Python - mechanism to identify compressed file type and uncompress

Question

A compressed file can be classified into below logical groups
a. The operating system which you are working on (*ix, Win) etc.
b. Different types of compression algo

Answer 1

Based on lazyr's answer and my comment, here is what I mean:

class CompressedFile (object):
    magic = None
    file_type = None
    mime_type = None
    proper_extension = None

    def __init__(self, f):
        # f is an open file or file like object
        self.f = f
        self.accessor = self.open()

    @classmethod
    def is_magic(self, data):
        return data.startswith(self.magic)

    def open(self):
        return None

import zipfile

class ZIPFile (CompressedFile):
    magic = '\x50\x4b\x03\x04'
    file_type = 'zip'
    mime_type = 'compressed/zip'

    def open(self):
        return zipfile.ZipFile(self.f)

import bz2

class BZ2File (CompressedFile):
    magic = '\x42\x5a\x68'
    file_type = 'bz2'
    mime_type = 'compressed/bz2'

    def open(self):
        return bz2.BZ2File(self.f)

import gzip

class GZFile (CompressedFile):
    magic = '\x1f\x8b\x08'
    file_type = 'gz'
    mime_type = 'compressed/gz'

    def open(self):
        return gzip.GzipFile(self.f)


# factory function to create a suitable instance for accessing files
def get_compressed_file(filename):
    with file(filename, 'rb') as f:
        start_of_file = f.read(1024)
        f.seek(0)
        for cls in (ZIPFile, BZ2File, GZFile):
            if cls.is_magic(start_of_file):
                return cls(f)

        return None

filename='test.zip'
cf = get_compressed_file(filename)
if cf is not None:
    print filename, 'is a', cf.mime_type, 'file'
    print cf.accessor

Can now access the compressed data using cf.accessor. All the modules provide similar methods like 'read()', 'write()', etc. to do this.