DM-15871: add smart doImport function from daf_butler

python/lsst/utils/__init__.py

@@ -29,6 +29,7 @@
 from .demangle import *
 from .utils import *
 from .get_caller_name import *
+from .doImport import *
 from .wrappers import *
 from .python import *
 from .version import *

python/lsst/utils/doImport.py

@@ -0,0 +1,88 @@
+# This file is part of utils.
+#
+# Developed for the LSST Data Management System.
+# This product includes software developed by the LSST Project
+# (http://www.lsst.org).
+# See the COPYRIGHT file at the top-level directory of this distribution
+# for details of code ownership.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+import importlib
+
+__all__ = ("doImport",)
+
+
+def doImport(importable):
+    """Import a python object given an importable string and return it.
+
+    Parameters
+    ----------
+    importable : `str`
+        String containing dot-separated path of a Python class, module,
+        or member function.
+
+    Returns
+    -------
+    type : `type`
+        Type object. Either a module or class or a function.
+
+    Raises
+    ------
+    TypeError
+        ``importable`` is not a `str`.
+    ModuleNotFoundError
+        No module in the supplied import string could be found.
+    ImportError
+        ``importable`` is found but can not be imported or the requested
+        item could not be retrieved from the imported module.
+    """
+    if not isinstance(importable, str):
+        raise TypeError(f"Unhandled type of importable, val: {importable}")
+
+    def tryImport(module, fromlist):
+        pytype = importlib.import_module(module)
+        # Can have functions inside classes inside modules
+        for f in fromlist:
+            try:
+                pytype = getattr(pytype, f)
+            except AttributeError as e:
+                raise ImportError(f"Could not get attribute '{f}' from '{module}'")
+        return pytype
+
+    # Go through the import path attempting to load the module
+    # and retrieve the class or function as an attribute. Shift components
+    # from the module list to the attribute list until something works.
+    moduleComponents = importable.split(".")
+    infileComponents = []
+
+    while moduleComponents:
+        try:
+            pytype = tryImport(".".join(moduleComponents), infileComponents)
+            if not infileComponents and hasattr(pytype, moduleComponents[-1]):
+                # This module has an attribute with the same name as the
+                # module itself (like doImport.doImport, actually!).
+                # If that attribute was lifted to the package, we should
+                # return the attribute, not the module.
+                try:
+                    return tryImport(".".join(moduleComponents[:-1]), moduleComponents[-1:])
+                except ModuleNotFoundError:
+                    pass
+            return pytype
+        except ModuleNotFoundError:
+            # Move element from module to file and try again
+            infileComponents.insert(0, moduleComponents.pop())
+
+    raise ModuleNotFoundError(f"Unable to import {importable}")

tests/test_doImport.py

@@ -0,0 +1,67 @@
+# This file is part of daf_butler.
+#
+# Developed for the LSST Data Management System.
+# This product includes software developed by the LSST Project
+# (http://www.lsst.org).
+# See the COPYRIGHT file at the top-level directory of this distribution
+# for details of code ownership.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import unittest
+import inspect
+
+import lsst.utils.tests
+
+from lsst.utils import doImport
+
+
+class ImportTestCase(lsst.utils.tests.TestCase):
+    """Basic tests of doImport."""
+
+    def testDoImport(self):
+        c = doImport("lsst.utils.tests.TestCase")
+        self.assertEqual(c, lsst.utils.tests.TestCase)
+
+        c = doImport("lsst.utils.doImport")
+        self.assertEqual(type(c), type(doImport))
+        self.assertTrue(inspect.isfunction(c))
+
+        c = doImport("lsst.utils")
+        self.assertTrue(inspect.ismodule(c))
+
+        with self.assertRaises(ImportError):
+            doImport("lsst.utils.tests.TestCase.xyprint")
+
+        with self.assertRaises(ImportError):
+            doImport("lsst.utils.nothere")
+
+        with self.assertRaises(ModuleNotFoundError):
+            doImport("missing module")
+
+        with self.assertRaises(ModuleNotFoundError):
+            doImport("lsstdummy.import.fail")
+
+        with self.assertRaises(ImportError):
+            doImport("lsst.import.fail")
+
+        with self.assertRaises(ImportError):
+            doImport("lsst.utils.x")
+
+        with self.assertRaises(TypeError):
+            doImport([])
+
+
+if __name__ == "__main__":
+    unittest.main()