python基础3
python基础3
交换： a,b=b,a 相当于定义了一个元组t=（b,a） 然后将t[0]的值给了a，t[1]的值给了b ####字典#### 定义用花括号 集合定义若为空的话，会默认为字典，所以集合不能为空 子典只能通过关键字来查找值，因为字典是key-value（关键字-值），因此不能通过值来查找关键字 In [1]: dic = {"user1":"123","user2":"234","user3":"789"} In [3]: dic["234"] --------------------------------------------------------------------------- KeyError Traceback (most recent call last) <ipython-input-3-2845b64d96b1> in <module>() ----> 1 dic["234"] KeyError: '234' 字典是一个无序的数据类型，因此也不能进行索引和切片等操作。 In [1]: dic = {"user1":"123","user2":"234","user3":"789"} In [2]: dic["user1"] Out[2]: '123' In [5]: dic["user2"] Out[5]: '234' In [7]: user = ['user1','user2','user3'] In [8]: passwd = ['123','234','456'] In [9]: zip(user,passwd) Out[9]: [('user1', '123'), ('user2', '234'), ('user3', '456')] In [10]: 当你有一个用户名单和密码，若使用列表的类型，判断用户是否和密码一致时，就比较麻烦，而使用字典时，只需通过关键子就可以返回相对应的值，（如上例子：当定义一个子典当你搜索user1时，字典类型就会返回该关键字对应的密码，此时只需判断该密码是否匹配即可） ####字典的基本操作### In [17]: dic. dic.clear dic.items dic.pop dic.viewitems dic.copy dic.iteritems dic.popitem dic.viewkeys dic.fromkeys dic.iterkeys dic.setdefault dic.viewvalues dic.get dic.itervalues dic.update dic.has_key dic.keys dic.values 字典添加 In [12]: dic Out[12]: {'user1': '123', 'user2': '234', 'user3': '789'} In [13]: dic["westos"]='linux' In [14]: dic Out[14]: {'user1': '123', 'user2': '234', 'user3': '789', 'westos': 'linux'} In [15]: dic["hello"]='world' In [16]: dic ####由此可以看出字典是无序的，在添加时，并不会按照顺序往后添加#### Out[16]: {'hello': 'world', 'user1': '123', 'user2': '234', 'user3': '789', 'westos': 'linux'} In [17]: 字典更新 In [22]: dic Out[22]: {'hello': 'world', 'user1': '123', 'user2': '234', 'user3': '789'} In [23]: dic["user1"]="redhat" ###可直接通过赋值对关键字进行更新### In [24]: dic Out[24]: {'hello': 'world', 'user1': 'redhat', 'user2': '234', 'user3': '789'} ###或者通过dic.update更新### In [25]: dic Out[25]: {'hello': 'world', 'user1': 'redhat', 'user2': '234', 'user3': '789'} In [26]: help(dic.update) Help on built-in function update: update(...) D.update([E, ]**F) -> None. Update D from dict/iterable E and F. If E present and has a .keys() method, does: for k in E: D[k] = E[k] If E present and lacks .keys() method, does: for (k, v) in E: D[k] = v In either case, this is followed by: for k in F: D[k] = F[k] (END) In [28]: dic1={'yunwei':"westos",'user1': 'redhat'} In [29]: dic.update(dic) dic dic1 dict In [29]: dic.update(dic1) ###将dic1中dic所没有的更新给了dic### In [30]: dic Out[30]: {'hello': 'world', 'user1': 'redhat', 'user2': '234', 'user3': '789', 'yunwei': 'westos'} In [31]: ####若是关键字相同，而值不同，就将值更新给他#### In [35]: dic Out[35]: {'hello': 'world'} In [36]: dic1 Out[36]: {'user1': 'redhat', 'yunwei': 'westos'} In [37]: dic1["hello"]="hai" In [38]: dic.update(dic1) In [39]: dic Out[39]: {'hello': 'hai', 'user1': 'redhat', 'yunwei': 'westos'} In [42]: dic.clear() ###清空dic### In [43]: dic Out[43]: {} In [44]: del(dic) ###删除dic### In [45]: dic --------------------------------------------------------------------------- NameError Traceback (most recent call last) <ipython-input-45-1b445b6ea935> in <module>() ----> 1 dic NameError: name 'dic' is not defined ####字典的删除#### In [49]: dic1 Out[49]: {'user1': 'redhat', 'yunwei': 'westos'} In [50]: dic1.pop("user1") ###指定关键字，删除该关键字和值#### Out[50]: 'redhat' In [51]: dic1 Out[51]: {'yunwei': 'westos'} In [52]: In [74]: