python 文件流

open | write | read

>>> with open('demo.txt' , 'wt') as f:   #以文本(wt)形式写入操作

...     f.write("hello guohai")

12

>>> with open('demo.txt' , 'rt') as f: #以文本(rt)形式读取操作

...     data = f.read()

>>> data

'hello guohai'

>>> with open('demo.txt' , 'at') as f: #以文本(at)形式追加操作

...     f.write('hello zeopean')

13

>>> with open('demo.txt' , 'rt') as f:

...     data = f.read()

>>> data

'hello guohaihello zeopean'

 

 

 

-- print 输出到文件中

with open('d:/work/test.txt', 'wt') as f:

print('Hello World!', file=f)

　　

-- 二进制读写

如果你想从二进制模式的文件中读取或写入文本数据，必须确保要进行解码和编码

操作。比如：

with open('somefile.bin', 'rb') as f:

data = f.read(16)

text = data.decode('utf-8')

with open('somefile.bin', 'wb') as f:

text = 'Hello World'

f.write(text.encode('utf-8'))

 

-- 判断文件是否存在

>>> import os

>>> if not os.path.exists('somefile'):

... with open('somefile', 'wt') as f:

... f.write('Hello
')

... else:

... print('File already exists!')

...

File already exists!

StringIO | BytesIO

-- StringIO

>>> s = io.StringIO()

>>> s.write('Hello World
')

12

>>> print('This is a test', file=s)

15

>>> s.getvalue()

'Hello World
This is a test
'

>>>

>>> s = io.StringIO('Hello
World
')

>>> s.read(4)

'Hell'

>>> s.read()

'o
World
'

>>>

 

-- BytesIO

>>> s = io.BytesIO()

>>> s.write(b'binary data')

>>> s.getvalue()

b'binary data'

>>>

readinto | bytearray | memoryview

record_size = 32  

buf = bytearray(record_size)

with open('somefile', 'rb') as f:

while True:

n = f.readinto(buf)

if n < record_size:

break

 

另外有一个有趣特性就是 memoryview ，它可以通过零复制的方式对已存在的缓冲

区执行切片操作，甚至还能修改它的内容。比如：

>>> buf

bytearray(b'Hello World')

>>> m1 = memoryview(buf)

>>> m2 = m1[-5:]

>>> m2

<memory at 0x100681390>

>>> m2[:] = b'WORLD'

>>> buf

bytearray(b'Hello WORLD')

mmap 

-- 内存映射的二进制文件

import os

import mmap

 

def memory_map(filename , access=mmap.ACCESS_WRITE):

size = os.path.getsize(filename)

fd = os.open(filename , os.O_RDWR)

return mmap.mmap(fd ,size , access=access)

 

size = 1000000

with open('data' , 'wb') as f:

f.seek(size - 1)

f.write(b'x00')

 

m = memory_map('data')

print(len(m))

 

print(m[0:10])

 

# print(b'hello daming' , file=m[0:11])

# m.close()

 

with open('data' ,'rb') as f:

print(f.read(11))

os.path

-- basename | dirname | join | splitext | expanduser

import os

>>> path = 'demo.bin'

>>> os.path.basename(path) #文件名

'demo.bin'

>>> os.path.dirname(path) #文件路径

''

>>> os.path.join('tmp','data' , os.path.basename(path))  #路径拼接

'tmp\data\demo.bin'

>>> path = '~/data/data.bin'

>>> os.path.expanduser(path) #系统路径

'C:\Users\Administrator/data/data.bin'

>>> os.path.splitext(path) #获取后缀名

('~/data/data', '.bin')

-- exists | isdir | islink | realpath

os.path.exists('/etc/passwd')   #判断文件是否存在

>>> os.path.isdir('user.data')  #判断是否是目录

False

>>> os.path.islink('demo.bin')  #判断是否是超链接

False

>>> os.path.realpath('demo.bin') #获取文件的绝对路径

'E:\zeopean\pycode\pyfunc\demo.bin'

-- getmtime | getsize 获取元数据

>>> os.path.getmtime('demo.txt')

1459387735.7783203

>>> import time

>>> time.ctime(os.path.getmtime('demo.bin'))

'Thu Mar 31 10:27:36 2016'

>>> os.path.getsize('demo.txt')

47

-- listdir 

>>> names = os.listdir('.')

>>> names

['closure.func.py', 'closureInstance.py', 'data', 'demo.bin', 'demo.txt', 'file.

txt', 'make_element.py', 'mmap.demo.py', 'readinto.demo.py', 'yield.func.py']

tempfile

--临时文件 TemporaryFile

from tempfile import TemporaryFile

f = TemporaryFile('w+t')

# Use the temporary file

...

f.close()

 

--有名字的临时文件 NamedTemporaryFile

from tempfile import NamedTemporaryFile

with NamedTemporaryFile('w+t') as f:

print('filename is:', f.name)

 

-- 临时目录 TemporaryDirectory

from tempfile import TemporaryDirectory

with TemporaryDirectory() as dirname:

print('dirname is:', dirname) 

 

-- 插件临时文件 mkstemp | mkdtemp

>>> import tempfile

>>> tempfile.mkstemp()

(3, 'C:\Users\ADMINI~1\AppData\Local\Temp\tmp_jbpp74i')

>>> tempfile.mkdtemp()

'C:\Users\ADMINI~1\AppData\Local\Temp\tmpkwsqedpa'

 

-- 获取临时文件名  gettempdir

import tempfile

tempfile.gettempdir()

'C:\Users\ADMINI~1\AppData\Local\Temp'

Pickle

-- 序列化对象

>>> import pickle

>>> f = open('somedata', 'wb')

>>> pickle.dump([1, 2, 3, 4], f)

>>> pickle.dump('hello', f)

>>> pickle.dump({'Apple', 'Pear', 'Banana'}, f)

>>> f.close()

>>> f = open('somedata', 'rb')

>>> pickle.load(f)

[1, 2, 3, 4]

>>> pickle.load(f)

'hello'

>>> pickle.load(f)

{'Apple', 'Pear', 'Banana'}