How to use the mako.compat.exception_as function in Mako

def _lookup_template(context, uri, relativeto):
    lookup = context._with_template.lookup
    if lookup is None:
        raise exceptions.TemplateLookupException(
            "Template '%s' has no TemplateLookup associated" %
            context._with_template.uri)
    uri = lookup.adjust_uri(uri, relativeto)
    try:
        return lookup.get_template(uri)
    except exceptions.TopLevelLookupException:
        raise exceptions.TemplateLookupException(str(compat.exception_as()))

def _exec_template(callable_, context, args=None, kwargs=None):
    """execute a rendering callable given the callable, a
    Context, and optional explicit arguments

    the contextual Template will be located if it exists, and
    the error handling options specified on that Template will
    be interpreted here.
    """
    template = context._with_template
    if template is not None and \
            (template.format_exceptions or template.error_handler):
        try:
            callable_(context, *args, **kwargs)
        except Exception:
            _render_error(template, context, compat.exception_as())
        except:
            e = sys.exc_info()[0]
            _render_error(template, context, e)
    else:
        callable_(context, *args, **kwargs)

def _lookup_template(context, uri, relativeto):
    lookup = context._with_template.lookup
    if lookup is None:
        raise exceptions.TemplateLookupException(
            "Template '%s' has no TemplateLookup associated"
            % context._with_template.uri
        )
    uri = lookup.adjust_uri(uri, relativeto)
    try:
        return lookup.get_template(uri)
    except exceptions.TopLevelLookupException:
        raise exceptions.TemplateLookupException(str(compat.exception_as()))

def _include_file(context, uri, calling_uri, **kwargs):
    """locate the template from the given uri and include it in
    the current output."""

    template = _lookup_template(context, uri, calling_uri)
    (callable_, ctx) = _populate_self_namespace(
        context._clean_inheritance_tokens(), template
    )
    kwargs = _kwargs_for_include(callable_, context._data, **kwargs)
    if template.include_error_handler:
        try:
            callable_(ctx, **kwargs)
        except Exception:
            result = template.include_error_handler(ctx, compat.exception_as())
            if not result:
                compat.reraise(*sys.exc_info())
    else:
        callable_(ctx, **kwargs)

def _exec_template(callable_, context, args=None, kwargs=None):
    """execute a rendering callable given the callable, a
    Context, and optional explicit arguments

    the contextual Template will be located if it exists, and
    the error handling options specified on that Template will
    be interpreted here.
    """
    template = context._with_template
    if template is not None and (
        template.format_exceptions or template.error_handler
    ):
        try:
            callable_(context, *args, **kwargs)
        except Exception:
            _render_error(template, context, compat.exception_as())
        except:
            e = sys.exc_info()[0]
            _render_error(template, context, e)
    else:
        callable_(context, *args, **kwargs)

def parse(code, mode="exec", **exception_kwargs):
    """Parse an expression into AST"""

    try:
        return _ast_util.parse(code, "", mode)
    except Exception:
        raise exceptions.SyntaxException(
            "(%s) %s (%r)"
            % (
                compat.exception_as().__class__.__name__,
                compat.exception_as(),
                code[0:50],
            ),
            **exception_kwargs
        )

def _exec_template(callable_, context, args=None, kwargs=None):
    """execute a rendering callable given the callable, a
    Context, and optional explicit arguments

    the contextual Template will be located if it exists, and
    the error handling options specified on that Template will
    be interpreted here.
    """
    template = context._with_template
    if template is not None and (
        template.format_exceptions or template.error_handler
    ):
        try:
            callable_(context, *args, **kwargs)
        except Exception:
            _render_error(template, context, compat.exception_as())
        except:
            e = sys.exc_info()[0]
            _render_error(template, context, e)
    else:
        callable_(context, *args, **kwargs)

def _exec_template(callable_, context, args=None, kwargs=None):
    """execute a rendering callable given the callable, a
    Context, and optional explicit arguments

    the contextual Template will be located if it exists, and
    the error handling options specified on that Template will
    be interpreted here.
    """
    template = context._with_template
    if template is not None and \
            (template.format_exceptions or template.error_handler):
        try:
            callable_(context, *args, **kwargs)
        except Exception:
            _render_error(template, context, compat.exception_as())
        except:
            e = sys.exc_info()[0]
            _render_error(template, context, e)
    else:
        callable_(context, *args, **kwargs)

def _exec_template(callable_, context, args=None, kwargs=None):
    """execute a rendering callable given the callable, a
    Context, and optional explicit arguments

    the contextual Template will be located if it exists, and
    the error handling options specified on that Template will
    be interpreted here.
    """
    template = context._with_template
    if template is not None and \
            (template.format_exceptions or template.error_handler):
        try:
            callable_(context, *args, **kwargs)
        except Exception:
            _render_error(template, context, compat.exception_as())
        except:
            e = sys.exc_info()[0]
            _render_error(template, context, e)
    else:
        callable_(context, *args, **kwargs)