Six, Python IO and anomalies 1, open (buffer) file, read file

1, open (buffer) file, read the file

1) File Mode

mode	significance
r	Read-only mode
w	Write Mode
a	Append mode
+	Write (update) mode, used in combination with other modes. R + representatives such as read-write mode, w + also represents the read-write mode (w empty file mode, the actual unreadable)
b	Binary mode can be used in conjunction with other modes. For example rb represents a binary read-only mode, rb + represent a binary read-write mode, ab append mode representing a binary

Here Insert Picture Description
Analysis :

w only represent write mode, and w + represents the read-write mode, but the actual use, the difference is not large, because the file was cleared.
r r + mode or open a file, the file itself is a requirement exists, they can not create the file.
Using w, w +, a, a + mode opens the file, the file can not exist, open () function will automatically create a new file.
b mode may be added to the other mode for reading and writing files representing a binary content (if b is not specified mode to read and write files character unit; b if specified pattern, in units of bytes to read and write files (The computer does not read the file in units of bits, a byte is 8 bits))

2) open () to open the file and read () to read the file

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

Description : open () function of the third parameter buffering control buffer

Is negative, the system default buffer size;
Is 0 or False, not buffered;
Value of 1 or True, will buffer (recommended, then program execution I / O has better performance);
Value is an integer greater than 1, as a buffer size.

(1) create a data.txt file:

Here Insert Picture Description

(2) read by character

Description :

B mode without open the file, the file is treated as a character stream, each time a character is read
open () function total default character set according to the current operating system to read the contents of the file ( see the current operating system character set )

Call read (n) method reads n characters

f = open('data.txt', 'r', True)

data1 = f.read(1)
print(data1)
print('-'*30)

data2 = f.read(2)
print(data2)

f.close()    # 关闭文件

第
------------------------------
一行

analysis:

data.txt file as GBK character set encoding (the current operating system code is GBK)
read (1) -> read (2) file pointer

Call the read () method all the contents of the file

f = open('data.txt', 'r', True)

data = f.read()
print(data)

f.close()

第一行
第二行
第三行

Analysis : open () function by default character set of the current operating system to read the contents of the file, is apt to cause an exception, resolve as follows.

Call open () function to specify the character set to open a file

f = open('data.txt', 'r', True, 'GBK')
print(f.read())
f.close()

第一行
第二行
第三行

open () function reads the file in binary manner, and to specify the character set byte data recovery (see below)

(3) read byte

Description : Open file b mode, then the file is treated as a binary stream, one byte per read

Call Read (n) method reads n bytes

f = open('data.txt', 'rb', True)

data1 = f.read(2)
print(data1, data1.decode('GBK'))    # 字节串，GBK 解码
print('-'*40)

data2 = f.read(4)
print(data2, data2.decode('GBK'))

f.close()

b'\xb5\xda' 第
----------------------------------------
b'\xd2\xbb\xd0\xd0' 一行

Call the read () method all the contents of the file

f = open('data.txt', 'rb', True)

data = f.read()
print(data)
print('-'*50)
print(data.decode('GBK'))

f.close()

b'\xb5\xda\xd2\xbb\xd0\xd0\r\n\xb5\xda\xb6\xfe\xd0\xd0\r\n\xb5\xda\xc8\xfd\xd0\xd0\r\n'
--------------------------------------------------
第一行
第二行
第三行

Analysis :

GBK character set encoding each character occupies 2 bytes
rb mode read files, can be used to handle any file content, such as pictures, music, video and other formats

3) read a text file by line

（1）readline([n])和readlines()

readline ([n]): read the contents of a line, if the parameter n specifies only reads n characters in this line

try:
    f = open('data.txt', 'r', True, 'gbk')
    while True:
        line = f.readline()      # 读取一行内容
        if not line:  
            break
        print(line, end='')
except:
     print('出现异常')
finally:
    if 'f' in globals():
        f.close()

第一行
第二行
第三行

readlines (): read all the lines in the file

try:
    f = open('data.txt', 'r', True, 'gbk')
    line = f.readlines()         # 读取所有行，返回所有行组成的列表
    print(line)
except:
     print('出现异常')
finally:
    if 'f' in globals():
        f.close()

['第一行\n', '第二行\n', '第三行\n']

(2) use an iterator to read the file

try:
    f = open('data.txt', 'r', True, 'gbk')
    for line in f:           # 文件对象本身可迭代，直接用 for-in 循环即可
        print(line, end='')
except:
     print('出现异常')
finally:
    if 'f' in globals():
        f.close()

第一行
第二行
第三行

(3) using the specified row read linecache

Description : linecache module allows to read from a specified row Python source file and stored in the internal cache optimization used. Since the main module is designed to read the source file Python (Python source file in UTF-8 character set is stored), so that the other module file in UTF-8 character set is stored can be read.

# -*- coding:utf-8 -*-
# @Time    : 2019/7/5 10:20
# @Author  : wangkai
# @File    : test.py

import linecache
import random

print(linecache.getline(random.__file__, 3), end='')    # 读取random模块的源文件的第3行
print('-'*30)

print(linecache.getline('test.py', 2), end='')    # 读取本程序的第2行

    integers
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# @Time    : 2019/7/5 10:20