Implementation method of reading and writing txt files and json files in python

The first step is to open the file. There are two functions to choose from: open() and file()

①. f = open('file.txt', 'w')
...
file.close()

②. f = file('file.json','r')
...

file.close()# Remember to close the file at the end when opening it!

open() and file() are both built-in functions of Python. They return a file object and have the same function and can be replaced at will. The usage syntax is:

f = open(fileName, access_mode='r', buffering=-1)

The first parameter is the file name. Parameters 2 and 3 have default values. Parameter 2 determines the reading mode ‘r’? Or is it written with 'w'? Or open the file in another way.

Opening methods are:

r - read; w - write; a - append, start writing from EOF, that is, write at the end of the file

r+ w+ a+ —— They are all opened in reading and writing mode

rb - binary reading; wb - binary writing; rb+ wb+ ab+ - binary reading and writing

Example:

fp = open('C:\Users\MPC\Desktop\说明.txt')# 默认以读的方式打开

fp = open('test.txt','w')# 写方式打开

fp = open('data.json','a')#追加方式打开

The second step is to operate the file

After getting the handle of the file object (such as fp in the example), you can operate the file.

The built-in operation methods of file objects include: input, output, movement within files, and miscellaneous operations

1. Enter

Function: read(), readline(), readlines()

Read the contents of the file into a string variable/list

read(): Read the entire file into a string variable

Example:

fp = open('C:\Users\MPC\Desktop\说明.txt')

all_file = fp.read()

read() has an optional size parameter, the default is -1, which means the file will be read to the end (EOF)

readline(): Read a line in the open file, and then return the entire line including the line terminator to the string variable

readline() also has an optional parameter size, the default is -1, which means reading stops at the end of the line

readlines(): Read the entire file and return a string list. Each element in the list is a string, representing a line

Example:

fp = open('C:\Users\MPC\Desktop\说明.txt')

lines = fp.readlines()

for line in lines:

...

fp.close()

or lines 2 and 3 are abbreviated as: for line in fp.readlines():

After python2.3 due to the introduction of iterators and file iteration (i.e. file objects become their own iterators),

There is a more efficient way to implement the above example:

fp = open('C:\Users\MPC\Desktop\说明.txt')

for line in fp:

...

fp.close()

Recommended to use this method!

2. Output

Function: write(), writelines()

Output string/list to file

write(): Output string to file

>>>f= open('test.txt','w')

>>>f.write('Helloworld!')

>>>f.close()

>>>f= open('test1.txt','w')

>>>f.write('Welcome\nto\n China!')

>>>f.close()

>>>f= open('test1.txt','w')

>>>f.write('Welcome\nto\n China!')

>>>f.close()

writelines(): Write a list of strings to a file. Note that line terminators are not automatically added. If necessary, line terminators must be added manually at the end of each line.

What does it mean? Look at the example below:

>>>s= ['你好','伙计']

>>>f= open('test.txt','w')

>>>f.writelines(s)

>>>f.close()

>>>s= ['你好\n','伙计']

>>>f= open('test.txt','w')

>>>f.writelines(s)

>>>f.close()

>>>f = open(r'I:\python\test.txt','w')

>>>f.write('First line\n')

>>>f.write('Second line\n')

>>>f.write('Third line\n')

>>>f.close()

>>>lines = list(open(r'I:\python\test.txt'))

>>>lines

['Firstline\n', 'Second line\n', 'Third line\n']

>>>first,second,third = open(r'I:\python\test.txt')

>>>first

'Firstline\n'

>>>second

'Secondline\n'

>>>third

'Thirdline\n'

3. Move within files

Function: seek() tell()

seek(): Move the file reading pointer to the specified position

tell(): Returns the position of the file reading pointer

Three modes of

seek():

(1) f.seek(p,0) Move the p-th byte of the file to the absolute position

(2) f.seek(p,1) Move to p bytes after the current position

(3) f.seek(p,2) Move to p bytes after the end of the relative article

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