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