The mmap Module

(New in 2.0) The mmap module provides an interface to the operating system's memory mapping functions, as shown in Example 2-13. The mapped region behaves like a string object, but data is read directly from the file.

Example 2-13. Using the mmap Module

File: mmap-example-1.py

import mmap
import os

filename = "samples/sample.txt"

file = open(filename, "r+")
size = os.path.getsize(filename)

data = mmap.mmap(file.fileno(), size)

# basics
print data
print len(data), size

# use slicing to read from the file
print repr(data[:10]), repr(data[:10])

# or use the standard file interface
print repr(data.read(10)), repr(data.read(10))


302 302
'We will pe' 'We will pe'
'We will pe' 'rhaps even'

Under Windows, the file must currently be opened for both reading and writing (r+, or w+), or the mmap call will fail.

Example 2-14 shows that memory mapped regions can be used instead of ordinary strings in many places, including regular expressions and many string operations.

Example 2-14. Using String Functions and Regular Expressions on a Mapped Region

File: mmap-example-2.py

import mmap
import os, string, re

def mapfile(filename):
 file = open(filename, "r+")
 size = os.path.getsize(filename)
 return mmap.mmap(file.fileno(), size)

data = mapfile("samples/sample.txt")

# search
index = data.find("small")
print index, repr(data[index-5:index+15])

# regular expressions work too!
m = re.search("small", data)
print m.start(), m.group()

43 'only small1512modules '
43 small