Python full stack development "seventh" python file operation

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

R mode, default mode, file does not exist error

W mode, file does not exist then created, file exists overwrite

A mode, the file does not exist is created, the file is not overwritten, the content will be written in an additional way (write log file when used), append mode is a special write mode

B (rb,wb,ab) mode: Do not add encoding:utf-8

F=open (' c.txt ', ' RB ') # Print (F.read ()) print (F.read (). Decode ()) F=open (' D.txt ', ' WB ') f.write (' Cheer '. Encode (' Utf-8 ')) F.close ()

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 () #写模式: file does not exist then create, file exists overwrite 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 to write # F=open (' new.py ', ' A ', encoding= ' Utf-8 ') # f.write (' nishishui\n ') # f.writelines ([' aa\n ', ' bb\n ']) # f.close ()

"+" 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

# b Mode F=open (' 1.jpg ', ' RB ') Data=f.read () # Print (data) f=open (' 2.jpg ', ' WB ') f.write (data) print (data)

Third, context management

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

Import Oswith Open (' A.txt ', ' R ', encoding= ' Utf-8 ') as Read_f,        open (' A.txt.swap ', ' W ', encoding= ' Utf-8 ') as Write_f:    for the Read_f:        write_f.write (line) os.remove (' A.txt ') os.rename ('. A.txt.swap ', ' a.txt ')

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

Seek controls the movement of the cursor as a reference to the beginning of the file.

Tell the position of the current cursor

2. Truncate is truncated file, truncation must be write mode, but can not 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

Import Timewith Open (' test.txt ', ' RB ') as F:    F.seek (0,2) while    True:        line=f.readline ()        if line:            Print (Line.decode (' Utf-8 '))        else:            time.sleep (0.2)

　　

　　

Python full stack development "seventh" python file operation