Source code for tornado.template

#!/usr/bin/env python
# Copyright 2009 Facebook
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

"""A simple template system that compiles templates to Python code.

Basic usage looks like::

    t = template.Template("<html>{{ myvalue }}</html>")
    print t.generate(myvalue="XXX")

`Loader` is a class that loads templates from a root directory and caches
the compiled templates::

    loader = template.Loader("/home/btaylor")
    print loader.load("test.html").generate(myvalue="XXX")

We compile all templates to raw Python. Error-reporting is currently... uh,
interesting. Syntax for the templates::

    ### base.html
        <title>{% block title %}Default title{% end %}</title>
          {% for student in students %}
            {% block student %}
              <li>{{ escape( }}</li>
            {% end %}
          {% end %}

    ### bold.html
    {% extends "base.html" %}

    {% block title %}A bolder title{% end %}

    {% block student %}
      <li><span style="bold">{{ escape( }}</span></li>
    {% end %}

Unlike most other template systems, we do not put any restrictions on the
expressions you can include in your statements. ``if`` and ``for`` blocks get
translated exactly into Python, so you can do complex expressions like::

   {% for student in [p for p in people if p.student and p.age > 23] %}
     <li>{{ escape( }}</li>
   {% end %}

Translating directly to Python means you can apply functions to expressions
easily, like the ``escape()`` function in the examples above. You can pass
functions in to your template just like any other variable
(In a `.RequestHandler`, override `.RequestHandler.get_template_namespace`)::

   ### Python code
   def add(x, y):
      return x + y

   ### The template
   {{ add(1, 2) }}

We provide the functions `escape() <.xhtml_escape>`, `.url_escape()`,
`.json_encode()`, and `.squeeze()` to all templates by default.

Typical applications do not create `Template` or `Loader` instances by
hand, but instead use the `~.RequestHandler.render` and
`~.RequestHandler.render_string` methods of
`tornado.web.RequestHandler`, which load templates automatically based
on the ``template_path`` `.Application` setting.

Variable names beginning with ``_tt_`` are reserved by the template
system and should not be used by application code.

Syntax Reference

Template expressions are surrounded by double curly braces: ``{{ ... }}``.
The contents may be any python expression, which will be escaped according
to the current autoescape setting and inserted into the output.  Other
template directives use ``{% %}``.  These tags may be escaped as ``{{!``
and ``{%!`` if you need to include a literal ``{{`` or ``{%`` in the output.

To comment out a section so that it is omitted from the output, surround it
with ``{# ... #}``.

``{% apply *function* %}...{% end %}``
    Applies a function to the output of all template code between ``apply``
    and ``end``::

        {% apply linkify %}{{name}} said: {{message}}{% end %}

    Note that as an implementation detail apply blocks are implemented
    as nested functions and thus may interact strangely with variables
    set via ``{% set %}``, or the use of ``{% break %}`` or ``{% continue %}``
    within loops.

``{% autoescape *function* %}``
    Sets the autoescape mode for the current file.  This does not affect
    other files, even those referenced by ``{% include %}``.  Note that
    autoescaping can also be configured globally, at the `.Application`
    or `Loader`.::

        {% autoescape xhtml_escape %}
        {% autoescape None %}

``{% block *name* %}...{% end %}``
    Indicates a named, replaceable block for use with ``{% extends %}``.
    Blocks in the parent template will be replaced with the contents of
    the same-named block in a child template.::

        <!-- base.html -->
        <title>{% block title %}Default title{% end %}</title>

        <!-- mypage.html -->
        {% extends "base.html" %}
        {% block title %}My page title{% end %}

``{% comment ... %}``
    A comment which will be removed from the template output.  Note that
    there is no ``{% end %}`` tag; the comment goes from the word ``comment``
    to the closing ``%}`` tag.

