python 表达式和语句及for、while循环练习实例

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 - yx * 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.attributes(...)+x, -x, ~xx ** y*, /, //, %+, -<<, >> &^|<, <=, >, >=, ==, !=is, not isin, not innotandorlambda 

2)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

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 v1k2 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']