X-Git-Url: https://wannabe.guru.org/gitweb/?a=blobdiff_plain;f=directory_filter.py;h=5d3585e5686603a9e6112a4def4fbd256597c3f1;hb=e46158e49121b8a955bb07b73f5bcf9928b79c90;hp=9fa13c2c1169c9895af5de7c4494627cd972d735;hpb=64a9a97fdff29f4bb9eef4e80faaeaa520d59506;p=python_utils.git

diff --git a/directory_filter.py b/directory_filter.py
index 9fa13c2..5d3585e 100644
--- a/directory_filter.py
+++ b/directory_filter.py
@@ -1,29 +1,65 @@
 #!/usr/bin/env python3
 
+# © Copyright 2021-2022, Scott Gasch
+
+"""Two predicates that can help avoid unnecessary disk I/O by
+detecting if a particular file is identical to the contents about to
+be written or if a particular directory already contains a file that
+is identical to the one about to be written.  See examples below.
+"""
+
 import hashlib
+import logging
 import os
-from typing import Any, Optional
+from typing import Any, Dict, Optional, Set
+
+logger = logging.getLogger(__name__)
+
+
+class DirectoryFileFilter(object):
+    """A predicate that will return False if / when a proposed file's
+    content to-be-written is identical to the contents of the file on
+    disk allowing calling code to safely skip the write.
+
+    >>> testfile = '/tmp/directory_filter_text_f39e5b58-c260-40da-9448-ad1c3b2a69c2.txt'
+    >>> contents = b'This is a test'
+    >>> with open(testfile, 'wb') as wf:
+    ...     wf.write(contents)
+    14
+
+    >>> d = DirectoryFileFilter('/tmp')
 
-import predicate
-import file_utils
+    >>> d.apply(contents, testfile)     # False if testfile already contains contents
+    False
 
+    >>> d.apply(b'That was a test', testfile)    # True otherwise
+    True
+
+    >>> os.remove(testfile)
 
-class DirectoryFileFilter(predicate.Predicate):
-    """A predicate that will return False if when a proposed file's
-    content to-be-written is identical to the contents of the file;
-    skip the write.
     """
 
     def __init__(self, directory: str):
+        """C'tor.
+
+        Args:
+            directory: the directory we're filtering accesses to
+        """
         super().__init__()
+        import file_utils
+
         if not file_utils.does_directory_exist(directory):
             raise ValueError(directory)
         self.directory = directory
-        self.md5_by_filename = {}
-        self.mtime_by_filename = {}
+        self.md5_by_filename: Dict[str, str] = {}
+        self.mtime_by_filename: Dict[str, float] = {}
         self._update()
 
     def _update(self):
+        """
+        Internal method.  Foreach file in the directory, compute its
+        MD5 checksum via :meth:`_update_file`.
+        """
         for direntry in os.scandir(self.directory):
             if direntry.is_file(follow_symlinks=True):
                 mtime = direntry.stat(follow_symlinks=True).st_mtime
@@ -31,48 +67,128 @@ class DirectoryFileFilter(predicate.Predicate):
                 self._update_file(path, mtime)
 
     def _update_file(self, filename: str, mtime: Optional[float] = None):
+        """
+        Internal method.  Given a file and mtime, compute its MD5 checksum
+        and persist it in an internal map.
+        """
+        import file_utils
+
         assert file_utils.does_file_exist(filename)
         if mtime is None:
             mtime = file_utils.get_file_raw_mtime(filename)
+        assert mtime is not None
         if self.mtime_by_filename.get(filename, 0) != mtime:
             md5 = file_utils.get_file_md5(filename)
+            logger.debug('Computed/stored %s\'s MD5 at ts=%.2f (%s)', filename, mtime, md5)
             self.mtime_by_filename[filename] = mtime
             self.md5_by_filename[filename] = md5
 
-    def apply(self, item: Any, filename: str) -> bool:
+    def apply(self, proposed_contents: Any, filename: str) -> bool:
+        """Call this with the proposed new contents of filename in
+        memory and we'll compute the checksum of those contents and
+        return a value that indicates whether they are identical to
+        the disk contents already (so you can skip the write safely).
+
+        Args:
+            proposed_contents: the contents about to be written to
+                filename
+            filename: the file about to be populated with
+                proposed_contents
+
+        Returns:
+            True if the disk contents of the file are identical to
+            proposed_contents already and False otherwise.
+        """
         self._update_file(filename)
         file_md5 = self.md5_by_filename.get(filename, 0)
+        logger.debug('%s\'s checksum is %s', filename, file_md5)
         mem_hash = hashlib.md5()
-        mem_hash.update(item)
+        mem_hash.update(proposed_contents)
         md5 = mem_hash.hexdigest()
+        logger.debug('Item\'s checksum is %s', md5)
         return md5 != file_md5
 
 
 class DirectoryAllFilesFilter(DirectoryFileFilter):
     """A predicate that will return False if a file to-be-written to a
     particular directory is identical to any other file in that same
-    directory.
+    directory (regardless of its name).
+
+    i.e. this is the same as :class:`DirectoryFileFilter` except that
+    our apply() method will return true not only if the contents to be
+    written are identical to the contents of filename on the disk but
+    also it returns true if there exists some other file sitting in
+    the same directory which already contains those identical
+    contents.
+
+    >>> testfile = '/tmp/directory_filter_text_f39e5b58-c260-40da-9448-ad1c3b2a69c3.txt'
+
+    >>> contents = b'This is a test'
+    >>> with open(testfile, 'wb') as wf:
+    ...     wf.write(contents)
+    14
+
+    >>> d = DirectoryAllFilesFilter('/tmp')
+
+    >>> d.apply(contents)    # False is _any_ file in /tmp contains contents
+    False
+
+    >>> d.apply(b'That was a test')    # True otherwise
+    True
+
+    >>> os.remove(testfile)
+
     """
 
     def __init__(self, directory: str):
-        self.all_md5s = set()
+        """C'tor.
+
+        Args:
+            directory: the directory we're watching
+        """
+        self.all_md5s: Set[str] = set()
         super().__init__(directory)
-        print(self.all_md5s)
 
     def _update_file(self, filename: str, mtime: Optional[float] = None):
+        """Internal method.  Given a file and its mtime, update internal
+        state.
+        """
+        import file_utils
+
         assert file_utils.does_file_exist(filename)
         if mtime is None:
             mtime = file_utils.get_file_raw_mtime(filename)
+        assert mtime is not None
         if self.mtime_by_filename.get(filename, 0) != mtime:
             md5 = file_utils.get_file_md5(filename)
             self.mtime_by_filename[filename] = mtime
             self.md5_by_filename[filename] = md5
             self.all_md5s.add(md5)
 
-    def apply(self, item: Any) -> bool:
+    def apply(self, proposed_contents: Any, ignored_filename: str = None) -> bool:
+        """Call this before writing a new file to directory with the
+        proposed_contents to be written and it will return a value that
+        indicates whether the identical contents is already sitting in
+        *any* file in that directory.  Useful, e.g., for caching.
+
+        Args:
+            proposed_contents: the contents about to be persisted to
+                directory
+            ignored_filename: unused for now, must be None
+
+        Returns:
+            True if proposed contents does not yet exist in any file in
+            directory or False if it does exist in some file already.
+        """
+        assert ignored_filename is None
         self._update()
         mem_hash = hashlib.md5()
-        mem_hash.update(item)
+        mem_hash.update(proposed_contents)
         md5 = mem_hash.hexdigest()
         return md5 not in self.all_md5s
 
+
+if __name__ == '__main__':
+    import doctest
+
+    doctest.testmod()