python 文件IO

打开文件的两种方式

1.直接打开文件并赋值给变量，打开后得到操作句柄，但不会自动关闭

• file = open('文件名‘,'打开模式'，’编码‘）

• fd = open('../config/file1.txt','r',encoding='utf-8')

2.使用with子句，打开后文件会自动关闭，建议使用，并可以同时打开多个文件

with open('../config/file1.txt','r',encoding='utf-8') as fd1,
    open('../config/file2.txt','r',encoding='utf-8') as fd2:
    print("I had open two files")

 打开文件的8种模式

    ========= ===============================================================
    Character Meaning
    --------- ---------------------------------------------------------------
    'r'       open for reading (default)
    'w'       open for writing, truncating the file first
    'x'       create a new file and open it for writing
    'a'       open for writing, appending to the end of the file if it exists
    'b'       binary mode
    't'       text mode (default)
    '+'       open a disk file for updating (reading and writing)
    'U'       universal newline mode (deprecated)
    ========= ===============================================================

1.’r'，默认模式，参数可以不写，打开只读文件，写入报错

>>> fd = open('../config/file1.txt','r',encoding='utf-8')
>>> fd.write('java c rubby')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
io.UnsupportedOperation: not writable

2.‘w’，先truncate原文件，后写入，不可读，文件不存在则创建

>>> fd = open('../config/file1.txt','w',encoding='utf-8')
>>> print(fd.read())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
io.UnsupportedOperation: not readable
>>> fd.write('java rubby go')
13
>>> fd.close()
>>> fd = open('../config/file1.txt','r',encoding='utf-8')
>>> fd.read()
'java rubby go'

3.'x'，创建新文件，打开并写入，如果文件已经存在，则报错

>>> fd = open('../config/file21.txt','x',encoding='utf-8' )
>>> fd.read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
io.UnsupportedOperation: not readable
>>> fd.write('123456')
6
>>> fd.close()
>>> fd = open('../config/file21.txt','r',encoding='utf-8')
>>> fd.read()
'123456'
>>> fd.close()
>>> fd = open('../config/file21.txt','x',encoding='utf-8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
FileExistsError: [Errno 17] File exists: '../config/file21.txt'

4.’a'，追加写内容到文件末尾

>>> fd = open('../config/file1.txt','a',encoding='utf-8')
>>> fd.write('linux windows aix')
17
>>> fd.close()
>>> fd = open('../config/file1.txt','r',encoding='utf-8')
>>> fd.read()
'java rubby golinux windows aix'

5.'b'，二进制模式，比如流文件mp3，并且需要同时指定一种读写模式

>>> fd = open('/tmp/Front_Right.wav','b')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Must have exactly one of create/read/write/append mode and at most one plus
>>> fd = open('/tmp/Front_Right.wav','rb')
>>> fd1 = open('/tmp/Front_Right.wav','wb')
>>> fd2 = open('/tmp/Front_Right.wav','ab')
>>> fd2 = open('/tmp/Front_Right.wav','w+b')
>>> fd2 = open('/tmp/Front_Right.wav','r+b')

6.'t'，文本模式，默认打开文本并读取模式rt

7.'+'，打开硬盘文件读写

• r+，打开并写入

• >>> fd = open('../config/file1.txt','r+',encoding='utf-8')
  >>> fd.read()
  'java rubby golinux windows aix'
  >>> fd.write("mage")
  4
  >>> fd.seek(0)
  0
  >>> fd.read()
  'java rubby golinux windows aixmage'

• w+，打开文件读写，文件存在则覆盖，不存在则创建

• >>> fd = open('../config/file4.txt','w+',encoding='utf-8')
  >>> fd.write('guangzhou')
  9
  >>> fd.seek(0)
  0
  >>> fd.read()
  'guangzhou'
  >>> fd.seek(0)
  0
  >>> fd.write('hangzhou')
  8
  >>> fd.seek(0)
  0
  >>> fd.read()
  'hangzhouu'

• a+，打开文件读写，存在则将指针置于末尾，不存在则创建新文件

• >>> fd = open('../config/file4.txt','a+',encoding='utf-8')
  >>> fd.read()
  ''
  >>> fd.seek(0)
  0
  >>> fd.read()
  'hangzhouu'
  >>> fd.close()
  >>> fd = open('../config/file4.txt','a+',encoding='utf-8')
  >>> fd.write('beijing')
  7
  >>> fd.read()
  ''
  >>> fd.seek(0)
  0
  >>> fd.read()
  'hangzhouubeijing'

• rb+, wb+, ab+ 对象是二进制，其他以上面一样

8.‘U’，deprecated

指针位置

1.f.tell()，告知字符指针位置

2.f.seek()，移动字符指针位置，f.seek(0)文件开头

>>> fd = open('../config/file4.txt','r',encoding='utf-8')
>>> fd.tell()
0
>>> fd.seek(0)
0
>>> fd.tell()
0
>>> fd.read(1)
'h'
>>> fd.tell()
1
>>> fd.read(2)
'an'
>>> fd.tell()
3
>>> fd.seek(0)
0
>>> fd.readline()
'hangzhouubeijing
'
>>> fd.tell()
17

