Python中表达式和语句及for、while循环实例代码

 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
 lambda

 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: +=, -=, *=, /=, //=, %=,

 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']

 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