update docstrings

src/sourmash/index.py

@@ -28,6 +28,9 @@
 class MultiIndex - in-memory storage and selection of signatures from multiple
 index objects, using manifests.
 
+class DirectoryIndex - on-disk storage and selection of signatures from
+under a directory, requiring a manifest.
+
 class LazyLoadedIndex - lazy-loading wrapper for on-disk indices, using
 manifests. Signatures are kept on disk until requested; only manifests are
 retained, and no open file handles or signatures.
@@ -386,6 +389,8 @@ class LinearIndex(Index):
     """An Index for a collection of signatures. Can load from a .sig file.
 
     Note: does not use manifests. See MultiIndex for that functionality.
+
+    Concrete class; signatures held in memory; does not use manifests.
     """
     def __init__(self, _signatures=None, filename=None):
         self._signatures = []
@@ -437,6 +442,8 @@ def select(self, **kwargs):
 class LazyLinearIndex(Index):
     """An Index for lazy linear search of another database.
 
+    Wrapper class; does not use manifests.
+
     One of the main purposes of this class is to _force_ linear 'find'
     on index objects. So if this class wraps an SBT, for example, the
     SBT find method will be overriden with the linear 'find' from the
@@ -510,6 +517,8 @@ class ZipFileLinearIndex(Index):
     A read-only collection of signatures in a zip file.
 
     Does not support `insert` or `save`.
+
+    Concrete class; signatures dynamically loaded from disk; uses manifests.
     """
     is_database = True
 
@@ -833,6 +842,8 @@ class MultiIndex(Index):
 
     Note: this is an in-memory collection, and does not do lazy loading:
     all signatures are loaded upon instantiation and kept in memory.
+
+    Concrete class; signatures held in memory; builds and uses manifests.
     """
     def __init__(self, manifest, parent=None):
         self.manifest = manifest
@@ -991,7 +1002,10 @@ def select(self, **kwargs):
 
 
 class DirectoryIndex(Index):
-    """
+    """An Index for a collection of signature files under a directory.
+
+    Concrete class; signatures dynamically loaded from disk; uses manifests.
+
     Notes:
     * manifests for directories are _generated_ by MultiIndex :grin: :shrug:
     * Lazy - loads signatures only when requested
@@ -1012,7 +1026,7 @@ def __init__(self, parent, manifest):
     def load(cls, pathname):
         "Create a DirectoryIndex from a directory with an existing manifest."
         if not os.path.isdir(pathname):
-            raise ValueError(f"'{pathname}' must be a directory.")
+            raise ValueError(f"'{pathname}' must be a directory")
 
         manifest_path = os.path.join(pathname, "SOURMASH-MANIFEST.csv")
         if not os.path.exists(manifest_path):
@@ -1061,6 +1075,8 @@ class LazyLoadedIndex(Index):
     from disk every time they are needed (e.g. 'find(...)', 'signatures()').
 
     Can be used with LazyMultiIndex to support many such indices at once.
+
+    Wrapper class; signatures dynamically loaded from disk; uses manifests.
     """
     def __init__(self, filename, manifest):
         "Create an Index with given filename and manifest."
@@ -1139,6 +1155,8 @@ class LazyMultiIndex(Index):
     Differs from MultiIndex in that only the manifests are held in memory,
     not any of the signatures.
 
+    Wrapper class; signatures loaded index objects; uses manifests.
+
     CTB: could we get the same functionality from MultiIndex + LazyLoadedIndex?
     """
     def __init__(self, index_list, manifest_list):