Call repr() when pretty() fails in _pprint_displayhook

news/print-mocks-correctly.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* Viewing mock objects in the shell
+
+**Security:**
+
+* <news item>

xonsh/main.py

@@ -251,9 +251,11 @@ def _pprint_displayhook(value):
         builtins._ = value
         return
     env = builtins.__xonsh__.env
+    printed_val = None
     if env.get("PRETTY_PRINT_RESULTS"):
         printed_val = pretty(value)
-    else:
+    if not isinstance(printed_val, str):
+        # pretty may fail (i.e for unittest.mock.Mock)
         printed_val = repr(value)
     if HAS_PYGMENTS and env.get("COLOR_RESULTS"):
         tokens = list(pygments.lex(printed_val, lexer=pyghooks.XonshLexer()))