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#!/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, 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::
### Python code
def add(x, y):
return x + y
### The template
{{ add(1, 2) }}
We provide the functions 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 `render` and `render_string` methods of
`tornado.web.RequestHandler`, which load templates automatically based
on the ``template_path`` `Application` setting.
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 %}
``{% 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.
``{% 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) %}
``{% 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.
from __future__ import absolute_import, division, with_statement
import cStringIO
import datetime
import linecache
import logging
import os.path
import posixpath
import re
import threading
from tornado import escape
from tornado.util import bytes_type, ObjectDict
_DEFAULT_AUTOESCAPE = "xhtml_escape"
_UNSET = object()
class Template(object):
"""A compiled template.
We compile into Python from the given template_string. You can generate
the template from variables with generate().
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 \
if autoescape is not _UNSET:
self.autoescape = autoescape
elif loader:
self.autoescape = loader.autoescape
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
# Under python2.5, the fake filename used here must match
# the module name used in __name__ below.
self.compiled = compile(
"" %'.', '_'),
except Exception:
formatted_code = _format_code(self.code).rstrip()
logging.error("%s code:\n%s",, formatted_code)
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,
"_utf8": escape.utf8, # for internal use
"_string_types": (unicode, bytes_type),
# __name__ and __loader__ allow the traceback mechanism to find
# the generated source code.
"__name__":'.', '_'),
"__loader__": ObjectDict(get_source=lambda name: self.code),
exec self.compiled in namespace
execute = namespace["_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).
return execute()
except Exception:
formatted_code = _format_code(self.code).rstrip()
logging.error("%s code:\n%s",, formatted_code)
def _generate_python(self, loader, compress_whitespace):
buffer = cStringIO.StringIO()
# named_blocks maps from names to _NamedBlock objects
named_blocks = {}
ancestors = self._get_ancestors(loader)
for ancestor in ancestors:
ancestor.find_named_blocks(loader, named_blocks)
self.file.find_named_blocks(loader, named_blocks)
writer = _CodeWriter(buffer, named_blocks, loader, ancestors[0].template,
return buffer.getvalue()
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(,
return ancestors
class BaseLoader(object):
"""Base class for template loaders."""
def __init__(self, autoescape=_DEFAULT_AUTOESCAPE, namespace=None):
"""Creates a template loader.
root_directory may be the empty string if this loader does not
use the filesystem.
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()
def reset(self):
"""Resets the cache of compiled templates."""
with self.lock:
self.templates = {}
def resolve_path(self, name, parent_path=None):
"""Converts a possibly-relative path to absolute (used internally)."""
raise NotImplementedError()
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()
class Loader(BaseLoader):
"""A template loader that loads from a single root directory.
You must use a template loader to use template constructs like
{% extends %} and {% include %}. Loader caches all templates after
they are loaded the first time.
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)
return template
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 _execute():", self.line)
with writer.indent():
writer.write_line("_buffer = []", self.line)
writer.write_line("_append = _buffer.append", self.line)
writer.write_line("return _utf8('').join(_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:
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):
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):
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 = "apply%d" % writer.apply_counter
writer.apply_counter += 1
writer.write_line("def %s():" % method_name, self.line)
with writer.indent():
writer.write_line("_buffer = []", self.line)
writer.write_line("_append = _buffer.append", self.line)
writer.write_line("return _utf8('').join(_buffer)", self.line)
writer.write_line("_append(%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():
class _IntermediateControlBlock(_Node):
def __init__(self, statement, line):
self.statement = statement
self.line = line
def generate(self, writer):
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("_tmp = %s" % self.expression, self.line)
writer.write_line("if isinstance(_tmp, _string_types):"
" _tmp = _utf8(_tmp)", self.line)
writer.write_line("else: _tmp = _utf8(str(_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("_tmp = _utf8(%s(_tmp))" %
writer.current_template.autoescape, self.line)
writer.write_line("_append(_tmp)", self.line)
class _Module(_Expression):
def __init__(self, expression, line):
super(_Module, self).__init__("_modules." + expression, line,
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('_append(%r)' % escape.utf8(value), self.line)
class ParseError(Exception):
"""Raised for template syntax errors."""
class _CodeWriter(object):
def __init__(self, file, named_blocks, loader, current_template,
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 == 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 >> self.file, " " * indent + line + line_comment
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)
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
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]
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):
body = _ChunkList([])
while True:
# Find next template directive
curly = 0
while True:
curly = reader.find("{", curly)
if curly == -1 or curly + 1 == reader.remaining():
if in_block:
raise ParseError("Missing {%% end %%} block for %s" %
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
# 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
# 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] == "!":
body.chunks.append(_Text(start_brace, line))
# Comment
if start_brace == "{#":
end = reader.find("#}")
if end == -1:
raise ParseError("Missing end expression #} on line %d" % line)
contents = reader.consume(end).strip()
# Expression
if start_brace == "{{":
end = reader.find("}}")
if end == -1:
raise ParseError("Missing end expression }} on line %d" % line)
contents = reader.consume(end).strip()
if not contents:
raise ParseError("Empty expression on line %d" % line)
body.chunks.append(_Expression(contents, line))
# 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()
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))
# 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":
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
elif operator == "raw":
block = _Expression(suffix, line, raw=True)
elif operator == "module":
block = _Module(suffix, line)
elif operator in ("apply", "block", "try", "if", "for", "while"):
# parse inner body recursively
block_body = _parse(reader, template, operator)
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)
block = _ControlBlock(contents, line, block_body)
raise ParseError("unknown operator: %r" % operator)