python3 学习

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1:    print语句:

        str = input("please input a string:\n");
        print("the string is: %s", str);                             #输出一个字符串.

        str1 = input("a:\n");
        d     = input("a number: \n");
        print("a: %s, d:%d\n"   % (str1,  int(d)));                #输出多个参数

2.    类型转换;
       强制转换成int:               int(var);
       强制转换成string:         str(var);

3.    数组：

       定义数组:                a = [ 1, 2, 3, 4, 5 ];
                                        a = [ "name1", "name2", "name3" ] ;
                                        a = [ 'a', 'b', 'c', 'd', 'e' ];
                                        a = [ 0 for i in range(10) ];                         #创建10个数组元素并初始化为0
                                        a = range(5);                                            #创建[ 0, 1, 2, 3, 4 ]
                                        a = range(1, 10, 2);                                 #创建[ 1, 3, 5, 7, 9 ]
                                        a = [  [1, 2, 3, 4], [5, 6, 7, 8], [9, 10]]       #创建二维数组

       取数组大小:            len(a);
       访问数组元素:        print(a[n]);
       访问数组的部分： print( a[n1:n2] );              # 访问下标在 >=n1 & <n2的范围.    n1,n2可以是负数,   但n1 必须 < n2
                                        print( a[: n1]);                   # 访问下标从0到n1(不包括n1)的范围
                                        print( a[n1:]);                    # 访问下标从n1到最后的范围
                                        print(a[0][0]);                    #访问二组数组
       数组的操作：         del a[n];                            #删除数组元素
                                        a.append(var)                #追加元素
                                        a.insert(index,var)
                                        a.pop(var)                       #返回最后一个元素，并从list中删除之
                                        a.remove(var)                #删除第一次出现的该元素
                                        a.count(var)                   #该元素在列表中出现的个数
                                        a.index(var)                   #该元素的位置,无则抛异常
                                        a.extend(list)                 #追加list，即合并list到L上
                                        a.sort()                           #排序
                                        a.reverse()                    #倒序
                                        a + b                              # 合并

       数组的遍历：        for ele in arr:
                                               print(ele);

运算符:

        算术运算符:   + - * / %    //(整除)   **(幂)，    0xFF(十六进制)  070(八进制)

        数学函数库：
                                pow(a,b),    abs(),   round(n)  
                                math.floor(n)   取整.        from math import floor.     只导入floor函数。  或  foo=math.floor;    foo(x)    用foo来代替floor.
                                import    math;       导入math模块.
                                math.sqrt()        开平方.

字符串与变量：

        字符串转换:     str(data);       将data转换成 str;

                                  repr(data);     将data的内容转换成字符串，有点像shell中的反引号(变量展开)。