Detailed explanation of Python file operations
This article mainly introduces the detailed explanation and examples of Python file operations. I hope that through this article, everyone can understand and master the knowledge of Python file operations. Friends in need can refer to
Python files Detailed explanation and examples of operations
1. File operations
1. File operation process
Open the file , get the file handle and assign it to a variable
Operation on the file through the handle
Close the file
The existing files are as follows:
昨夜寒蛩不住鸣。 惊回千里梦,已三更。 起来独自绕阶行。 人悄悄,帘外月胧明。 白首为功名,旧山松竹老,阻归程。 欲将心事付瑶琴。 知音少,弦断有谁听。 f = open('小重山') #打开文件 data=f.read()#获取文件内容 f.close() #关闭文件
Note: if in the win, the hello file is saved in utf8, and the open function is passed through the operating system when opening the file. Open the file, and the default encoding of the win operating system is gbk, so opening it directly will cause garbled characters. You need f=open('hello', encoding='utf8'). If the hello file is saved in gbk, you can open it directly.
2. File opening mode
Character Meaning
##
'r' open for reading (default) 'w' open for writing, truncating the file first 'x' create a new file and open it for writing 'a' open for writing, appending to the end of the file if it exists 'b' binary mode 't' text mode (default) '+' open a disk file for updating (reading and writing) 'U' universal newline mode (deprecated)First introduce the three most basic modes:
# f = open('小重山2','w') #打开文件 # f = open('小重山2','a') #打开文件 # f.write('莫等闲1\n') # f.write('白了少年头2\n') # f.write('空悲切!3')
3. Specific file operations
f = open('小重山') #打开文件 # data1=f.read()#获取文件内容 # data2=f.read()#获取文件内容 # # print(data1) # print('...',data2) # data=f.read(5)#获取文件内容 # data=f.readline() # data=f.readline() # print(f.__iter__().__next__()) # for i in range(5): # print(f.readline()) # data=f.readlines() # for line in f.readlines(): # print(line) # 问题来了:打印所有行,另外第3行后面加上:'end 3' # for index,line in enumerate(f.readlines()): # if index==2: # line=''.join([line.strip(),'end 3']) # print(line.strip()) #切记:以后我们一定都用下面这种 # count=0 # for line in f: # if count==3: # line=''.join([line.strip(),'end 3']) # print(line.strip()) # count+=1 # print(f.tell()) # print(f.readline()) # print(f.tell())#tell对于英文字符就是占一个,中文字符占三个,区分与read()的不同. # print(f.read(5))#一个中文占三个字符 # print(f.tell()) # f.seek(0) # print(f.read(6))#read后不管是中文字符还是英文字符,都统一算一个单位,read(6),此刻就读了6个中文字符 #terminal上操作: f = open('小重山2','w') # f.write('hello \n') # f.flush() # f.write('world') # 应用:进度条 # import time,sys # for i in range(30): # sys.stdout.write("*") # # sys.stdout.flush() # time.sleep(0.1) # f = open('小重山2','w') # f.truncate()#全部截断 # f.truncate(5)#全部截断 # print(f.isatty()) # print(f.seekable()) # print(f.readable()) f.close() #关闭文件Next we continue to expand the file mode :
# f = open('小重山2','w') #打开文件 # f = open('小重山2','a') #打开文件 # f.write('莫等闲1\n') # f.write('白了少年头2\n') # f.write('空悲切!3') # f.close() #r+,w+模式 # f = open('小重山2','r+') #以读写模式打开文件 # print(f.read(5))#可读 # f.write('hello') # print('------') # print(f.read()) # f = open('小重山2','w+') #以写读模式打开文件 # print(f.read(5))#什么都没有,因为先格式化了文本 # f.write('hello alex') # print(f.read())#还是read不到 # f.seek(0) # print(f.read()) #w+与a+的区别在于是否在开始覆盖整个文件 # ok,重点来了,我要给文本第三行后面加一行内容:'hello 岳飞!' # 有同学说,前面不是做过修改了吗? 大哥,刚才是修改内容后print,现在是对文件进行修改!!! # f = open('小重山2','r+') #以写读模式打开文件 # f.readline() # f.readline() # f.readline() # print(f.tell()) # f.write('hello 岳飞') # f.close() # 和想的不一样,不管事!那涉及到文件修改怎么办呢? # f_read = open('小重山','r') #以写读模式打开文件 # f_write = open('小重山_back','w') #以写读模式打开文件 # count=0 # for line in f_read: # if count==3: # f_write.write('hello,岳飞\n') # # else: # f_write.write(line) # another way: # if count==3: # # line='hello,岳飞2\n' # f_write.write(line) # count+=1 # #二进制模式 # f = open('小重山2','wb') #以二进制的形式读文件 # # f = open('小重山2','wb') #以二进制的形式写文件 # f.write('hello alvin!'.encode())#b'hello alvin!'就是一个二进制格式的数据,只是为了观看,没有显示成010101的形式Note 1: Whether it is py2 or py3, equal byte replacement can be done in r+ mode, but it does not make any sense!
Supplement: rb mode and seek
##
#昨夜寒蛩不住鸣. f = open('test','r',) #以写读模式打开文件 f.read(3) # f.seek(3) # print f.read(3) # 夜 # f.seek(3,1) # print f.read(3) # 寒 # f.seek(-4,2) # print f.read(3) # 鸣
In py3 :
# test: 昨夜寒蛩不住鸣. f = open('test','rb',) #以写读模式打开文件 f.read(3) # f.seek(3) # print(f.read(3)) # b'\xe5\xa4\x9c' # f.seek(3,1) # print(f.read(3)) # b'\xe5\xaf\x92' # f.seek(-4,2) # print(f.read(3)) # b'\xe9\xb8\xa3' #总结: 在py3中,如果你想要字符数据,即用于观看的,则用r模式,这样我f.read到的数据是一个经过decode的 # unicode数据; 但是如果这个数据我并不需要看,而只是用于传输,比如文件上传,那么我并不需要decode # 直接传送bytes就好了,所以这个时候用rb模式. # 在py3中,有一条严格的线区分着bytes和unicode,比如seek的用法,在py2和py3里都是一个个字节的seek, # 但在py3里你就必须声明好了f的类型是rb,不允许再模糊. #建议: 以后再读写文件的时候直接用rb模式,需要decode的时候仔显示地去解码.
4. With statement
In order to avoid forgetting to close the file after opening it, you can manage the context, that is:
with open('log','r') as f: pass
In this way, when the with code block is executed, the file resources will be automatically closed and released internally.
After Python 2.7, with supports managing the context of multiple files at the same time, that is:
with open('log1') as obj1, open('log2') as obj2: pass2
The above is the detailed content of Detailed explanation of Python file operations. For more information, please follow other related articles on the PHP Chinese website!

