Revert to old behavior of Python expression; it is now again a TALES …

…expression (such that the pipe operator works as try-except).

CHANGES.rst

@@ -1,6 +1,17 @@
 Changes
 =======
 
+Features:
+
+- Python expression is now a TALES expression. That means that the
+  pipe operator can be used to chain two or more expressions in a
+  try-except sequence.
+
+  This behavior was ported from the 1.x series. Note that while it's
+  still possible to use the pipe character ("|") in an expression, it
+  must now be escaped.
+
+
 2.0-rc3 (2011-03-02)
 --------------------
 

src/chameleon/tales.py

@@ -213,20 +213,29 @@ def translate(self, expression, target):
             "can be devised.")
 
 
-class PythonExpr(object):
+class PythonExpr(TalesExpr):
     """Python expression compiler.
 
-    >>> test(PythonExpr('2+2'))
+    >>> test(PythonExpr('2 + 2'))
     4
+
+    The Python expression is a TALES expression. That means we can use
+    the pipe operator:
+
+    >>> test(PythonExpr('foo | 2 + 2 | 5'))
+    4
+
+    To include a pipe character, use a backslash escape sequence:
+
+    >>> test(PythonExpr('\"\|\"'))
+    '|'
+
     """
 
     transform = ItemLookupOnAttributeErrorVisitor(transform_attribute)
 
-    def __init__(self, expression):
-        self.expression = expression
-
-    def __call__(self, target, engine):
-        string = self.expression.strip().replace('\n', ' ')
+    def translate(self, expression, target):
+        string = expression.strip().replace('\n', ' ')
         decoded = decode_htmlentities(string)
 
         try: