17. File operations in Python

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1. File operation

• open() function
• fileinput operation file

(1), open() function

Use the open() function to open the file, and use the relevant read/write file content for the program to process and use, and the file can also be regarded as a data type in Python.

The prototype of the open() function is as follows:

• open(file, mode=’r’, buffering=’-1’, encoding=None, errors=None, newline=None, closefd=True, opener=None)

The parameters of the open() function are described as follows:

filename	filename to open
mode	optional parameter, file open mode
bufsize	optional parameter, buffer size
encoding	file encoding type
errors	Coding error handling method
newline	Controls the behavior of passing newline patterns
closefd	Controls whether the file is closed cleanly when the file is closed

mode is the operation mode string for opening the file. Common mode strings are as follows:

pattern character	indicated operation
r	read only (r)
w	Write only, will clear the file content
a	Additional data
b	binary data pattern
x	Create a new file, writable
+	Open file for direct update
t	text mode (default)

Common file operations and their functions are described as follows:

file operations	Function description
file.read([n])	Read the entire file into a string, or specify n bytes
file.readline([n])	Read a line of a file into a string
file.readlines()	Read the entire file line by line into a list
file.write(s)	write string to file
file.writelines(lines)	Write a list of line data to the file
file.close()	close open files

Example of file reading and writing:
① Use for loop to read and write

file = open('G:\\work\\python\\ClassTest.py', encoding='utf-8')
for line in file.readlines():
    print(line, end='')
file.close()

②Use while loop to read and write

file = open('G:\\work\\python\\ClassTest.py', encoding='utf-8')
while True:
    line = file.readline()
    if not line:
        break;
    print(line, end='')
file.close()

③Use the with statement to read and write

with file as f:
        for lines in f:
            print(lines, end='')

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(2), fileinput operation file

The fileinput module provides a loop to process the content of one or more files in line mode; it implements lazy iteration over the lines in the file, and does not need to put the file content into memory when reading, which improves program efficiency;

The commonly used functions of the fileinput module are:

• input() : Returns an object used to iterate over all lines in one or more files;
• filename() : returns the name of the current file;
• lineno() : returns the number of lines currently read;
• isfirstline() : Returns whether the current line is the first line of the file;
• filelineno() : Returns the number of lines currently read in the file.

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2. Common file and directory operations

(1), get the current path

import os
os.getcwd()

(2), get the contents of the directory

import os
os.listdir(path)

(3), create a directory

import os
os.mkdir(path)

(4), delete the directory

import os
os.rmdir(path)

(5), determine whether it is a directory or a file

import os
os.path.isdir(path)
ps.path.isfile(path)

(6), traverse all files and directories under the directory

import os
os.walk(path)
for i in os.walk('.\\'):
    print(i)

os.walk() returns multiple tuples; the first item is the traversed directory name, the second item is the traversed subdirectory list, and the third item is the traversed list of all files

Running result:
('G:\work\python', ['01Python crawler foundation', 'bao', ' pycache ', 'article'], ['ClassTest.py', 'compilePy.py', 'ExpectTest.py' ', 'Html.html', 'ItorTest.py', 'lambdaTest.py', 'MyPyModel.py', 'MyTestPy.py', 'MyTestPy.pyc', 'PrintTest.py', 'py10.py', 'PythonClassTest.py', 'PythonEmail.py', 'PythonImport.py', 'Test.py', 'Test20180222.py'])
('G:\work\python\01Python Crawler Basics', [], [' baiduHtmlGet.py', 'BaiduIndex.html', 'BaiduSearchHtmlIndex.html', 'BaiduSearchIndex.py', 'postTest.py', 'PostTestIndex.html', 'qbHtmlIndex.html', 'qbHtmlIndexGet.py', 'Supporting information Download address.jpg', 'Zero Basic Quick Start Python Web Crawler.ppt'])
('G:\work\python\bao', [' pycache '], ['MyPyModel.py', ' init .py'] )
('G:\work\python\bao\__pycache__', [], ['MyPyModel.cpython-36.pyc', 'init .cpython-36.pyc'])
('G:\work\python\__pycache__', [], ['ClassTest.cpython-36.pyc', 'MyPyModel.cpython-36.pyc'])
('G :\work\python\article', [], ['Python.md', 'package.md', 'exception.md', 'module.md', 'generator.md', 'iterator. md'])