读取文件的4个read，默认从头开始读，并将将指针留在行尾

1.fd.read(size)

• 默认省略size，size为整型，字符个数
• 读取全部内容到内存，并将指针留在行尾
• 大文件读取不要用，占内存
• 返回的是字符串类型

• >>> fd = open('../config/file4.txt','r',encoding='utf-8')
  >>> fd.read()
  'hangzhouubeijing'
  >>> fd.seek(0)
  0
  >>> fd.read(1)
  'h'
  >>> fd.read(2)
  'an'
  >>> fd.read(3)
  'gzh'
  >>> fd.seek(0)
  0
  >>> fd.read(6)
  'hangzh'

2.fd.readline(size)

• 默认一行行读取，size与上面一样
• 占用内存小
• 每行结尾带换行符

• >>> fd = open('../config/file4.txt','r',encoding='utf-8')
  >>> fd.readline()
  'hangzhouubeijing
  '
  >>> fd.readline()
  'shenzhen
  '
  >>> fd.readline()
  'shanghai
  '
  >>> fd.readline(1)
  'a'
  >>> fd.readline(2)
  'nh'
  >>> fd.readline()
  'ui
  '
  >>> fd.readline()
  'guangdong
  '
  >>> fd.readline()
  'zhejiang'
  >>> fd.readline()
  ''

3.fd.readlines(size)

• 讲文本全部转换成列表，size表示下标

• >>> fd = open('../config/file4.txt','r',encoding='utf-8')
  >>> fd.readlines()
  ['hangzhouubeijing
  ', 'shenzhen
  ', 'shanghai
  ', 'anhui
  ', 'guangdong
  ', 'zhejiang']
  >>> fd.seek(0)
  0
  >>> fd.readlines(1)
  ['hangzhouubeijing
  ']
  >>> fd.readlines()
  ['shenzhen
  ', 'shanghai
  ', 'anhui
  ', 'guangdong
  ', 'zhejiang']

4.fd.readable()

• 返回布尔值，判断文件是否可读

• >>> fd = open('../config/file4.txt','r',encoding='utf-8')
  >>> fd.readable()
  True

循环遍历迭代文本内容对象（遍历操作都可以这么干）

>>> fd = open('../config/file4.txt','r',encoding='utf-8')
>>> for line in fd:
...     print(line)
... 
hangzhouubeijing

shenzhen

shanghai

anhui

guangdong

zhejiang
>>> fd.seek(0)
0
>>> for index,line in enumerate(fd.readlines()):
...     print(index,line)
... 
0 hangzhouubeijing

1 shenzhen

2 shanghai

3 anhui

4 guangdong

5 zhejiang
>>> 

其他方法

close(self, /) 关闭打开的文件

•  |      Flush and close the IO object.
•  |      
•  |      This method has no effect if the file is already closed.

detach(self, /) 干嘛用？

•  |      Separate the underlying buffer from the TextIOBase and return it.
•  |      After the underlying buffer has been detached, the TextIO is in an
•  |      unusable state.

>>> fd.detach()
<_io.BufferedReader name='../config/file4.txt'>
>>> fd.read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: underlying buffer has been detached

fileno(self, /) 返回文件描述符，干嘛用？

•  |      Returns underlying file descriptor if one exists.
•  |      OSError is raised if the IO object does not use a file descriptor.

>>> fd = open('../config/file4.txt','r',encoding='utf-8')
>>> fd.fileno()
4
>>> fd = open('../config/filexxx.txt','w+',encoding='utf-8')
>>> fd.fileno()
3

flush(self, /) 将缓存立即写入硬盘，提高效率

•  |      Flush write buffers, if applicable.
•  |      This is not implemented for read-only and non-blocking streams.

import time
import sys
for i in range(40):
    sys.stdout.write("#")
    sys.stdout.flush()
    time.sleep(0.1)

isatty(self, /) 是否连接到终端设备

•  |      Return whether this is an 'interactive' stream.
•  |      Return False if it can't be determined.

seekable(self, /)

•  |      Return whether object supports random access.
•  |      If False, seek(), tell() and truncate() will raise OSError.
•  |      This method may need to do a test seek().

truncate(self, pos=None, /)

•  |      Truncate file to size bytes.
•  |      File pointer is left unchanged.  Size defaults to the current IO
•  |      position as reported by tell().  Returns the new size.

>>> fd = open('../config/file4.txt','r+',encoding='utf-8')
>>> fd.truncate()
0

writable(self, /) 判断文件是否以写模式打开
 |      Return whether object was opened for writing.

>>> fd = open('../config/file4.txt','r+',encoding='utf-8')
>>> fd.writable()
True
>>> fd = open('../config/file1.txt','r',encoding='utf-8')
>>> fd.writable()
False

修改文件的两种方式：

1.全部读入内存，修改完毕之后覆盖写入源文件

2.一行一行读取内存，修改完毕之后写入新文件，用新文件覆盖旧文件