Environment.py 文件源码

def __setitem__(self, key, value):
        # This is heavily used.  This implementation is the best we have
        # according to the timings in bench/env.__setitem__.py.
        #
        # The "key in self._special_set_keys" test here seems to perform
        # pretty well for the number of keys we have.  A hard-coded
        # list works a little better in Python 2.5, but that has the
        # disadvantage of maybe getting out of sync if we ever add more
        # variable names.  Using self._special_set.has_key() works a
        # little better in Python 2.4, but is worse than this test.
        # So right now it seems like a good trade-off, but feel free to
        # revisit this with bench/env.__setitem__.py as needed (and
        # as newer versions of Python come out).
        if key in self._special_set_keys:
            self._special_set[key](self, key, value)
        else:
            # If we already have the entry, then it's obviously a valid
            # key and we don't need to check.  If we do check, using a
            # global, pre-compiled regular expression directly is more
            # efficient than calling another function or a method.
            if key not in self._dict \
               and not _is_valid_var.match(key):
                    raise SCons.Errors.UserError("Illegal construction variable `%s'" % key)
            self._dict[key] = value