filelike 0.2.2

Classes for creating and wrapping file-like objects

The filelike module takes care of the groundwork for implementing and handling file-like objects that implement a rich file-like interface, including reading, writing, 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 (currently minus seek() and tell()) on top of primitive _read() and _write() methods. Subclasses may implement either or both of these methods to obtain all the higher-level file behaviors.

Two methods 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

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

• TransFile: pass file contents through an arbitrary translation

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

• FixedBlockSizeFile: ensure all read/write requests are aligned with

  a given blocksize

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

  (using PEP272 cipher API)

As an example of the type of thing this module is designed to achieve, here’s an example of using the DecryptFile class 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 DecryptFile f = DecryptFile(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 this example, <f> will read the first five lines of an encrypted file:

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

Finally, the function filelike.open() mirrors the standard file opening function but tries to be clever about accessing the file - URLs are automatically fetched using urllib2, compressed files are decompressed on-the-fly, and so-forth.