Python----------file operations

First, the document processing process

1. Open the file, get the file handle and assign a value to a variable

2. Manipulating files with a handle

3. Close the file

Second, the basic operation

1. File Open mode

File handle =open (' File path ', ' mode ')

When you open a file, you specify the file path and how to open the file.

The mode of opening the file is:

• R, read-only mode "default mode, file must exist, not present, throw exception"
• W, write-only mode "unreadable; not exist" created; empty content "
• X, write-only mode "unreadable; not present, create, present error"
• A, append mode "readable; not present, create; append content only"

• ##只读模式#F=open (R ' c.txt ', encoding= ' utf-8 ')## print (' ====>1 ', F.read ())## print (' ====>2 ', F.read ())## Print (f.readable ())## Print (F.readline (), end= ")## Print (F.readline ())## print ("=" *20)## Print (F.read ())#print (F.readlines ())#f.close ()#Write mode: The file does not exist, it is created, the file exists, overwriting the original#F=open ("new.py", ' W ', encoding= ' utf-8 ')#f.write (' 1111111111\n ')#f.writelines ([' 2222\n ', ' 2222548\n ', ' 978646\n '])#f.close ()#Append mode: File does not exist then create, file exists will not overwrite, write content is appended way write#f=open (' new.py ', ' a ', encoding= ' utf-8 ')#f.write (' nishishui\n ')#f.writelines ([' aa\n ', ' bb\n '])#f.close ()

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"+" means you can read and write a file at the same time

• r+, read and write "readable, writable"
• w+, write "readable, writable"
• x+, write "readable, writable"
• A +, write "readable, writable"

"B" means to operate in bytes

• RB or R+b
• WB or W+b
• XB or W+b
• AB or A+b

Note: When opened in B, the content read is a byte type, and a byte type is required for writing, and encoding cannot be specified

Practice, using B-mode, write a CP tool that requires the following:

1. Can copy text and copy video, pictures and other files

1 #b Mode2F=open ('1.jpg','RB')3Data=F.read ()4 #print (data)5F=open ('2.jpg','WB')6 f.write (data)7 Print(data)

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Third, context management

1. With open (' A.txt ', ' W ') as F:

Pass

2.with open (' A.txt ', ' R ') as Read_f,open (' B.txt ', ' W ') as Write_f:

Data=read_f.read ()

Write_f.write (data)

Iv. Modification of documents

1 ImportOS2With open ('a.txt','R', encoding='Utf-8') as Read_f,3Open'A.txt.swap','W', encoding='Utf-8') as Write_f:4      forLineinchRead_f:5 Write_f.write (line)6 7Os.remove ('a.txt')8Os.rename ('. A.txt.swap','a.txt')

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Five, the cursor movement within the file

One: Read (3):

1. When the file is opened in text mode, the representation reads 3 characters

2. When the file is opened in B mode, the delegate reads 3 bytes

Second: The rest of the files within the cursor movement are in bytes such as Seek,tell,truncate

Attention:

1. Seek has three modes of movement 0,1,2, of which 1 and 2 must be performed in B mode, but regardless of which mode is moved in bytes units

2. Truncate is to truncate the file, so the file must be opened in a way that can be written, but cannot be opened with W or w+, because that will directly empty the file, so truncate to r+ or a or a + and other modes to test the effect

1 Import Time2With open ('Test.txt','RB') as F:3F.seek (0,2)4      whileTrue:5Line=F.readline ()6         ifLine :7             Print(Line.decode ('Utf-8'))8         Else:9Time.sleep (0.2)

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Python----------file operations