dic1.popitem() ###不指定关键字，随即删除### Out[74]: ('yunwei', 'westos') In [77]: dic = {"hello":"123","westos":"linux"} In [79]: dic.keys() ###查看dic的全部关键字### Out[79]: ['hello', 'westos'] In [80]: dic.values() ###查看dic的全部值### Out[80]: ['123', 'linux'] In [82]: dic.get("hello") ###得到相对应的关键字的值，若关键字不存在，则默认返回none Out[82]: '123' In [83]: dic.get("redhat") In [84]: print dic.get("redhat") None In [87]: dic.has_key("hello") ###查看是否有该关键字， Out[87]: True In [88]: dic.has_key("world") Out[88]: False dict.fromkeys() ###可以通过该操作实现去重### In [89]: dic Out[89]: {'hello': '123', 'westos': 'linux'} In [90]: dic.fromkeys([1,2,3,4]) Out[90]: {1: None, 2: None, 3: None, 4: None} In [91]: dic.fromkeys([1,2,3,4],'hello') Out[91]: {1: 'hello', 2: 'hello', 3: 'hello', 4: 'hello'} In [38]: d = {} In [32]: li = [1,2,3,1,2,3] ###去重### In [33]: d.fromkeys(li) Out[33]: {1: None, 2: None, 3: None} In [34]: d.fromkeys(li).keys() Out[34]: [1, 2, 3] 字典的key必须是不可变的数据类型 In [94]: dic = {1:'1',2:'2',1:'a'} In [95]: dic Out[95]: {1: 'a', 2: '2'} ###一个关键字只能对应一个值### In [96]: for key in dic.keys(): ###逐个遍历key### ....: print "key=%s" % key ....: key=1 key=2 In [97]: for value in dic.values(): ###逐个遍历value的值### print "value=%s" % value ....: value=a value=2 In [98]: for key,value in dic.keys(),dic.values(): ###逐个遍历key -> value 的值##### ....: print "%s -> %s" %(key,value) ....: 1 -> 2 a -> 2 In [100]: dic Out[100]: {1: 'a', 2: '2'} In [101]: dic.items() ###以元组的形式一一对应key和value的值### Out[101]: [(1, 'a'), (2, '2')] In [102]: for k,v in dic.items(): .....: print "%s -> %s" %(k,v) .....: 1 -> a 2 -> 2 和list的比较，dict的不同： 1 查找和插入的速度快，字典不会随着key值的增加查找速度减慢 2 占用内存大，浪费空间 小练习： 去掉一个最高分和最低分，并且显示平均值 li = [90,91,67,100,89] In [103]: li = [90,91,67,100,89] In [104]: li.sort() ###排序### In [105]: li Out[105]: [67, 89, 90, 91, 100] In [106]: li.pop() Out[106]: 100 In [107]: li.pop(0) Out[107]: 67 In [108]: li Out[108]: [89, 90, 91] In [109]: sum(li)/len(li) ###sum函数求和### Out[109]: 90 小练习：用字典实现case语句： !/usr/bin/env python #coding:utf-8 from __future__ import division num1 = input("num1:") oper = raw_input('操作：') num2 = input('num2:') dic = {"+":num1+num2,"-":num1-num2,"*":num1*num2,'/':num1/num2} if oper in dic.keys(): print dic[oper] #####函数#### 函数名的理解：函数名与变量名类似,其实就是指向一个函数对象的引用; 给这个函数起了一个“别名”:函数名赋给一个变量 In [5]: sum(li) Out[5]: 6 In [6]: a = sum ###将sum的函数名给了a变量，使得a能够进行求和### In [7]: a(li) Out[7]: 6 In [8]: In [8]: sum = abs In [9]: sum(-1) Out[9]: 1 In [10]: sum([2,4,5] ###将abs的函数名给了sum，则sum就不再具有求和的功能### --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-10-d3c81a94a2a0> in <module>() ----> 1 sum([2,4,5]) TypeError: bad operand type for abs(): 'list' In [11]: a([2,4,5]) Out[11]: 11 ####函数的返回值### def hello(): print "hello" print hello() ###该函数没有返回值，只是打印了hello，返回值为none def hello(): return ”hello“ print hello() ###该函数有返回值，则返回一个hello### ####函数在执行过程中一旦遇到return，就执行完毕并且将结果返回，如果没有遇到return，返回值为none### ###定义一个什么也不做的空函数，可以用pass语句，作为一个占位符使得代码先运行起来 def hello(): return "hello" def world(): pass print hello() print world() 运行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/10.py hello None Process finished with exit code 0 小练习：将abs的错误显示进行优化### def my_abs(x): if isinstance(x,(int,float)): ###判断数据类型，是int或是float(也可以是别的类型，看你写的)### print abs(x) else: print "请输入整型或浮点型的数" my_abs("a") my_abs(123) 执行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/11.py 