print a better error for exceptions raised from inline snippets

beetsplug/inline.py

@@ -18,9 +18,19 @@ import logging
 import traceback
 
 from beets.plugins import BeetsPlugin
+from beets import ui
 
 log = logging.getLogger('beets')
 
+class InlineError(Exception):
+    """Raised when a runtime error occurs in an inline expression.
+    """
+    def __init__(self, expr, exc):
+        super(InlineError, self).__init__(
+            (u"error in inline path field expression:\n" \
+             u"%s\n%s: %s") % (expr, type(exc).__name__, unicode(exc))
+        )
+
 def compile_expr(expr):
     """Given a Python expression, compile it as a path field function.
     The returned function takes a single argument, an Item, and returns
@@ -35,7 +45,11 @@ def compile_expr(expr):
         return None
 
     def field_func(item):
-        return eval(code, dict(item.record))
+        values = dict(item.record)
+        try:
+            return eval(code, values)
+        except Exception, exc:
+            raise InlineError(expr, exc)
     return field_func
 
 class InlinePlugin(BeetsPlugin):

docs/changelog.rst

@@ -15,6 +15,8 @@ Changelog
   instead of 24.
 * The autotagger now also tolerates tracks whose track artists tags are set
   to "Various Artists".
+* The ``inline`` plugin now prints a more comprehensible error when exceptions
+  occur in Python snippets.
 * Fix a bug in the ``rewrite`` plugin that broke the use of multiple rules for
   a single field.
 * Fix a crash with non-ASCII characters in bytestring metadata fields (e.g.,