Source code for zope.tales.pythonexpr

##############################################################################
#
# Copyright (c) 2001, 2002 Zope Foundation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE.
#
##############################################################################
"""Generic Python Expression Handler
"""
import types




class PythonExpr:
    """
    Evaluates a python expression by calling :func:`eval` after
    compiling it with :func:`compile`.
    """
    def __init__(self, name, expr, engine):
        """
        :param str expr: The Python expression.
        :param ExpressionEngine engine: The expression compiler that
            is creating us.
        """
        text = '\n'.join(expr.splitlines())  # normalize line endings
        text = '(' + text + ')'  # Put text in parens so newlines don't matter
        self.text = text
        try:
            code = self._compile(text, '<string>')
        except SyntaxError as e:
            raise engine.getCompilerError()(str(e))
        self._code = code
        self._varnames = code.co_names
        # Variables used inside list comprehensions are not
        # directly available via co_names.
        for const in code.co_consts:
            if isinstance(const, types.CodeType):
                self._varnames += const.co_names

    def _compile(self, text, filename):
        return compile(text, filename, 'eval')

    def _bind_used_names(self, econtext, builtins):
        # Construct a dictionary of globals with which the Python
        # expression should be evaluated.
        names = {}
        vars = econtext.vars
        marker = self
        if not isinstance(builtins, dict):
            builtins = builtins.__dict__
        for vname in self._varnames:
            val = vars.get(vname, marker)
            if val is not marker:
                names[vname] = val
            elif vname not in builtins:
                # Fall back to using expression types as variable values.
                val = econtext._engine.getTypes().get(vname, marker)
                if val is not marker:
                    val = ExprTypeProxy(vname, val, econtext)
                    names[vname] = val

        names['__builtins__'] = builtins
        return names

    def __call__(self, econtext):
        __traceback_info__ = self.text
        vars = self._bind_used_names(econtext, __builtins__)
        return eval(self._code, vars)

    def __str__(self):
        return 'Python expression "%s"' % self.text

    def __repr__(self):
        return '<PythonExpr %s>' % self.text



class ExprTypeProxy:
    '''Class that proxies access to an expression type handler'''
    def __init__(self, name, handler, econtext):
        self._name = name
        self._handler = handler
        self._econtext = econtext

    def __call__(self, text):
        return self._handler(self._name, text,
                             self._econtext._engine)(self._econtext)