Python file manipulation methods

Objective:

• Concept of documentation
• Basic file operations
• Common operations on files/folders
• How text files are encoded

1. The concept of documentation

1.1 Concept and role of documentation

A computer file, which is a piece of data stored on some kind of long-term storage device

Long-term storage devices include: hard drives, USB drives, removable drives, CD-ROMs ----

The role of documentation:

Store data for a long time and use it when needed

1.2 How documents are stored

• In computers, files are saved on disk as binary

Text and binary files

• text file
  • It can be viewed with text editing software
  • It's still essentially binary.
  • Example: Python source file
• binary file
  • Saved content is not intended to be read directly, but is provided for use by other software
  • For example: image files, audio files, video files, etc.
  • Binary files cannot be viewed directly with a text editor

2. Basic operation of documents

2.1 Sets of manipulated documents

In computers, the routine to manipulate files is very fixed and consists of three steps:

• Open file
• Read and write files
  • Read: reads the contents of the file into memory
  • Write: Write the contents of memory to a file
• Close file

2.2 Functions/methods to manipulate files

• 1 function and 3 methods to remember to manipulate files in Python

• The open() function opens the file and returns the file object.
• The read/write/close methods all need to be called from a file object.

2.3 read method - reading a file

• The first argument to the open function is the name of the file to be opened (file names are case sensitive)
  • If the file exists, return the file operation object
  • If the file does not exist, an exception is thrown
• The read method reads and returns the entire contents of a file at once.
• The close method closes the file.
  • If you forget to close a file, it can cause a drain on system resources and can affect subsequent access to the file
• Note: After the method executes, it moves the file pointer to the end of the file
• Tip:
  • In development, it is common to write open and close code first, and target file read/write operations in the middle!

# Get the file operation object (file)
file = open("")
#Read
text = ()
print(text)
# Close the file
()
'''
Running Result
I am Chinese Oh
nidie Chinese
'''

• File Pointer File Pointer

• File pointer Marks the location from which to start reading.
• When opening a file for the first time, the file pointer will usually point to the beginning of the file
• When the read method is executed, the file pointer moves to the end of the read content
  • By default it moves to the end of the file
• Think: If you execute the read method once and read everything, can you call the read method again and still get the contents?
  • Answer: No. After the first read, the file pointer moves to the end of the file, and another call will not read any content.

File Pointer Demo

# Get the file operation object (file)
 file = open("")
 #Read
 text = ()
 # View the length of the read file (14)
 print(len(text))
 # Output the read file
 print(text)
 print("*"*30)
 #Re-read the file
 text = ()
 print(text)         # Empty
 print(len(text))    # （0）
 # Close the file
 ()
 
 """
 Run the results:
 14
 I am Chinese oh
 nidie Chinese
 ******************************

 0
 """

2.4 Ways to open a file

• The open function opens in read-only mode by default and returns the file object

The syntax is as follows:

f = open( " filename " , " access method " )

Tip: Frequent movement of the pointer will affect the efficiency of reading and writing files, and more often than not, the development of read-only, write-only way to manipulate files.

2.5 Reading file contents by line

• The read method by default reads the entire contents of the file into memory at once.
• If the file is too large, it can be a serious memory hog

readline method:

• Can read one line at a time
• method executes, it moves the pointer to the next line, ready to read again the

The correct posture for reading large files:

# Open the file
file = open("")
while True:
    #Read a line
    text = ()
    # Determine if content is read
    if text == "":          # or if not text.
        print(type(text))   #<class 'str'>
        break
    # Every time you read to the end there's a \n
    print(text,end="")
"""
Run the results:
python1 one
python2 two
python3 three
python4 four <class 'str'>
"""

2.6 File Read and Write Case - Copying Files

Objective: To implement the file copying process in code

Small file replication

Open an existing file, read the full contents, and write to another file

# Copying small files mode 1
 file_read = open("","r")
 file_write = open("","w")
 text_1 = file_read.read()
 text_2 = file_write.write(text_1)
 file_write.close()
 file_read.close()
 
 # Copy small files way 2 recommended (with keyword, will automatically free up space in file object)
 test = None
 with open("","r") as file:
     test = ()
 with open("","w") as file:
     (test)

Large File Replication

Open an existing file, read the contents line by line, and write them sequentially to another file.

# Large file duplication
 file_read = open("Five Stroke Roots","rb")
 file_write = open("Five Stroke Roots","wb")
 while True:
     text = file_read.readline()
     In #python, all conversions are True except '', "", 0, (), [], {}, and None, which are False. That is, strings are always converted to True if they are not empty.
     if not text:
         break
     file_write.write(text)
 file_read.close()
 file_write.close()

2.7 Functions in file reading and writing

file reading- Python 3.10.1 Documentation

3. Common management operations for files/directories

• In Terminal/File Browsing, you can perform regular file/directory management operations, such as

Create, rename, delete, change roadkill, view catalog contents ........

• In Python, if you want to do this programmatically, you need to import the os module

File Operations:

Catalog Operations:

Tip: File or directory operations are supportedrelative pathcap (a poem)Definitely Lugin.

4. How text files are encoded

pass

# -*- coding: utf8 -*-

# -*- coding: utf-8 -*-

# -*- coding: gbk -*-

5. Expansion: eval function

The eval function is very powerful - it evaluates a string as if it were a valid expression and returns the result.

# -*- coding: gbk -*-
#Basic math calculations
print(eval("1+1"))
#String repetition
print(eval("'*'*30"))
# Convert strings into lists
print(type(eval("[1,2,3,4,5]")))
# Convert strings into tuples
print(type(eval("(1,2,3,4,5)")))
# Convert strings into dictionaries
print(type(eval("{'name':'Apple','age':18}")))

Case - Calculator

input_str = input("Enter the math problem.")
print(eval(input_str))
'''
Run:
Enter the arithmetic problem 1+1
2
'''

Note: Never use eval to directly convert the result of input during development.

The above mentioned is a small introduction to Python file manipulation, I hope to help you. Here also very much thank you for the support of my website!