Add exception errors file

compiler/base/errors.py

@@ -0,0 +1,15 @@
+
+
+class drc_error(Exception):
+    """Exception raised for DRC errors.
+
+    Attributes:
+        expression -- input expression in which the error occurred
+        message -- explanation of the error
+    """
+
+    # def __init__(self, expression, message):
+    #     self.expression = expression
+    #     self.message = message
+    def __init__(self, message):
+        self.message = message