python 5-4 如何将文件映射到内存mmap.mmap(f.fileno(),0,access=mmap.ACCESS_WRITE)

python 5-4 如何将文件映射到内存

解决方案

使用标准库中mmap模块的mmap函数,它需要一个打开文件描述符作为参数
Unix: mmap(fileno, length[, flags[, prot[, access[, offset]]]])

#文件描述符获取方法

 1.os.open()
 2.f=open("test.txt",20) f.fileno ==>获得文件描述符

使用dd 创建大小为1M的文件

dd if=/dev/zero of=test.bin bs=1024 count=1024
od -x test.bin 
0000000 0000 0000 0000 0000 0000 0000 0000 0000
*
4000000

import os 
import mmap
f=open("test.bin","r+b")
m=mmap.mmap(f.fileno(),0,access=mmap.ACCESS_WRITE)
m[0]='\x88'
m[4:8]='\xad'*4

m2=mmap.mmap(f.fileno(),mmap.PAGESIZE * 8,access=mmap.ACCESS_WRITE,offset=mmap.PAGESIZE * 4)
m2[:0x1000]='\xaa'* 0x1000



#########################################################

od -x test.bin
0000000 0088 0000 adad adad 0000 0000 0000 0000
0000020 0000 0000 0000 0000 0000 0000 0000 0000
*
0040000 aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa
*
0050000 0000 0000 0000 0000 0000 0000 0000 0000
*
4000000

help(mmap.mmap)

Help on class mmap in module mmap:

class mmap(__builtin__.object)
 |  Windows: mmap(fileno, length[, tagname[, access[, offset]]])
 |  
 |  Maps length bytes from the file specified by the file handle fileno,
 |  and returns a mmap object.  If length is larger than the current size
 |  of the file, the file is extended to contain length bytes.  If length
 |  is 0, the maximum length of the map is the current size of the file,
 |  except that if the file is empty Windows raises an exception (you cannot
 |  create an empty mapping on Windows).
 |  
 |  Unix: mmap(fileno, length[, flags[, prot[, access[, offset]]]])
 |  
 |  Maps length bytes from the file specified by the file descriptor fileno,
 |  and returns a mmap object.  If length is 0, the maximum length of the map
 |  will be the current size of the file when mmap is called.
 |  flags specifies the nature of the mapping. MAP_PRIVATE creates a
 |  private copy-on-write mapping, so changes to the contents of the mmap
 |  object will be private to this process, and MAP_SHARED creates a mapping
 |  that's shared with all other processes mapping the same areas of the file.
 |  The default value is MAP_SHARED.
 |  
 |  To map anonymous memory, pass -1 as the fileno (both versions).
 |  
 |  Methods defined here:
 |  
 |  __add__(...)
 |      x.__add__(y) <==> x+y
 |  
 |  __delitem__(...)
 |      x.__delitem__(y) <==> del x[y]
 |  
 |  __delslice__(...)
 |      x.__delslice__(i, j) <==> del x[i:j]
 |      
 |      Use of negative indices is not supported.
 |  
 |  __getattribute__(...)
 |      x.__getattribute__('name') <==> x.name
 |  
 |  __getitem__(...)
 |      x.__getitem__(y) <==> x[y]
 |  
 |  __getslice__(...)
 |      x.__getslice__(i, j) <==> x[i:j]
 |      
 |      Use of negative indices is not supported.
 |  
 |  __len__(...)
 |      x.__len__() <==> len(x)
 |  
 |  __mul__(...)
 |      x.__mul__(n) <==> x*n
 |  
 |  __rmul__(...)
 |      x.__rmul__(n) <==> n*x
 |  
 |  __setitem__(...)
 |      x.__setitem__(i, y) <==> x[i]=y
 |  
 |  __setslice__(...)
 |      x.__setslice__(i, j, y) <==> x[i:j]=y
 |      
 |      Use  of negative indices is not supported.
 |  
 |  close(...)
 |  
 |  find(...)
 |  
 |  flush(...)
 |  
 |  move(...)
 |  
 |  read(...)
 |  
 |  read_byte(...)
 |  
 |  readline(...)
 |  
 |  resize(...)
 |  
 |  rfind(...)
 |  
 |  seek(...)
 |  
 |  size(...)
 |  
 |  tell(...)
 |  
 |  write(...)
 |  
 |  write_byte(...)
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  __new__ = <built-in method __new__ of type object>
 |      T.__new__(S, ...) -> a new object with type S, a subtype of T