一、python字典操作
1.字典的定义
字典一种key-value的数据类型，类似于json串。
2.字典的特性
key:value 字典不可变，key唯一
key的定义规则： 1.不可变，数字、字符串、字典、元组(定义符合()，与列表完全一致，唯一不同的是元组内元素不可变) 2.key必须是唯一的,所以字典天生有去重功能 value的定义规则： 1.任意数据类型
3.字典的使用方法
字典的增、删、改、查
1 查询: 2 print(dic[‘name‘]) 3 print(dic.get(‘name‘)) #get方法查询不存在的项不会报错 4 5 添加: 6 dic[‘gender‘] = ‘female‘ #k:v 无序添加 7 8 修改: 9 dic[‘name‘] = ‘11‘ #key不可修改 10 11 删除: 12 del #万能删除 13 del dic[‘name‘] #删除key
其他使用方法和函数调用
dicl = dict.fromkeys() #快速生成字典 dic.copy() #浅拷贝，只拷贝一层 dic.get() #值不存在不会报错 dic.items() #打印转换为列表形式 dic.keys() #取出字典中所有的key值 dic.pop() #pop删除，括号内写key，key不存在会报错 dic.popitem() #随机删除一对key.val dic.setdefault() #添加字典 dic.update() #添加新字典，添加字典内容，修改字典内容 dic.values() #取出字典所有values值
字典的定义方法
字典的定义方法：
dic = dict() #空字典
dic1 = dict({‘name‘:‘alex‘,‘age‘:18})
print(dic1)
dic2 = dict(name=‘alex‘,age=18)
print(dic2)
dic3 = dict(((‘name‘,‘alex‘),(‘age‘,‘18‘)))
print(dic3)
二、集合
1.集合的介绍
集合是一个无序的，不重复的数据组合，它的主要作用如下：
- 去重，把一个列表变成集合，就自动去重了
- 关系测试，测试两组数据之前的交集、差集、并集等关系
2.集合的操作方法
增加 add #添加元素到集合
update #添加集合到集合
随机删除 pop #随机删除
remove #指定删除，如果删除元素不存在，程序报错
discard #指定删除，如果删除元素不存在，报none
清空
clear #清空
差集并赋值
symmetric_difference_update #差集后，赋予新值
集合的几种模式
- 交集：intersection print(s1&s2) - 并集：union print(s1|s2) - 差集：difference print(s1-s2) - 子集：issubset print(s1<=s2) - 父集：issuperset print(s1>=s2) - 对称差集：symmetric_difference print(s1^s2) #去掉两个集合里重复的
三、字符编码
1.在python2默认编码是ASCII, python3里默认是utf-8
2.unicode 分为 utf-32(占4个字节),utf-16(占两个字节)，utf-8(占1-4个字节)， so utf-8就是unicode
3.在py3中encode,在转码的同时还会把string 变成bytes类型，decode在解码的同时还会把bytes变回string
4.内存固定使用Unicode编码，硬盘的编码可以修改(即可以修改的软件编码)
5.使用什么编码往硬盘存，就用什么编码去读
6.程序运行分两个阶段：
- 从硬盘读到内存
- python解释器运行读到内存里的代码
7.针对.py文件，python与nodpad++\vim的区别是多了运行已经读到内存里的代码
四、python文件处理
1.关于python循环读取数据
文本文件：
1 Somehow, it seems the love I knew was always the most destructive kind 2 不知为何，我经历的爱情总是最具毁灭性的的那种 3 Yesterday when I was young 4 昨日当我年少轻狂 5 The taste of life was sweet 6 生命的滋味是甜的 7 As rain upon my tongue 8 就如舌尖上的雨露 9 I teased at life as if it were a foolish game 10 我戏弄生命 视其为愚蠢的游戏 11 The way the evening breeze 12 就如夜晚的微风 13 May tease the candle flame 14 逗弄蜡烛的火苗 15 The thousand dreams I dreamed 16 我曾千万次梦见 17 The splendid things I planned 18 那些我计划的绚丽蓝图 19 I always built to last on weak and shifting sand 20 但我总是将之建筑在易逝的流沙上 21 I lived by night and shunned the naked light of day 22 我夜夜笙歌 逃避白昼赤裸的阳光 23 And only now I see how the time ran away 24 事到如今我才看清岁月是如何匆匆流逝 25 Yesterday when I was young 26 昨日当我年少轻狂 27 So many lovely songs were waiting to be sung 28 有那么多甜美的曲儿等我歌唱 29 So many wild pleasures lay in store for me 30 有那么多肆意的快乐等我享受 31 And so much pain my eyes refused to see 32 还有那么多痛苦 我的双眼却视而不见 33 I ran so fast that time and youth at last ran out 34 我飞快地奔走 最终时光与青春消逝殆尽 35 I never stopped to think what life