Catalog

File read and write  

Read the file

IOError exception handling

UnicodeDecodeError exception handling

Writing documents

File operation method

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File read and write  

        The function of reading and writing files on disk is provided by the operating system , The modern operating system does not allow ordinary programs to operate the disk directly , therefore , To read and write a file is to ask the operating system to open a file object （ Usually called a file descriptor ）, then , Read data from this file object through the interface provided by the operating system （ Reading documents ）, Or write the data to the file object （ Writing documents ）.

Read the file

Use Python Built in open() function , Pass in the filename and identifier , identifier 'r' Express reading .

f=open('F:\eclipse\eclipse\sy9T3.txt','r')

If the file does not exist, it will throw FileNotFoundError.

After successfully opening the file , call read() Methods read all the contents of the document at one time .

f.read();

Last call close() Method to close the file. The file must be closed after use , Because file objects take up operating system resources , And the operating system can open a limited number of files at the same time .

f.close()

In order to avoid too much content , Call again and again read(size) Method , Read at most each time size Bytes of content .

among readline() You can read one line at a time , call readlines() Read everything at once and return... By line list.

IOError exception handling

Because it is possible to produce IOError, Once the error , hinder f.close() Will not call . therefore , In order to ensure that the file can be closed correctly whether there is an error or not , We handle exceptions in advance ：

Method 1 ：

try...finally

try:
f = open('/path/to/file', 'r')
print(f.read())
finally:
if f:
f.close()

Method 2 ：

introduce with

with open('/path/to/file', 'r') as f:
print(f.read())

  The second method is more concise , And you don't have to call f.close() Method .

UnicodeDecodeError exception handling

read（） May throw UnicodeDecodeError(encoding No matter how it is used utf8、gb2312、gbk The coding method is not good )

terms of settlement :

Read in binary mode instead ：open('xxx.xsl','rb')

​f=open('F:\eclipse\eclipse\sy9T3.txt','rb')
f.read()

Writing documents

Writing a file is the same as reading a file , The only difference is to call open() Function time , Passed in identifier 'w' perhaps 'wb' To write a text file or binary file ：

f=open('F:\eclipse\eclipse\sy.txt','w')
f.write("I love Python!")
f.close()

After the above operations , Click open file

notes ：1. Only a call close() When the method is used , Only the operating system can ensure that all the data not written is written to the disk .

       2. With 'w' When mode writes to a file , If the file already exists , Will directly cover （ Equivalent to deleting and writing a new file ）.

You can pass in 'a' To add （append） Mode writing   Append to end of file

f=open('F:\eclipse\eclipse\sy.txt','a')
f.write("end")
f.close()

File operation method

Method effect r Open the file as read-only （ The default value is , It can be omitted ）, The file does not exist w Open the file as write only , When the file does not exist , Create file , When the file exists, the original file will be cleared ;x When the file does not exist, create a new file and write , If the file exists, an error will be reported a If the file exists , Add write content at the end of the file + Open file for update , Both readable , It can also be written , Not to be used alone , It needs to be used with other characters