Check argument type in Domain.project()

diff --git a/linpy/domains.py b/linpy/domains.py
index 31b5c3f..7015252 100644 (file)
--- a/linpy/domains.py
+++ b/linpy/domains.py
@@ -278,6 +278,10 @@ class Domain(GeometricObject):
         Project out the sequence of symbols given in arguments, and return the
         resulting domain.
         """
+        symbols = list(symbols)
+        for symbol in symbols:
+            if not isinstance(symbol, Symbol):
+                raise TypeError('symbols must be Symbol instances')
         islset = self._toislset(self.polyhedra, self.symbols)
         n = 0
         for index, symbol in reversed(list(enumerate(self.symbols))):