Only recognize the expected output as an exception if it *starts* with

a traceback message.  I.e., examples that raise exceptions may no
longer generate pre-exception output.  This restores the behavior of
doctest in python 2.3.  The ability to check pre-exception output is
being removed because it makes the documentation simpler; and because
there are very few use cases for it.

2 files changed, 21 insertions, 15 deletions

diff --git a/Lib/doctest.py b/Lib/doctest.py
index 43f21b2..01f7cb3 100644
--- a/Lib/doctest.py
+++ b/Lib/doctest.py
@@ -1281,15 +1281,14 @@ class DocTestRunner:
 
     # A regular expression for handling `want` strings that contain
     # expected exceptions.  It divides `want` into three pieces:
-    #    - the pre-exception output (`want`)
     #    - the traceback header line (`hdr`)
+    #    - the traceback stack (`stack`)
     #    - the exception message (`msg`), as generated by
     #      traceback.format_exception_only()
     # `msg` may have multiple lines.  We assume/require that the
     # exception message is the first non-indented line starting with a word
     # character following the traceback header line.
     _EXCEPTION_RE = re.compile(r"""
-        (?P<want> .*?)   # suck up everything until traceback header
         # Grab the traceback header.  Different versions of Python have
         # said different things on the first traceback line.
         ^(?P<hdr> Traceback\ \(
@@ -1297,9 +1296,9 @@ class DocTestRunner:
             |   innermost\ last
             ) \) :
         )
-        \s* $  # toss trailing whitespace on traceback header
-        .*?    # don't blink:  absorb stuff until a line *starts* with \w
-        ^ (?P<msg> \w+ .*)
+        \s* $                # toss trailing whitespace on the header.
+        (?P<stack> .*?)      # don't blink: absorb stuff until...
+        ^ (?P<msg> \w+ .*)   #     a line *starts* with alphanum.
         """, re.VERBOSE | re.MULTILINE | re.DOTALL)
 
     def __run(self, test, compileflags, out):
@@ -1374,13 +1373,10 @@ class DocTestRunner:
                                                      exc_info)
                     failures += 1
                 else:
-                    e_want, e_msg = m.group('want', 'msg')
-                    # The test passes iff the pre-exception output and
-                    # the exception description match the values given
-                    # in `want`.
-                    if (self._checker.check_output(e_want, got,
-                                                   self.optionflags) and
-                        self._checker.check_output(e_msg, exc_msg,
+                    # The test passes iff the expected exception
+                    # message (`m.group('msg')`) matches the actual
+                    # exception message (`exc_msg`).
+                    if (self._checker.check_output(m.group('msg'), exc_msg,
                                                    self.optionflags)):
                         self.report_success(out, test, example,
                                        got + _exception_traceback(exc_info))
diff --git a/Lib/test/test_doctest.py b/Lib/test/test_doctest.py
index d5e9ef5..5d0cf90 100644
--- a/Lib/test/test_doctest.py
+++ b/Lib/test/test_doctest.py
@@ -623,8 +623,10 @@ replaced with any other string:
     >>> doctest.DocTestRunner(verbose=False).run(test)
     (0, 2)
 
-An example may generate output before it raises an exception; if it
-does, then the output must match the expected output:
+An example may not generate output before it raises an exception; if
+it does, then the traceback message will not be recognized as
+signaling an expected exception, so the example will be reported as an
+unexpected exception:
 
     >>> def f(x):
     ...     '''
@@ -636,7 +638,15 @@ does, then the output must match the expected output:
     ...     '''
     >>> test = doctest.DocTestFinder().find(f)[0]
     >>> doctest.DocTestRunner(verbose=False).run(test)
-    (0, 2)
+    ... # doctest: +ELLIPSIS
+    **********************************************************************
+    Line 3, in f
+    Failed example:
+        print 'pre-exception output', x/0
+    Exception raised:
+        ...
+        ZeroDivisionError: integer division or modulo by zero
+    (1, 2)
 
 Exception messages may contain newlines: