Allow compound file extensions

os.path.splitext thinks that the extension for file.fits.gz
is .gz -- from a butler perspective it has to be .fits.gz
so change to use Path.suffixes in Location and ButlerURI.

python/lsst/daf/butler/core/formatter.py

@@ -325,7 +325,7 @@ def validateExtension(cls, location: Location) -> None:
 
         if ext in supported:
             return
-        raise ValueError(f"Extension '{ext}' is not supported by Formatter '{cls.__name__}'")
+        raise ValueError(f"Extension '{ext}' on '{location}' is not supported by Formatter '{cls.__name__}'")
 
     def predictPath(self) -> str:
         """Return the path that would be returned by write, without actually

python/lsst/daf/butler/core/location.py

@@ -292,19 +292,21 @@ def updateFile(self, newfile: str) -> None:
         self._uri = self._uri._replace(path=newpath)
 
     def getExtension(self) -> str:
-        """Return the file extension associated with this URI path.
+        """Return the file extension(s) associated with this URI path.
 
         Returns
         -------
         ext : `str`
             The file extension (including the ``.``). Can be empty string
-            if there is no file extension.
+            if there is no file extension. Will return all file extensions
+            as a single extension such that ``file.fits.gz`` will return
+            a value of ``.fits.gz``.
         """
         if not self.scheme:
-            _, ext = os.path.splitext(self.path)
+            extensions = PurePath(self.path).suffixes
         else:
-            _, ext = posixpath.splitext(self.path)
-        return ext
+            extensions = PurePosixPath(self.path).suffixes
+        return "".join(extensions)
 
     def __str__(self) -> str:
         return self.geturl()
@@ -547,6 +549,8 @@ def relativeToPathRoot(self) -> str:
     def updateExtension(self, ext: Optional[str]) -> None:
         """Update the file extension associated with this `Location`.
 
+        All file extensions are replaced.
+
         Parameters
         ----------
         ext : `str`
@@ -556,10 +560,12 @@ def updateExtension(self, ext: Optional[str]) -> None:
         if ext is None:
             return
 
-        if not self._datastoreRootUri.scheme:
-            path, _ = os.path.splitext(self.pathInStore)
-        else:
-            path, _ = posixpath.splitext(self.pathInStore)
+        # Get the extension and remove it from the path if one is found
+        # .fits.gz counts as one extension do not use os.path.splitext
+        current = self.getExtension()
+        path = self.pathInStore
+        if current:
+            path = path[:-len(current)]
 
         # Ensure that we have a leading "." on file extension (and we do not
         # try to modify the empty string)
@@ -569,19 +575,21 @@ def updateExtension(self, ext: Optional[str]) -> None:
         self._path = path + ext
 
     def getExtension(self) -> str:
-        """Return the file extension associated with this location.
+        """Return the file extension(s) associated with this location.
 
         Returns
         -------
         ext : `str`
             The file extension (including the ``.``). Can be empty string
-            if there is no file extension.
+            if there is no file extension. Will return all file extensions
+            as a single extension such that ``file.fits.gz`` will return
+            a value of ``.fits.gz``.
         """
         if not self._datastoreRootUri.scheme:
-            _, ext = os.path.splitext(self.pathInStore)
+            extensions = PurePath(self.path).suffixes
         else:
-            _, ext = posixpath.splitext(self.pathInStore)
-        return ext
+            extensions = PurePath(self.path).suffixes
+        return "".join(extensions)
 
 
 class LocationFactory:

tests/test_location.py

@@ -127,11 +127,15 @@ def testFileLocation(self):
         self.assertTrue(loc1.uri.startswith("file:///"))
         self.assertTrue(loc1.uri.endswith("file.ext"))
         loc1.updateExtension("fits")
-        self.assertTrue(loc1.uri.endswith("file.fits"))
+        self.assertTrue(loc1.uri.endswith("file.fits"), f"Checking 'fits' extension in {loc1.uri}")
+        loc1.updateExtension("fits.gz")
+        self.assertTrue(loc1.uri.endswith("file.fits.gz"), f"Checking 'fits.gz' extension in {loc1.uri}")
+        loc1.updateExtension(".jpeg")
+        self.assertTrue(loc1.uri.endswith("file.jpeg"), f"Checking 'jpeg' extension in {loc1.uri}")
         loc1.updateExtension(None)
-        self.assertTrue(loc1.uri.endswith("file.fits"))
+        self.assertTrue(loc1.uri.endswith("file.jpeg"), f"Checking unchanged extension in {loc1.uri}")
         loc1.updateExtension("")
-        self.assertTrue(loc1.uri.endswith("file"))
+        self.assertTrue(loc1.uri.endswith("file"), f"Checking no extension in {loc1.uri}")
 
     def testRelativeRoot(self):
         root = os.path.abspath(os.path.curdir)