Backport PR #4372: Don't assume that SyntaxTB is always called with a SyntaxError

closes  #5184

IPython/core/tests/test_ultratb.py

@@ -138,3 +138,12 b' class SyntaxErrorTest(unittest.TestCase):'
             # The SyntaxError should point to the correct line
             with tt.AssertPrints(["7/", "SyntaxError"]):
                 ip.magic("run " + fname)
+
+    def test_non_syntaxerror(self):
+        # SyntaxTB may be called with an error other than a SyntaxError
+        # See e.g. gh-4361
+        try:
+            raise ValueError('QWERTY')
+        except ValueError:
+            with tt.AssertPrints('QWERTY'):
+                ip.showsyntaxerror()

IPython/core/ultratb.py

@@ -1198,7 +1198,8 b' class SyntaxTB(ListTB):'
         # If the source file has been edited, the line in the syntax error can
         # be wrong (retrieved from an outdated cache). This replaces it with
         # the current value.
-        if isinstance(value.filename, py3compat.string_types) \
+        if isinstance(value, SyntaxError) \
+                and isinstance(value.filename, py3compat.string_types) \
                 and isinstance(value.lineno, int):
             linecache.checkcache(value.filename)
             newtext = ulinecache.getline(value.filename, value.lineno)

IPython/testing/tools.py

@@ -363,6 +363,9 b' class AssertPrints(object):'
         setattr(sys, self.channel, self.buffer if self.suppress else self.tee)
     
     def __exit__(self, etype, value, traceback):
+        if value is not None:
+            # If an error was raised, don't check anything else
+            return False
         self.tee.flush()
         setattr(sys, self.channel, self.orig_stream)
         printed = self.buffer.getvalue()
@@ -381,6 +384,9 b' class AssertNotPrints(AssertPrints):'
     
     Counterpart of AssertPrints"""
     def __exit__(self, etype, value, traceback):
+        if value is not None:
+            # If an error was raised, don't check anything else
+            return False
         self.tee.flush()
         setattr(sys, self.channel, self.orig_stream)
         printed = self.buffer.getvalue()