``{% extends *filename* %}``
    Inherit from another template.  Templates that use ``extends`` should
    contain one or more ``block`` tags to replace content from the parent
    template.  Anything in the child template not contained in a ``block``
    tag will be ignored.  For an example, see the ``{% block %}`` tag.

``{% for *var* in *expr* %}...{% end %}``
    Same as the python ``for`` statement.  ``{% break %}`` and
    ``{% continue %}`` may be used inside the loop.

``{% from *x* import *y* %}``
    Same as the python ``import`` statement.

``{% if *condition* %}...{% elif *condition* %}...{% else %}...{% end %}``
    Conditional statement - outputs the first section whose condition is
    true.  (The ``elif`` and ``else`` sections are optional)

``{% import *module* %}``
    Same as the python ``import`` statement.

``{% include *filename* %}``
    Includes another template file.  The included file can see all the local
    variables as if it were copied directly to the point of the ``include``
    directive (the ``{% autoescape %}`` directive is an exception).
    Alternately, ``{% module Template(filename, **kwargs) %}`` may be used
    to include another template with an isolated namespace.

``{% module *expr* %}``
    Renders a `~tornado.web.UIModule`.  The output of the ``UIModule`` is
    not escaped::

        {% module Template("foo.html", arg=42) %}

    ``UIModules`` are a feature of the `tornado.web.RequestHandler`
    class (and specifically its ``render`` method) and will not work
    when the template system is used on its own in other contexts.

``{% raw *expr* %}``
    Outputs the result of the given expression without autoescaping.

``{% set *x* = *y* %}``
    Sets a local variable.

``{% try %}...{% except %}...{% finally %}...{% else %}...{% end %}``
    Same as the python ``try`` statement.

``{% while *condition* %}... {% end %}``
    Same as the python ``while`` statement.  ``{% break %}`` and
    ``{% continue %}`` may be used inside the loop.

from __future__ import absolute_import, division, print_function, with_statement

import datetime
import linecache
import os.path
import posixpath
import re
import threading

from tornado import escape
from tornado.log import app_log
from tornado.util import bytes_type, ObjectDict, exec_in, unicode_type

    from cStringIO import StringIO  # py2
except ImportError:
    from io import StringIO  # py3

_DEFAULT_AUTOESCAPE = "xhtml_escape"
_UNSET = object()

