It seems to me you can't use ast.literal_eval()[1] to evaluate that kind of expression because it's just for literals[2].
Why don't you use eval()? [1] http://docs.python.org/2/library/ast.html#ast-helpers [2] http://docs.python.org/2/reference/lexical_analysis.html#literals ---------------------------------------- > To: python-list@python.org > From: fr...@chagford.com > Subject: Question about ast.literal_eval > Date: Mon, 20 May 2013 09:05:48 +0200 > > Hi all > > I am trying to emulate a SQL check constraint in Python. Quoting from > the PostgreSQL docs, "A check constraint is the most generic constraint > type. It allows you to specify that the value in a certain column must > satisfy a Boolean (truth-value) expression." > > The problem is that I want to store the constraint as a string, and I > was hoping to use ast.literal_eval to evaluate it, but it does not work. > >>>> x = 'abc' >>>> x in ('abc', xyz') > True >>>> b = "x in ('abc', 'xyz')" >>>> eval(b) > True >>>> from ast import literal_eval >>>> literal_eval(b) > ValueError: malformed node or string: <_ast.Compare object at ...> > > Is there a safe way to do what I want? I am using python 3.3. > > Thanks > > Frank Millman > > -- > http://mail.python.org/mailman/listinfo/python-list > -- http://mail.python.org/mailman/listinfo/python-list
