python 表达式和语句及for、while循环练习实例

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 

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 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']

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 += 2print 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