[docs]class Template(object): """A compiled template. We compile into Python from the given template_string. You can generate the template from variables with generate(). """ # note that the constructor's signature is not extracted with # autodoc because _UNSET looks like garbage. When changing # this signature update website/sphinx/template.rst too. def __init__(self, template_string, name="<string>", loader=None, compress_whitespace=None, autoescape=_UNSET): = name if compress_whitespace is None: compress_whitespace = name.endswith(".html") or \ name.endswith(".js") if autoescape is not _UNSET: self.autoescape = autoescape elif loader: self.autoescape = loader.autoescape else: self.autoescape = _DEFAULT_AUTOESCAPE self.namespace = loader.namespace if loader else {} reader = _TemplateReader(name, escape.native_str(template_string)) self.file = _File(self, _parse(reader, self)) self.code = self._generate_python(loader, compress_whitespace) self.loader = loader try: # Under python2.5, the fake filename used here must match # the module name used in __name__ below. # The dont_inherit flag prevents's future imports # from being applied to the generated code. self.compiled = compile( escape.to_unicode(self.code), "" %'.', '_'), "exec", dont_inherit=True) except Exception: formatted_code = _format_code(self.code).rstrip() app_log.error("%s code:\n%s",, formatted_code) raise
[docs] def generate(self, **kwargs): """Generate this template with the given arguments.""" namespace = { "escape": escape.xhtml_escape, "xhtml_escape": escape.xhtml_escape, "url_escape": escape.url_escape, "json_encode": escape.json_encode, "squeeze": escape.squeeze, "linkify": escape.linkify, "datetime": datetime, "_tt_utf8": escape.utf8, # for internal use "_tt_string_types": (unicode_type, bytes_type), # __name__ and __loader__ allow the traceback mechanism to find # the generated source code. "__name__":'.', '_'), "__loader__": ObjectDict(get_source=lambda name: self.code), } namespace.update(self.namespace) namespace.update(kwargs) exec_in(self.compiled, namespace) execute = namespace["_tt_execute"] # Clear the traceback module's cache of source data now that # we've generated a new template (mainly for this module's # unittests, where different tests reuse the same name). linecache.clearcache() return execute()
def _generate_python(self, loader, compress_whitespace): buffer = StringIO() try: # named_blocks maps from names to _NamedBlock objects named_blocks = {} ancestors = self._get_ancestors(loader) ancestors.reverse() for ancestor in ancestors: ancestor.find_named_blocks(loader, named_blocks) writer = _CodeWriter(buffer, named_blocks, loader, ancestors[0].template, compress_whitespace) ancestors[0].generate(writer) return buffer.getvalue() finally: buffer.close() def _get_ancestors(self, loader): ancestors = [self.file] for chunk in self.file.body.chunks: if isinstance(chunk, _ExtendsBlock): if not loader: raise ParseError("{% extends %} block found, but no " "template loader") template = loader.load(, ancestors.extend(template._get_ancestors(loader)) return ancestors
[docs]class BaseLoader(object): """Base class for template loaders. You must use a template loader to use template constructs like ``{% extends %}`` and ``{% include %}``. The loader caches all templates after they are loaded the first time. """ def __init__(self, autoescape=_DEFAULT_AUTOESCAPE, namespace=None): """``autoescape`` must be either None or a string naming a function in the template namespace, such as "xhtml_escape". """ self.autoescape = autoescape self.namespace = namespace or {} self.templates = {} # self.lock protects self.templates. It's a reentrant lock # because templates may load other templates via `include` or # `extends`. Note that thanks to the GIL this code would be safe # even without the lock, but could lead to wasted work as multiple # threads tried to compile the same template simultaneously. self.lock = threading.RLock()
[docs] def reset(self): """Resets the cache of compiled templates.""" with self.lock: self.templates = {}
[docs] def resolve_path(self, name, parent_path=None): """Converts a possibly-relative path to absolute (used internally).""" raise NotImplementedError()
[docs] def load(self, name, parent_path=None): """Loads a template.""" name = self.resolve_path(name, parent_path=parent_path) with self.lock: if name not in self.templates: self.templates[name] = self._create_template(name) return self.templates[name]
def _create_template(self, name): raise NotImplementedError()
