from ast import literal_eval from itertools import chain from itertools import islice from . import nodes from ._compat import text_type from .compiler import CodeGenerator from .compiler import has_safe_repr from .environment import Environment from .environment import Template def native_concat(nodes): """Return a native Python type from the list of compiled nodes. If the result is a single node, its value is returned. Otherwise, the nodes are concatenated as strings. If the result can be parsed with :func:`ast.literal_eval`, the parsed value is returned. Otherwise, the string is returned. :param nodes: Iterable of nodes to concatenate. """ head = list(islice(nodes, 2)) if not head: return None if len(head) == 1: raw = head[0] else: raw = u"".join([text_type(v) for v in chain(head, nodes)]) try: return literal_eval(raw) except (ValueError, SyntaxError, MemoryError): return raw class NativeCodeGenerator(CodeGenerator): """A code generator which renders Python types by not adding ``to_string()`` around output nodes. """ @staticmethod def _default_finalize(value): return value def _output_const_repr(self, group): return repr(u"".join([text_type(v) for v in group])) def _output_child_to_const(self, node, frame, finalize): const = node.as_const(frame.eval_ctx) if not has_safe_repr(const): raise nodes.Impossible() if isinstance(node, nodes.TemplateData): return const return finalize.const(const) def _output_child_pre(self, node, frame, finalize): if finalize.src is not None: self.write(finalize.src) def _output_child_post(self, node, frame, finalize): if finalize.src is not None: self.write(")") class NativeEnvironment(Environment): """An environment that renders templates to native Python types.""" code_generator_class = NativeCodeGenerator class NativeTemplate(Template): environment_class = NativeEnvironment def render(self, *args, **kwargs): """Render the template to produce a native Python type. If the result is a single node, its value is returned. Otherwise, the nodes are concatenated as strings. If the result can be parsed with :func:`ast.literal_eval`, the parsed value is returned. Otherwise, the string is returned. """ vars = dict(*args, **kwargs) try: return native_concat(self.root_render_func(self.new_context(vars))) except Exception: return self.environment.handle_exception() NativeEnvironment.template_class = NativeTemplate