file_metadata: Add class GenericFile

The GenericFile is the basic scaffolding for all files that can
be analyzed. It is a base class for other formats and also holds
analysis methods which are applicable to all files.

Fixes #5

file_metadata/generic_file.py

@@ -0,0 +1,57 @@
+# -*- coding: utf-8 -*-
+
+from __future__ import (division, absolute_import, unicode_literals,
+                        print_function)
+
+from file_metadata.utilities import PropertyCached
+
+
+class GenericFile:
+    """
+    Object corresponding to a single file. An abstract class that can be
+    used for any mimetype/media-type (depending of the file itself). Provides
+    helper functions to open files, and analyze basic data common to all
+    types of files.
+
+    Any class that inherits from this abstract class would probably want to
+    set the ``mimetypes`` and override the ``analyze()`` or write their
+    own ``analyze_*()`` methods depending on the file type and analysis
+    routines that should be run.
+
+    :ivar mimetypes: Set of mimetypes (strings) applicable to this class
+        based on the official standard by IANA.
+    """
+    mimetypes = ()
+
+    def __init__(self, fname):
+        self.filename = fname
+
+    def analyze(self, prefix='analyze_', suffix='', methods=None):
+        """
+        Analyze the given file and create metadata information appropriately.
+        Search and use all methods that have a name starting with
+        ``analyze_*`` and merge the doctionaries using ``.update()``
+        to get the cumulative set of metadata.
+
+        :param prefix:  Use only methods that have this prefix.
+        :param suffix:  Use only methods that have this suffix.
+        :param methods: A list of method names to choose from. If not given,
+                        a sorted list of all methods from the class is used.
+        :return: A dict containing the cumulative metadata.
+        """
+        data = {}
+        methods = methods or sorted(dir(self))
+        for method in methods:
+            if method.startswith(prefix) and method.endswith(suffix):
+                data.update(getattr(self, method)())
+        return data
+
+    @PropertyCached
+    def metadata(self):
+        """
+        A python dictionary of all the metadata identified by analyzing
+        the given file. This property is read-only and cannot be modified.
+
+        :return: All the metadata found about the given file.
+        """
+        return self.analyze()

tests/generic_file_test.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+
+from __future__ import (division, absolute_import, unicode_literals,
+                        print_function)
+
+from file_metadata.generic_file import GenericFile
+from tests import fetch_file, unittest
+
+
+class DerivedFile(GenericFile):
+
+    def analyze(self):
+        # Only use the `_analyze_test` functions for tests
+        return GenericFile.analyze(self, prefix='analyze_test')
+
+    def analyze_test1(self):
+        return {"test1": "test1"}
+
+    def analyze_test2(self):
+        return {"test2": "test2"}
+
+
+class DerivedFileTest(unittest.TestCase):
+
+    def setUp(self):
+        self.uut = DerivedFile(fetch_file('ascii.txt'))
+
+    def test_metadata(self):
+        self.assertEqual(self.uut.metadata, {'test1': 'test1',
+                                             'test2': 'test2'})