[docs]class Loader(BaseLoader): """A template loader that loads from a single root directory. """ def __init__(self, root_directory, **kwargs): super(Loader, self).__init__(**kwargs) self.root = os.path.abspath(root_directory) def resolve_path(self, name, parent_path=None): if parent_path and not parent_path.startswith("<") and \ not parent_path.startswith("/") and \ not name.startswith("/"): current_path = os.path.join(self.root, parent_path) file_dir = os.path.dirname(os.path.abspath(current_path)) relative_path = os.path.abspath(os.path.join(file_dir, name)) if relative_path.startswith(self.root): name = relative_path[len(self.root) + 1:] return name def _create_template(self, name): path = os.path.join(self.root, name) f = open(path, "rb") template = Template(, name=name, loader=self) f.close() return template
[docs]class DictLoader(BaseLoader): """A template loader that loads from a dictionary.""" def __init__(self, dict, **kwargs): super(DictLoader, self).__init__(**kwargs) self.dict = dict def resolve_path(self, name, parent_path=None): if parent_path and not parent_path.startswith("<") and \ not parent_path.startswith("/") and \ not name.startswith("/"): file_dir = posixpath.dirname(parent_path) name = posixpath.normpath(posixpath.join(file_dir, name)) return name def _create_template(self, name): return Template(self.dict[name], name=name, loader=self)
class _Node(object): def each_child(self): return () def generate(self, writer): raise NotImplementedError() def find_named_blocks(self, loader, named_blocks): for child in self.each_child(): child.find_named_blocks(loader, named_blocks) class _File(_Node): def __init__(self, template, body): self.template = template self.body = body self.line = 0 def generate(self, writer): writer.write_line("def _tt_execute():", self.line) with writer.indent(): writer.write_line("_tt_buffer = []", self.line) writer.write_line("_tt_append = _tt_buffer.append", self.line) self.body.generate(writer) writer.write_line("return _tt_utf8('').join(_tt_buffer)", self.line) def each_child(self): return (self.body,) class _ChunkList(_Node): def __init__(self, chunks): self.chunks = chunks def generate(self, writer): for chunk in self.chunks: chunk.generate(writer) def each_child(self): return self.chunks class _NamedBlock(_Node): def __init__(self, name, body, template, line): = name self.body = body self.template = template self.line = line def each_child(self): return (self.body,) def generate(self, writer): block = writer.named_blocks[] with writer.include(block.template, self.line): block.body.generate(writer) def find_named_blocks(self, loader, named_blocks): named_blocks[] = self _Node.find_named_blocks(self, loader, named_blocks) class _ExtendsBlock(_Node): def __init__(self, name): = name class _IncludeBlock(_Node): def __init__(self, name, reader, line): = name self.template_name = self.line = line def find_named_blocks(self, loader, named_blocks): included = loader.load(, self.template_name) included.file.find_named_blocks(loader, named_blocks) def generate(self, writer): included = writer.loader.load(, self.template_name) with writer.include(included, self.line): included.file.body.generate(writer) class _ApplyBlock(_Node): def __init__(self, method, line, body=None): self.method = method self.line = line self.body = body def each_child(self): return (self.body,) def generate(self, writer): method_name = "_tt_apply%d" % writer.apply_counter writer.apply_counter += 1 writer.write_line("def %s():" % method_name, self.line) with writer.indent(): writer.write_line("_tt_buffer = []", self.line) writer.write_line("_tt_append = _tt_buffer.append", self.line) self.body.generate(writer) writer.write_line("return _tt_utf8('').join(_tt_buffer)", self.line) writer.write_line("_tt_append(_tt_utf8(%s(%s())))" % ( self.method, method_name), self.line) class _ControlBlock(_Node): def __init__(self, statement, line, body=None): self.statement = statement self.line = line self.body = body def each_child(self): return (self.body,) def generate(self, writer): writer.write_line("%s:" % self.statement, self.line) with writer.indent(): self.body.generate(writer) # Just in case the body was empty writer.write_line("pass", self.line) class _IntermediateControlBlock(_Node): def __init__(self, statement, line): self.statement = statement self.line = line def generate(self, writer): # In case the previous block was empty writer.write_line("pass", self.line) writer.write_line("%s:" % self.statement, self.line, writer.indent_size() - 1) class _Statement(_Node): def __init__(self, statement, line): self.statement = statement self.line = line def generate(self, writer): writer.write_line(self.statement, self.line) class _Expression(_Node): def __init__(self, expression, line, raw=False): self.expression = expression self.line = line self.raw = raw def generate(self, writer): writer.write_line("_tt_tmp = %s" % self.expression, self.line) writer.write_line("if isinstance(_tt_tmp, _tt_string_types):" " _tt_tmp = _tt_utf8(_tt_tmp)", self.line) writer.write_line("else: _tt_tmp = _tt_utf8(str(_tt_tmp))", self.line) if not self.raw and writer.current_template.autoescape is not None: # In python3 functions like xhtml_escape return unicode, # so we have to convert to utf8 again. writer.write_line("_tt_tmp = _tt_utf8(%s(_tt_tmp))" % writer.current_template.autoescape, self.line) writer.write_line("_tt_append(_tt_tmp)", self.line) class _Module(_Expression): def __init__(self, expression, line): super(_Module, self).__init__("_tt_modules." + expression, line, raw=True) class _Text(_Node): def __init__(self, value, line): self.value = value self.line = line def generate(self, writer): value = self.value # Compress lots of white space to a single character. If the whitespace # breaks a line, have it continue to break a line, but just with a # single \n character if writer.compress_whitespace and "<pre>" not in value: value = re.sub(r"([\t ]+)", " ", value) value = re.sub(r"(\s*\n\s*)", "\n", value) if value: writer.write_line('_tt_append(%r)' % escape.utf8(value), self.line)
[docs]class ParseError(Exception): """Raised for template syntax errors.""" pass
class _CodeWriter(object): def __init__(self, file, named_blocks, loader, current_template, compress_whitespace): self.file = file self.named_blocks = named_blocks self.loader = loader self.current_template = current_template self.compress_whitespace = compress_whitespace self.apply_counter = 0 self.include_stack = [] self._indent = 0 def indent_size(self): return self._indent def indent(self): class Indenter(object): def __enter__(_): self._indent += 1 return self def __exit__(_, *args): assert self._indent > 0 self._indent -= 1 return Indenter() def include(self, template, line): self.include_stack.append((self.current_template, line)) self.current_template = template class IncludeTemplate(object): def __enter__(_): return self def __exit__(_, *args): self.current_template = self.include_stack.pop()[0] return IncludeTemplate() def write_line(self, line, line_number, indent=None): if indent is None: indent = self._indent line_comment = ' # %s:%d' % (, line_number) if self.include_stack: ancestors = ["%s:%d" % (, lineno) for (tmpl, lineno) in self.include_stack] line_comment += ' (via %s)' % ', '.join(reversed(ancestors)) print(" " * indent + line + line_comment, file=self.file) class _TemplateReader(object): def __init__(self, name, text): = name self.text = text self.line = 1 self.pos = 0 def find(self, needle, start=0, end=None): assert start >= 0, start pos = self.pos start += pos if end is None: index = self.text.find(needle, start) else: end += pos assert end >= start index = self.text.find(needle, start, end) if index != -1: index -= pos return index def consume(self, count=None): if count is None: count = len(self.text) - self.pos newpos = self.pos + count self.line += self.text.count("\n", self.pos, newpos) s = self.text[self.pos:newpos] self.pos = newpos return s def remaining(self): return len(self.text) - self.pos def __len__(self): return self.remaining() def __getitem__(self, key): if type(key) is slice: size = len(self) start, stop, step = key.indices(size) if start is None: start = self.pos else: start += self.pos if stop is not None: stop += self.pos return self.text[slice(start, stop, step)] elif key < 0: return self.text[key] else: return self.text[self.pos + key] def __str__(self): return self.text[self.pos:] def _format_code(code): lines = code.splitlines() format = "%%%dd %%s\n" % len(repr(len(lines) + 1)) return "".join([format % (i + 1, line) for (i, line) in enumerate(lines)]) def _parse(reader, template, in_block=None, in_loop=None): body = _ChunkList([]) while True: # Find next template directive curly = 0 while True: curly = reader.find("{", curly) if curly == -1 or curly + 1 == reader.remaining(): # EOF if in_block: raise ParseError("Missing {%% end %%} block for %s" % in_block) body.chunks.append(_Text(reader.consume(), reader.line)) return body # If the first curly brace is not the start of a special token, # start searching