请输入整型或浮点型的数 123 Process finished with exit code 0 小练习：定义一个函数func(name),该函数效果如下： func('hello') -> 'Hello' func('World') -> 'World' def func(name): print name.capitalize() name = raw_input("name:") func(name) 执行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/12.py name:hello Hello Process finished with exit code 0 函数的返回值，函数可以返回多个值 小练习:定义一个函数func，传入两个数字，返回两个数字的最大值和平均值 def func(x,y): if x>y: return x,(x+y)/2 else: return y,(x+y)/2 x=6 y=3 print func(x,y) 执行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/13.py (6, 4) ###由此可见，返回多个值，实际上是返回一个元组### Process finished with exit code 0 ###返回的元组的括号可以省略，函数调用接受返回值时，按照位置赋值变量### def func(x,y): if x>y: return x,(x+y)/2 else: return y,(x+y)/2 x=6 y=3 avg,maxnum = func(x,y) print avg,maxnum 执行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/13.py 6 4 Process finished with exit code 0 ###函数的参数### def power(x,n=2): ###设定n默认为2,则n为默认参数，x为必选参数### return x**n print power(2) def power(x,n=2): return x**n print power(2,4) ###也可以进行多次操作### ####当默认参数和必选参数同时存在时，一定要将必选参数放在默认参数之前### ###设置默认参数时，把变化大的参数放前面，变化小的参数放后面，将变化小的参数设置为默认参数### def enroll(name,age=22,myclass="westoslinux"): print 'name=%s'% name print 'age:%d'% age print 'class:%s' %myclass enroll('user1') enroll('user2',20) enroll('user3',18,'全能班') 执行结果： name=user1 age:22 class:westoslinux name=user2 age:20 class:westoslinux name=user3 age:18 class:全能班 Process finished with exit code 0 ###默认参数必须使不可变的数据类型### 例： 先定义一个函数,传入一个 list,添加一个END 再返回 def fun(li=[]): li.append("END") return li print fun([1,2,3]) print fun() print fun() 执行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/14.py [1, 2, 3, 'END'] ['END'] ['END', 'END'] ###因为列表是可变的数据类型，所以在第二次输入print fun()时，默认参数就不是空，而已经有了一个“END”### Process finished with exit code 0 更改为：li=None，则此时li的默认值为不可变的数据类型 def fun(li=None): if li is None: return ['END'] li.append('END') return li print fun([1,2,3]) print fun() print fun() 执行结果为： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/14.py [1, 2, 3, 'END'] ['END'] ['END'] Process finished with exit code 0 ####可变参数### 定义参数时，形参可以为*args，使函数可与接受多个参数； 如果想要将一个列表或者元组传入参数，也可以通过*li或*t，将参数传入函数里。 def fun(*args): ###参数前面一定要加*### print type(args) return max(args),min(args) li = [1,42,3,14,58,6] print fun(*li) ###传递列表时，前面也要加*### 执行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/14.py <type 'tuple'> (58, 1) Process finished with exit code 0 ###若传递列表时，不加*号### def fun(*args): print type(args) return max(args),min(args) li = [1,42,3,14,58,6] print fun(li) 执行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/14.py <type 'tuple'> ([1, 42, 3, 14, 58, 6], [1, 42, 3, 14, 58, 6]) Process finished with exit code 0 ###传递多个数### def fun(*args): print type(args) return max(args),min(args) print fun(1,42,3,14,58,6) 执行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/14.py <type 'tuple'> (58, 1) Process finished with exit code 0 ###关键字可变参数### def enroll(name,age=22,**kwargs): print 'name=%s'% name print 'age:%d'% age for k,w in kwargs.items(): print '%s:%s'%(k,w) print type(kwargs) enroll('user3',myclass='运维班') 执行结果： /usr/bin/python2.7 /home/kiosk/PycharmProjects/pythonbasic/14.py name=user3 age:22 myclass:运维班 <type 'dict'> Process finished with exit code 0 参数定义优先级：必选参数>默认参数>可变参数>关键字参数 *arg，可变参数接受的是元组 **kwargs，关键字参数，接受的是字典 ###局部变量，只在函数内部生效，全局变量，在整个代码中生效###