namelist:
if i in removelist :
namelist.remove(i)
>>> namelist
['stu1', 'stu2', 'stu4', 'stu5', 'stu6']4)while循环练习
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练习1：逐一显示指定列表中的所有元素；
>>> l1 = [1,2,3,4,5]
>>> i = 0
>>> while i < len(l1)
print l1[i]
i += 1
1
2
3
4
5
>>> l1 = [1,2,3,4,5]
>>> while l1:
print l1.pop(0)
1
2
3
4
5
练习2：求100以内所有偶数之和；
>>> i = 0
>>> sum = 0
>>> while i < 101:
sum += i
i += 2
print sum
2550
>>> for i in range(0,101,2):
sum+=i
print sum
2550
练习3：逐一显示指定字典的所有键；并于显示结束后说明总键数；
>>> d1 = {'x':1, 'y':23, 'z': 78}
>>> i1 = d1.keys()
>>> while i1:
print i1.pop(0)
else:
print len(d1)
x
y
z
3
练习4：创建一个包含了100以内所有奇数的列表；
>>> d1 = [ ]
>>> i = 1
>>> while i < 101:
d1.append(i)
i+=2
>>> print d1
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99]
>>> d1 = [ ]
>>> for i in range(1,101,2)
d1.append(i)
>>> print d1
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99]
练习5：列表l1=[0,1,2,3,4,5,6], 列表l2=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]，以第一个列表中的元素为键，以第二个列表中的元素为值生成字典d1；
>>> l1 = [0,1,2,3,4,5,6]
>>> l2 = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]
>>> d1 = {}
>>> count = 0
>>> if len(l1) == len(l2):
while count < len(l1):
d1[l1[count]] = l2[count]
count += 1 
