python第三天
集合及其运算
#集合是无序的,去重的 list_1 = [1,2,3,3,4,4,5,6] list_1 = set(list_1)#去除重复的元素 print(list_1) list_2 = set([1,55,6,4,77,64]) print(list_1,list_2) #交集 print(list_2.intersection(list_1)) print(list_1 & list_2) #并集 print(list_1.union(list_2)) print(list_2 | list_1) #差集 print(list_1.difference(list_2))#list_1中有的，list_2没有的 print(list_1 - list_2) print(list_2.difference(list_1))#list_2中有的，list_1没有的 print(list_2 - list_1) #子集 list_3 = set([1,4,6]) print(list_3.issubset(list_1)) print(list_1.issuperset(list_3)) #对称差集 print(list_1.symmetric_difference(list_2))#两方互相没有的元素 print(list_1 ^ list_2) print('--------------------------------------') list_4 = set([2,3,5]) print(list_3.isdisjoint(list_4))#判断是否存在交集，存在为F，不存在T #添加 list_1.add(999) list_1.update([888,777,666])#添加多项 print(list_1) #print(list_1.pop())#随机删除 list_1.discard(464)#不存在是不会报错
文件读与写
#data = open('yest',encoding='utf-8').read() #print(data) #读 f = open('yest','r',encoding='utf-8')# r为读模式 w为写模式 a为添加模式 data = f.read()#指针已经到达底部，所以没有数据 print(data) f.close() #写 f = open('yest2','w',encoding='utf-8') f.write('中华人民共和国\n') f.write('河北\n') f.close() #添加 f = open('yest2','a',encoding='utf-8') f.write('中华人民共和国\n') f.write('河北\n') f.close() #单行输出 f = open('yest','r',encoding='utf-8') for i in range(5): print(f.readline())#读取一行 f.close() #多行输出 f = open('yest','r',encoding='utf-8') for index,line in enumerate(f.readlines()):#读取全部组成一个列表，一行为一个元素 if index == 9: print('-----分割线------') continue print(line.strip())#数字元素中含有换行符,需要strip注释掉 f.close() #多行输出，防止内存不足，只保留一行在内存 f = open('yest','r',encoding='utf-8') count = 0 for line in f: count +=1 if count == 10: print('-----分割线------') continue print(line.strip()) f.close() #指针的操作 f = open('yest','r',encoding='utf-8') print(f.tell())#获取指针位置 print(f.readline()) print(f.readline()) print(f.readline()) print(f.tell()) f.seek(0) print(f.readline()) f.close() #其他 f = open('yest','a',encoding='utf-8') print(f.encoding)#编码格式 print(f.flush())#实时刷新，将内容保存在硬盘 f.truncate()#截断没有参数则是清零，参数截取范围 f.close() #读写 操作原文 f = open('yest','r+',encoding='utf-8') print(f.readline()) print(f.readline()) print(f.readline()) f.write('--------------------------') f.close() #写读 创建新文件 f = open('yest3','w+',encoding='utf-8') print(f.readline()) f.write('--------------------------\n') f.write('--------------------------\n') f.seek(5) print(f.readline()) f.close() #加读 除了加还可以读 f = open('yest3','a+',encoding='utf-8') f.close() #二进制文件，视频语音之类 f = open('yest3','rb') print(f.readline()) print(f.readline()) f.close() f = open('yest3','wb') f.write('hello binary\n'.encode()) f.close()
文件修改
f = open('yest2','r',encoding='utf-8') f_new = open('yest2.bak','w',encoding='utf-8') for line in f: if '河北' in line: line = line.replace('河北','河北省') f_new.write(line) f.close() f_new.close()
字符编码转换
import sys print(sys.getdefaultencoding()) #python默认Unicode编码 s = '你好' #python3默认为utf-8。与文件都无关 s_gbk = s.encode('gbk') #转成GBK print(s_gbk)#gbk print(s.encode())#utf-8 gbk_to_utf8 = s_gbk.decode('gbk').encode('utf-8') print('utf-8',gbk_to_utf8)
函数
#函数 def func1(): '''testing1''' print('in the func1') return 0 #过程 def func2(): '''testing2''' print('in the func2') x = func1() y = func2() print('from func1 return is %s'%x) print('from func2 return is %s'%y)
import time def logger(): time_format = '%Y-%m-%d %X' time_current = time.strftime(time_format) with open('a.txt','a+') as f: f.write('%s end action\n' %time_current) def test1(): print('test1 starting action...') logger() def test2(): print('test2 starting action...') logger() def test3(): print('test3 starting action...') logger() test1() test2() test3()
def test1(): print('in the test1') def test2(): print('in the test1') return 0 def test3(): print('in the test2') return 1,'hello',['zzz','aaaa']#返回一个元组 print('test end')#此句及其后面的都不会运行 x = test1() y = test2() z = test3() print(x) print(y) print(z)
def test(x,y,z): print(x) print(y) print(z) test(1,2,3) #与形参一一对应 test(z=3,y=2,x=1) #与形参顺序无关 test(1,z=3,y=2) #test(x=1,2,3)出错
def test(x,y=2): print(x) print(y) print('成功') test(1) test(1,y=3) test(1,3) #默认参数特点：调用函数的时候，默认参数非必须传递
#参数组 def test1(x,*args): print(x) print(args) #**kwargs:把N个关键字，转换成字典的方式 def test2(**kwargs): print(kwargs) print(kwargs['name']) print(kwargs['age']) print(kwargs['sex']) test1(1,2,3,4,5) test1(*[1,2,3,4,5,6]) # *args = *[1,2,3,4,5,6] test2(name='李',age=18,sex='男') test2(**{'name':'li','age':8,'sex':'男'})
局部变量和全局变量
school = '全局变量1' names = ['li','zhang','wang'] def change_name(name): global school #方法内更改全局变量需要声明 print('before change',name) name = 'LI' print('before change',name) school = '全局变量2'#如果没有声明，则为正常的局部变量 names[0] = 'lisi'#字符串，整数以外的数据类型的全局变量，可以修改 name = 'li' change_name(name) print(school) print(names)
递归
1.必须有一个明确的结束条件
2.每次进入更深一层，问题规模相比上一次应有所减少
3.递归效率不高
def calc(n): print(n) if int(n/2) > 0: return calc(int(n/2)) print('-->',n) #最大递归次数999 calc(10)
