python 5-4 如何將文件映射到內存
解決方案
使用標準庫中mmap模塊的mmap函數,它需要一個打開文件描述符作爲參數
Unix: mmap(fileno, length[, flags[, prot[, access[, offset]]]])
#文件描述符獲取方法
1.os.open()
2.f=open("test.txt",20) f.fileno ==>獲得文件描述符
使用dd 創建大小爲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