was all about 36 我从未停下脚步去思考生命的意义 37 And every conversation that I can now recall 38 如今回想起的所有对话 39 Concerned itself with me and nothing else at all 40 除了和我相关的 什么都记不得了 41 The game of love I played with arrogance and pride 42 我用自负和傲慢玩着爱情的游戏 43 And every flame I lit too quickly, quickly died 44 所有我点燃的火焰都熄灭得太快 45 The friends I made all somehow seemed to slip away 46 所有我交的朋友似乎都不知不觉地离开了 47 And only now I‘m left alone to end the play, yeah 48 只剩我一个人在台上来结束这场闹剧 49 Oh, yesterday when I was young 50 噢 昨日当我年少轻狂 51 So many, many songs were waiting to be sung 52 有那么那么多甜美的曲儿等我歌唱 53 So many wild pleasures lay in store for me 54 有那么多肆意的快乐等我享受 55 And so much pain my eyes refused to see 56 还有那么多痛苦 我的双眼却视而不见 57 There are so many songs in me that won‘t be sung 58 我有太多歌曲永远不会被唱起 59 I feel the bitter taste of tears upon my tongue 60 我尝到了舌尖泪水的苦涩滋味 61 The time has come for me to pay for yesterday 62 终于到了付出代价的时间 为了昨日 63 When I was young 64 当我年少轻狂
lyrics
读取文件前5行：
#-*- coding:utf-8 -*-
data = open("lyrics",encoding=‘UTF-8‘)
##循环打印readlines,占用内存空间不推荐
for index,line in enumerate(data.readlines()):
if index < 5:
print(line)
else:
break
##循环打印readline
for i in range(5):
print(data.readline().strip())
##循环打印for
count = 0
for line in data:
if count < 5:
print(line.strip())
count +=1
else:
break
2.python文件处理命令用法
基本的文件模式
1 #r,读模式，open命令默认是读模式 2 f = open(‘testfile‘,‘r‘,encoding=‘utf-8‘) 3 print(f.read()) 4 5 #w,写模式 6 f = open(‘testfile‘,‘w‘,encoding=‘utf-8‘) 7 f.write(‘人生苦短，我学python\n‘) 8 f.close() 9 10 #a,追加模式 11 f = open(‘testfile‘,‘a‘,encoding=‘utf-8‘) 12 f.write(‘我呵呵你！\n‘) 13 f.close() 14 15 #删除，打开一个文件写入空即删除 16 f = open(‘testfile‘,‘r+‘,encoding=‘utf-8‘) 17 f.readline() 18 f.write(‘‘) 19 20 #r+,读写 可读，追加内容到最后 21 f = open(‘testfile‘,‘r+‘,encoding=‘utf-8‘) 22 f.readline() 23 f.write(‘devops\n‘) 24 25 #w+,写读 新建文件，写入再读取 26 f = open(‘testfile‘,‘w+‘,encoding=‘utf-8‘) 27 f.readline() 28 f.write(‘devops2\n‘) 29 30 # a+,追加读 清空源文件，再添加，然后读取 31 f = open(‘testfile‘,‘w+‘,encoding=‘utf-8‘) 32 f.readline() 33 f.write(‘devops3\n‘)
其他文件操作方法
f = open(‘testfile‘,‘w+‘,encoding=‘utf-8‘) f.close() f.closed #判断操作的文件是否关闭 f.encoding #打印文件的编码格式 f.fileno() #返回操作系统接口文件索引<网络编程，I/O复用> f.flush() #刷新操作 f.isatty() #判断打开的文件是否是终端文件 f.name #打印文件名 f.newlines #未读取到行分隔符时为 None,只有一种行分隔符时为一个字符串,当文件有多种类型的行结束符时,则为一个包含所有当前所遇到的行结束符的列表 f.readable() #同isatty类似 f.seek() #移动光标，到固定位置返回此位置以后的内容(按照字符移) f.tell() #打印光标所在位置的索引 f.truncate() #截断，配合seek，括号内指定保留字符数量，从头开始切 f.writelines() #写列表到文件