The basic syntax for Python list slicing is list[start:stop:step]. 1.start is the first element index included, 2.stop is the first element index excluded, and 3.step determines the step size between elements. Slices are not only used to extract data, but also to modify and invert lists.

Listsoutperformarraysin:1)dynamicsizingandfrequentinsertions/deletions,2)storingheterogeneousdata,and3)memoryefficiencyforsparsedata,butmayhaveslightperformancecostsincertainoperations.

ToconvertaPythonarraytoalist,usethelist()constructororageneratorexpression.1)Importthearraymoduleandcreateanarray.2)Uselist(arr)or[xforxinarr]toconvertittoalist,consideringperformanceandmemoryefficiencyforlargedatasets.

ChoosearraysoverlistsinPythonforbetterperformanceandmemoryefficiencyinspecificscenarios.1)Largenumericaldatasets:Arraysreducememoryusage.2)Performance-criticaloperations:Arraysofferspeedboostsfortaskslikeappendingorsearching.3)Typesafety:Arraysenforc

In Python, you can use for loops, enumerate and list comprehensions to traverse lists; in Java, you can use traditional for loops and enhanced for loops to traverse arrays. 1. Python list traversal methods include: for loop, enumerate and list comprehension. 2. Java array traversal methods include: traditional for loop and enhanced for loop.

The article discusses Python's new "match" statement introduced in version 3.10, which serves as an equivalent to switch statements in other languages. It enhances code readability and offers performance benefits over traditional if-elif-el

Exception Groups in Python 3.11 allow handling multiple exceptions simultaneously, improving error management in concurrent scenarios and complex operations.

Function annotations in Python add metadata to functions for type checking, documentation, and IDE support. They enhance code readability, maintenance, and are crucial in API development, data science, and library creation.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Dreamweaver CS6
Visual web development tools

EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function

DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software

MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

Safe Exam Browser
Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.
