Python内存映射文件读写方式

import os
import time
import mmap
 
filename = 'test.txt'
 
#如果不存在，创建。
if not os.path.exists(filename):
 open(filename, 'w')
 
print(os.path.isdir(filename))
if os.path.isfile(filename):
 print(time.ctime(os.path.getctime(filename)))
 
fd = os.open(filename, os.O_RDWR)
m = mmap.mmap(fd, 50, access=mmap.ACCESS_WRITE) # 1024字节的文件。
m.seek(2) 
buf1 = bytes(b'Zhang')
m[2:len(buf1)+2] = buf1
 
buf2 = b'Phil'
 
m.seek(20) # 定位写入的位置。
m.write(buf2) # 写入字节数据。
m.close()
 
fd = os.open(filename, os.O_RDWR)
m = mmap.mmap(fd, 50, access=mmap.ACCESS_READ)
m.seek(20)
buf3 = m.read(len(buf2))
m.close()
print(list(buf3))

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')
>>> len(m)
1000000
>>> m[:10]
b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
>>> m[0]
0
>>> m[0:11]=b'Hello World'#改变一个切片
>>> m.close()
>>> with open('data','rb') as f:#验证改变已经生效
 print(f.read(11))
 
b'Hello World'

>>> with memory_map('data') as m:
 print(len(m))
 print(m[0:11])
 
1000000
b'Hello World'