1 def close(self): # real signature unknown; restored from __doc__ 2 """ 3 Close the file. 4 5 A closed file cannot be used for further I/O operations. close() may be 6 called more than once without error. 7 """ 8 pass 9 10 def fileno(self, *args, **kwargs): # real signature unknown 11 """ Return the underlying file descriptor (an integer). """ 12 pass 13 14 def isatty(self, *args, **kwargs): # real signature unknown 15 """ True if the file is connected to a TTY device. """ 16 pass 17 18 def read(self, size=-1): # known case of _io.FileIO.read 19 """ 20 注意，不一定能全读回来 21 Read at most size bytes, returned as bytes. 22 23 Only makes one system call, so less data may be returned than requested. 24 In non-blocking mode, returns None if no data is available. 25 Return an empty bytes object at EOF. 26 """ 27 return "" 28 29 def readable(self, *args, **kwargs): # real signature unknown 30 """ True if file was opened in a read mode. """ 31 pass 32 33 def readall(self, *args, **kwargs): # real signature unknown 34 """ 35 Read all data from the file, returned as bytes. 36 37 In non-blocking mode, returns as much as is immediately available, 38 or None if no data is available. Return an empty bytes object at EOF. 39 """ 40 pass 41 42 def readinto(self): # real signature unknown; restored from __doc__ 43 """ Same as RawIOBase.readinto(). """ 44 pass #不要用,没人知道它是干嘛用的 45 46 def seek(self, *args, **kwargs): # real signature unknown 47 """ 48 Move to new file position and return the file position. 49 50 Argument offset is a byte count. Optional argument whence defaults to 51 SEEK_SET or 0 (offset from start of file, offset should be >= 0); other values 52 are SEEK_CUR or 1 (move relative to current position, positive or negative), 53 and SEEK_END or 2 (move relative to end of file, usually negative, although 54 many platforms allow seeking beyond the end of a file). 55 56 Note that not all file objects are seekable. 57 """ 58 pass 59 60 def seekable(self, *args, **kwargs): # real signature unknown 61 """ True if file supports random-access. """ 62 pass 63 64 def tell(self, *args, **kwargs): # real signature unknown 65 """ 66 Current file position. 67 68 Can raise OSError for non seekable files. 69 """ 70 pass 71 72 def truncate(self, *args, **kwargs): # real signature unknown 73 """ 74 Truncate the file to at most size bytes and return the truncated size. 75 76 Size defaults to the current file position, as returned by tell(). 77 The current file position is changed to the value of size. 78 """ 79 pass 80 81 def writable(self, *args, **kwargs): # real signature unknown 82 """ True if file was opened in a write mode. """ 83 pass 84 85 def write(self, *args, **kwargs): # real signature unknown 86 """ 87 Write bytes b to file, return number written. 88 89 Only makes one system call, so not all of the data may be written. 90 The number of bytes actually written is returned. In non-blocking mode, 91 returns None if the write would block. 92 """ 93 pass
python2中源码解释
时间： 2024-10-16 14:47:34