from the character after it if reader[curly + 1] not in ("{", "%", "#"): curly += 1 continue # When there are more than 2 curlies in a row, use the # innermost ones. This is useful when generating languages # like latex where curlies are also meaningful if (curly + 2 < reader.remaining() and reader[curly + 1] == '{' and reader[curly + 2] == '{'): curly += 1 continue break # Append any text before the special token if curly > 0: cons = reader.consume(curly) body.chunks.append(_Text(cons, reader.line)) start_brace = reader.consume(2) line = reader.line # Template directives may be escaped as "{{!" or "{%!". # In this case output the braces and consume the "!". # This is especially useful in conjunction with jquery templates, # which also use double braces. if reader.remaining() and reader[0] == "!": reader.consume(1) body.chunks.append(_Text(start_brace, line)) continue # Comment if start_brace == "{#": end = reader.find("#}") if end == -1: raise ParseError("Missing end expression #} on line %d" % line) contents = reader.consume(end).strip() reader.consume(2) continue # Expression if start_brace == "{{": end = reader.find("}}") if end == -1: raise ParseError("Missing end expression }} on line %d" % line) contents = reader.consume(end).strip() reader.consume(2) if not contents: raise ParseError("Empty expression on line %d" % line) body.chunks.append(_Expression(contents, line)) continue # Block assert start_brace == "{%", start_brace end = reader.find("%}") if end == -1: raise ParseError("Missing end block %%} on line %d" % line) contents = reader.consume(end).strip() reader.consume(2) if not contents: raise ParseError("Empty block tag ({%% %%}) on line %d" % line) operator, space, suffix = contents.partition(" ") suffix = suffix.strip() # Intermediate ("else", "elif", etc) blocks intermediate_blocks = { "else": set(["if", "for", "while", "try"]), "elif": set(["if"]), "except": set(["try"]), "finally": set(["try"]), } allowed_parents = intermediate_blocks.get(operator) if allowed_parents is not None: if not in_block: raise ParseError("%s outside %s block" % (operator, allowed_parents)) if in_block not in allowed_parents: raise ParseError("%s block cannot be attached to %s block" % (operator, in_block)) body.chunks.append(_IntermediateControlBlock(contents, line)) continue # End tag elif operator == "end": if not in_block: raise ParseError("Extra {%% end %%} block on line %d" % line) return body elif operator in ("extends", "include", "set", "import", "from", "comment", "autoescape", "raw", "module"): if operator == "comment": continue if operator == "extends": suffix = suffix.strip('"').strip("'") if not suffix: raise ParseError("extends missing file path on line %d" % line) block = _ExtendsBlock(suffix) elif operator in ("import", "from"): if not suffix: raise ParseError("import missing statement on line %d" % line) block = _Statement(contents, line) elif operator == "include": suffix = suffix.strip('"').strip("'") if not suffix: raise ParseError("include missing file path on line %d" % line) block = _IncludeBlock(suffix, reader, line) elif operator == "set": if not suffix: raise ParseError("set missing statement on line %d" % line) block = _Statement(suffix, line) elif operator == "autoescape": fn = suffix.strip() if fn == "None": fn = None template.autoescape = fn continue elif operator == "raw": block = _Expression(suffix, line, raw=True) elif operator == "module": block = _Module(suffix, line) body.chunks.append(block) continue elif operator in ("apply", "block", "try", "if", "for", "while"): # parse inner body recursively if operator in ("for", "while"): block_body = _parse(reader, template, operator, operator) elif operator == "apply": # apply creates a nested function so syntactically it's not # in the loop. block_body = _parse(reader, template, operator, None) else: block_body = _parse(reader, template, operator, in_loop) if operator == "apply": if not suffix: raise ParseError("apply missing method name on line %d" % line) block = _ApplyBlock(suffix, line, block_body) elif operator == "block": if not suffix: raise ParseError("block missing name on line %d" % line) block = _NamedBlock(suffix, block_body, template, line) else: block = _ControlBlock(contents, line, block_body) body.chunks.append(block) continue elif operator in ("break", "continue"): if not in_loop: raise ParseError("%s outside %s block" % (operator, set(["for", "while"]))) body.chunks.append(_Statement(contents, line)) continue else: raise ParseError("unknown operator: %r" % operator)