python 表达式 语句 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 - 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