Python中语句结构

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1if语句的格式
 
                if test1:
 
                                statement1
 
                elif test2:
 
                                statement2
 
                else
 
                                statement3
 
2、在python中没有switch/case语句,可以通过字典或者if,elif,else模拟
 
                例如:
 
                choice = ‘ham‘
 
                print({‘spam‘:1.25,‘ham‘:1.99,‘eggs‘:0.99,‘bacon‘:1.10}[choice])
 
                或者:
 
                if choice == ‘spam‘:
 
                                print(1.25)
 
                elif choice == ‘ham‘:
 
                                print(1.99)
 
                elif choice == ‘eggs‘:
 
                                print(0.99)
 
                elif choice == ‘bacon‘:
 
                                print(1.10)
 
                else :
 
                                print(‘bad choice‘)
 
                如果有默认处理情况,则通过字典的get方法
 
                例如:
 
                branch = {‘spam‘:1.25,‘ham‘:1.99,‘eggs‘:0.99,‘bacon‘:1.10}
 
                print(branch.get(‘spam‘,‘bad choice‘))
 
3、跨越多行的方法:()|{}|[]或者\(不提倡使用)或者‘‘‘  ‘‘‘  """   """
 
4、任何非零数字或者非空对象都为真,数字零,空对象,特殊对象,None都被认作是假,比较和相等测试会递归应用在数据结构中
 
5or操作,python会由左到右求算操作对象,返回第一个为真的对象,如果没有为真的对象,则返回最后一个对象。
 
                print((2 or 3), (3 or 2))  #输出:2,3
 
                print([] or 3#输出:3
 
                print([] or {})  #输出:{}
 
6and操作,python会由左向右求算操作对象,当所有的为真时,返回右边那个对象,如果遇到为假的对象,则返回第一个为假的对象
 
                print((2 and 3), (3 and  2))  #输出:3,2
 
                print([] and 3#输出:[]
 
                print([] and {})  #输出:[]
 
7if/else三元表达式
 
                if x:
 
                                a = y
 
                else:
 
                                a = z
 
                等价于:
 
                a = y if x else z
 
                等价于:
 
                a = ((x and y) or z)
 
                等价于:
 
                a = (‘z‘,‘y‘)[bool(x)]
 
8while循环,当没有执行break语句时,才执行else部分
 
                while test:
 
                                statement1
 
                else statement2
 
9、在python中有一条空语句:pass  它什么也不做
 
10for循环
 
                for target in object :
 
                                statement
 
                else
 
                                statement
 
                例如:
 
                D = {‘a‘:1,‘b‘:2,‘c‘:3}
 
                for key in D:
 
                                print(key,‘=>‘,D[key])
 
                
 
                for (key,value) in D.items():
 
                                print(key,‘=>‘,value)
 
                                
 
11range用法,range(终止),range(起始,终止),range(起始,终止,步长 )起始默认是0,步长默认是1
 
12、在python2.6map也能实现zip函数功能,但是在python3.0中不能使用
 
                例如:
 
                map(None,(‘a‘,b‘,‘c‘),(1,2,3))  #输出:[(‘a‘:1,‘b‘:2,‘c‘:3)]
 
13enumerate返回索引和该索引位置上所对应的值,该函数对字符串,列表,元组有效,对字典没有效
 
                例如:
 
                s = ‘spam‘
 
                for (i,v) in enumerate(s):
 
                                print(i,‘->‘,v)
 
                print(‘*‘*8)
 
                L = [‘a‘,‘b‘,‘c‘,‘d‘]
 
                for (i,v) in enumerate(L):
 
                                print(i,‘->‘,v)
 
                print(‘*‘*8)
 
                t = (‘a‘,‘b‘,‘c‘,‘d‘)
 
                for (i,v) in enumerate(t):
 
                                print(i,‘->‘,v)
 
                print(‘*‘*8)

  

Python中语句结构,布布扣,bubuko.com

Python中语句结构

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