API: separation of fields and mappers

.commitlint.rules.js

@@ -11,6 +11,7 @@ module.exports = {
         "covariance",
         "io",
         "fields",
+        "maps",
         "plot",
         "progress",
         "twopoint",

heracles/catalog/base.py

@@ -126,6 +126,11 @@ def __getitem__(self, where):
         """create a view with the given selection"""
         ...
 
+    @property
+    def metadata(self):
+        """return a dictionary of metadata for the catalogue"""
+        ...
+
     @property
     def label(self):
         """return a human-friendly identifier for the source of data"""
@@ -200,6 +205,11 @@ def base(self):
         """base catalogue of this view"""
         return self._catalog
 
+    @property
+    def metadata(self):
+        """return metadata for this view"""
+        return self._catalog.metadata
+
     @property
     def label(self):
         """human-friendly label of the catalogue (not settable in view)"""
@@ -325,6 +335,15 @@ def base(self):
         """returns ``None`` since this is not a view of another catalogue"""
         return
 
+    @property
+    def metadata(self):
+        """return the metadata for this catalogue"""
+        return MappingProxyType(
+            {
+                "catalog": self._label,
+            },
+        )
+
     @property
     def label(self):
         """optional human-friendly label for catalogue"""

heracles/core.py

@@ -49,6 +49,23 @@ def toc_filter(obj, include=None, exclude=None):
     raise TypeError(msg)
 
 
+def toc_nearest(obj, key):
+    """return the closest match to *key* in *obj*."""
+    if isinstance(key, Sequence):
+        t = tuple(key)
+    else:
+        t = (key,)
+    while t:
+        if t in obj:
+            return obj[t]
+        if len(t) == 1 and t[0] in obj:
+            return obj[t[0]]
+        t = t[:-1]
+    if t in obj:
+        return obj[t]
+    raise KeyError(key)
+
+
 # subclassing UserDict here since that returns the correct type from methods
 # such as __copy__(), __or__(), etc.
 class TocDict(UserDict):
@@ -90,11 +107,13 @@ def __getitem__(self, pattern):
         return found
 
 
-def update_metadata(array, **metadata):
+def update_metadata(array, *sources, **metadata):
     """update metadata of an array dtype"""
     md = {}
     if array.dtype.metadata is not None:
         md.update(array.dtype.metadata)
+    for source in sources:
+        md.update(source.metadata)
     md.update(metadata)
     # create the new dtype with only the new metadata
     dt = array.dtype