Since this thing is on the innerwebs I suppose it should have a

[python_utils.git] / directory_filter.py

diff --git a/directory_filter.py b/directory_filter.py
index d275cf24d4e23a6be64fe4073ca4b3860c83ea3c..69e5547255e20ac66cfea81658867c8697501126 100644 (file)
--- a/directory_filter.py
+++ b/directory_filter.py
@@ -1,24 +1,55 @@
 #!/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 to be written.  See class docs below for
+examples.
+
+"""
+
 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;
-    skip the write.
+    """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')
+
+    >>> 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)
+
     """
 
     def __init__(self, directory: str):
-        import file_utils
         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):
@@ -30,20 +61,25 @@ class DirectoryFileFilter(object):
 
     def _update_file(self, filename: str, mtime: Optional[float] = None):
         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:
         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)
         md5 = mem_hash.hexdigest()
+        logger.debug('Item\'s checksum is %s', md5)
         return md5 != file_md5
 
 
@@ -51,27 +87,58 @@ 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.
+
+    i.e. this is the same as the above except that its 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()
+        self.all_md5s: Set[str] = set()
         super().__init__(directory)
-        print(self.all_md5s)
 
     def _update_file(self, filename: str, mtime: Optional[float] = None):
         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, item: Any, ignored_filename: str = None) -> bool:
+        assert ignored_filename is None
         self._update()
         mem_hash = hashlib.md5()
         mem_hash.update(item)
         md5 = mem_hash.hexdigest()
         return md5 not in self.all_md5s
+
+
+if __name__ == '__main__':
+    import doctest
+
+    doctest.testmod()