filelike 0.3.0

filelike: a python module for creating and handling file-like objects.

This module takes care of the groundwork for implementing and manipulating objects that provide a rich file-like interface, including reading, writing, seeking and iteration. It also provides a number of useful classes built on top of this functionality.

The main class is FileLikeBase, which implements the entire file-like interface on top of primitive _read(), _write(), _seek() and _tell() methods. Subclasses may implement any or all of these methods to obtain the related higher-level file behaviors.

It also provides some nifty file-handling functions:

• open: mirrors the standard open() function but is much cleverer;

  URLs are automatically fetched, .bz2 files are transparently decompressed, and so-on.

• join: concatenate multiple file-like objects together so that they

  act like a single file.

• slice: access a section of a file-like object as if it were an

  independent file.

The “wrappers” subpackage contains a collection of useful classes built on top of this framework. These include:

• Translate: pass file contents through an arbitrary translation

  function (e.g. compression, encryption, …)

• Decrypt: on-the-fly reading and writing to an encrypted file

  (using PEP272 cipher API)

• UnBZip2: on-the-fly decompression of bzip’d files

  (like the standard library’s bz2 module, but accepts any file-like object)

As an example of the type of thing this module is designed to achieve, here’s how the Decrypt wrapper can be used to transparently access an encrypted file:

# Create the decryption key from Crypto.Cipher import DES cipher = DES.new(‘abcdefgh’,DES.MODE_ECB) # Open the encrypted file from filelike.wrappers import Decrypt f = Decrypt(file(“some_encrypted_file.bin”,”r”),cipher)

The object in ‘f’ now behaves as a file-like object, transparently decrypting the file on-the-fly as it is read.

The “pipeline” subpackage contains facilities for composing these wrappers in the form of a unix pipeline. In the following example, ‘f’ will read the first five lines of an encrypted file:

from filelike.pipeline import Decrypt, Head f = file(“some_encrypted_file.bin”) > Decrypt(cipher) | Head(lines=5)

Finally, two utility functions are provided for when code expects to deal with file-like objects:

• is_filelike(obj): checks that an object is file-like

• to_filelike(obj): wraps a variety of objects in a file-like interface