Add matplotlib.figure.Figure storage to PosixStorage.

Matplotlib figures cannot be retrieved using the butler,
but 'put' should now work.

Note that this storage actually only requires that the object
being saved have a `savefig` method with the same behavior
as matplotlib's.

python/lsst/daf/persistence/posixStorage.py

@@ -293,7 +293,7 @@ def butlerLocationExists(self, location):
         storageName = location.getStorageName()
         if storageName not in ('BoostStorage', 'FitsStorage', 'PafStorage',
                                'PickleStorage', 'ConfigStorage', 'FitsCatalogStorage',
-                               'ParquetStorage'):
+                               'ParquetStorage', 'MatplotlibStorage'):
             self.log.warn("butlerLocationExists for non-supported storage %s" % location)
             return False
         for locationString in location.getLocations():
@@ -780,6 +780,57 @@ def writeFitsCatalogStorage(butlerLocation, obj):
         return
 
 
+def readMatplotlibStorage(butlerLocation):
+    """Read from a butlerLocation (always fails for this storage type).
+
+    Parameters
+    ----------
+    butlerLocation : ButlerLocation
+        The location & formatting for the object(s) to be read.
+
+    Returns
+    -------
+    A list of objects as described by the butler location. One item for
+    each location in butlerLocation.getLocations()
+    """
+    raise NotImplementedError("Figures saved with MatplotlibStorage cannot be retreived using the Butler.")
+
+
+def writeMatplotlibStorage(butlerLocation, obj):
+    """Writes a matplotlib.figure.Figure to a location, using the template's
+    filename suffix to infer the file format.
+
+    Parameters
+    ----------
+    butlerLocation : ButlerLocation
+        The location & formatting for the object to be written.
+    obj : matplotlib.figure.Figure
+        The object to be written.
+
+    Raises
+    ------
+    ValueError
+        Raised if the file
+    """
+    additionalData = butlerLocation.getAdditionalData()
+    locations = butlerLocation.getLocations()
+    with SafeFilename(os.path.join(butlerLocation.getStorage().root, locations[0])) as locationString:
+        logLoc = LogicalLocation(locationString, additionalData)
+        # SafeFilename appends a random suffix, which corrupts the extension
+        # matplotlib uses to guess the file format.
+        # Instead, we strip off the extension from the original location
+        # and pass that as the format directly.
+        _, ext = os.path.splitext(locations[0])
+        if ext:
+            ext = ext[1:]  # strip off leading '.'
+        else:
+            # If there is no extension, we let matplotlib fall back to its
+            # default.
+            ext = None
+        obj.savefig(logLoc.locString(), format=ext)
+        return
+
+
 def readPafStorage(butlerLocation):
     """Read from a butlerLocation.
 
@@ -861,6 +912,7 @@ def writeBoostStorage(butlerLocation, obj):
 PosixStorage.registerFormatters("ConfigStorage", readConfigStorage, writeConfigStorage)
 PosixStorage.registerFormatters("PickleStorage", readPickleStorage, writePickleStorage)
 PosixStorage.registerFormatters("FitsCatalogStorage", readFitsCatalogStorage, writeFitsCatalogStorage)
+PosixStorage.registerFormatters("MatplotlibStorage", readMatplotlibStorage, writeMatplotlibStorage)
 PosixStorage.registerFormatters("PafStorage", writeFormatter=readPafStorage)
 PosixStorage.registerFormatters("YamlStorage", readFormatter=readYamlStorage)
 PosixStorage.registerFormatters("BoostStorage", readFitsStorage, writeFitsStorage)