pdb: allow for --pdbclass=mod:attr.class

changelog/4855.feature.rst

@@ -0,0 +1,4 @@
+The ``--pdbcls`` option handles classes via module attributes now (e.g.
+``pdb:pdb.Pdb`` with `pdb++`_), and its validation was improved.
+
+.. _pdb++: https://pypi.org/project/pdbpp/

src/_pytest/debugging.py

@@ -12,25 +12,32 @@
 from _pytest.config import hookimpl
 
 
-def pytest_addoption(parser):
-    def validate_usepdb_cls(value):
-        try:
-            modname, classname = value.split(":")
-        except ValueError:
-            raise argparse.ArgumentTypeError(
-                "{!r} is not in the format 'modname:classname'".format(value)
-            )
-
-        try:
-            __import__(modname)
-            pdb_cls = getattr(sys.modules[modname], classname)
-        except Exception as exc:
-            raise argparse.ArgumentTypeError(
-                "could not get pdb class for {!r}: {}".format(value, exc)
-            )
+def _validate_usepdb_cls(value):
+    try:
+        modname, classname = value.split(":")
+    except ValueError:
+        raise argparse.ArgumentTypeError(
+            "{!r} is not in the format 'modname:classname'".format(value)
+        )
+
+    try:
+        __import__(modname)
+        mod = sys.modules[modname]
+
+        # Handle --pdbcls=pdb:pdb.Pdb (useful e.g. with pdbpp).
+        parts = classname.split(".")
+        pdb_cls = getattr(mod, parts[0])
+        for part in parts[1:]:
+            pdb_cls = getattr(pdb_cls, part)
 
         return pdb_cls
+    except Exception as exc:
+        raise argparse.ArgumentTypeError(
+            "could not get pdb class for {!r}: {}".format(value, exc)
+        )
+
 
+def pytest_addoption(parser):
     group = parser.getgroup("general")
     group._addoption(
         "--pdb",
@@ -42,7 +49,7 @@ def validate_usepdb_cls(value):
         "--pdbcls",
         dest="usepdb_cls",
         metavar="modulename:classname",
-        type=validate_usepdb_cls,
+        type=_validate_usepdb_cls,
         help="start a custom interactive Python debugger on errors. "
         "For example: --pdbcls=IPython.terminal.debugger:TerminalPdb",
     )

testing/test_pdb.py

@@ -2,12 +2,14 @@
 from __future__ import division
 from __future__ import print_function
 
+import argparse
 import os
 import platform
 import sys
 
 import _pytest._code
 import pytest
+from _pytest.debugging import _validate_usepdb_cls
 
 try:
     breakpoint
@@ -695,12 +697,15 @@ def test_pdb_custom_cls_invalid(self, testdir):
                 "*: error: argument --pdbcls: 'invalid' is not in the format 'modname:classname'"
             ]
         )
-        result = testdir.runpytest_inprocess("--pdbcls=pdb:DoesNotExist")
-        result.stderr.fnmatch_lines(
-            [
-                "*: error: argument --pdbcls: could not get pdb class for 'pdb:DoesNotExist':*"
-            ]
-        )
+
+    def test_pdb_validate_usepdb_cls(self, testdir):
+        assert _validate_usepdb_cls("os.path:dirname.__name__") == "dirname"
+
+        with pytest.raises(
+            argparse.ArgumentTypeError,
+            match=r"^could not get pdb class for 'pdb:DoesNotExist': .*'DoesNotExist'",
+        ):
+            _validate_usepdb_cls("pdb:DoesNotExist")
 
     def test_pdb_custom_cls_without_pdb(self, testdir, custom_pdb_calls):
         p1 = testdir.makepyfile("""xxx """)