src/templating.py
templating.py
Official Document
Implements the bridge to Jinja2.
Overview
This module is provides some convenient methods to use Jinja2 template system. To understand what is a template system, click here to take a look at Jinja2 documentation. Simply speaking, you can treat a template system as a black box, and it takes a string or a file as input, and it generates a rendered string based on some specific rules. For Flask, in most cases, a rendered string is a piece of HTML code.
Details
_default_template_ctx_processor
The method _default_template_ctx_processor returns a dict which contains g, request, and session of the current request and the current app.
def _default_template_ctx_processor():
reqctx = _request_ctx_stack.top
appctx = _app_ctx_stack.top
rv = {}
if appctx is not None:
rv["g"] = appctx.g
if reqctx is not None:
rv["request"] = reqctx.request
rv["session"] = reqctx.session
return rv
Environment
The class Environment is a simple subclass of jinja2.Environment, and it has same functions of jinja2.Environment except for a special loader which is added in the constructor.
from jinja2 import Environment as BaseEnvironment
class Environment(BaseEnvironment):
def __init__(self, app, **options):
if "loader" not in options:
options["loader"] = app.create_global_jinja_loader()
BaseEnvironment.__init__(self, **options)
self.app = app
DispatchingJinjaLoader
The class DispatchingJinjaLoader is a subclass of jinja2.BaseLoader, and it implements the template loading logic of Flask.
class DispatchingJinjaLoader(BaseLoader):
"""A loader that looks for templates in the application and all
the blueprint folders.
"""
def __init__(self, app):
self.app = app
def get_source(self, environment, template):
if self.app.config["EXPLAIN_TEMPLATE_LOADING"]:
return self._get_source_explained(environment, template)
return self._get_source_fast(environment, template)
def _get_source_explained(self, environment, template):
attempts = []
trv = None
for srcobj, loader in self._iter_loaders(template):
try:
rv = loader.get_source(environment, template)
if trv is None:
trv = rv
except TemplateNotFound:
rv = None
attempts.append((loader, srcobj, rv))
from .debughelpers import explain_template_loading_attempts
explain_template_loading_attempts(self.app, template, attempts)
if trv is not None:
return trv
raise TemplateNotFound(template)
def _get_source_fast(self, environment, template):
for _srcobj, loader in self._iter_loaders(template):
try:
return loader.get_source(environment, template)
except TemplateNotFound:
continue
raise TemplateNotFound(template)
def _iter_loaders(self, template):
loader = self.app.jinja_loader
if loader is not None:
yield self.app, loader
for blueprint in self.app.iter_blueprints():
loader = blueprint.jinja_loader
if loader is not None:
yield blueprint, loader
def list_templates(self):
result = set()
loader = self.app.jinja_loader
if loader is not None:
result.update(loader.list_templates())
for blueprint in self.app.iter_blueprints():
loader = blueprint.jinja_loader
if loader is not None:
for template in loader.list_templates():
result.add(template)
return list(result)
_render
The method _render renders the template, and fires the signals before and after the process.
def _render(template, context, app):
before_render_template.send(app, template=template, context=context)
rv = template.render(context)
template_rendered.send(app, template=template, context=context)
return rv
render_template
The method render_template renders a template from the template folder with the given context, and this is a “public” method which can be used outside this module.
def render_template(template_name_or_list, **context):
ctx = _app_ctx_stack.top
ctx.app.update_template_context(context)
return _render(
ctx.app.jinja_env.get_or_select_template(template_name_or_list),
context,
ctx.app,
)
render_template_string
The method render_template_string renders a template from the given string.
def render_template_string(source, **context):
ctx = _app_ctx_stack.top
ctx.app.update_template_context(context)
return _render(ctx.app.jinja_env.from_string(source), context, ctx.app)
Source Code
# -*- coding: utf-8 -*-
"""
flask.templating
~~~~~~~~~~~~~~~~
Implements the bridge to Jinja2.
:copyright: 2010 Pallets
:license: BSD-3-Clause
"""
from jinja2 import BaseLoader
from jinja2 import Environment as BaseEnvironment
from jinja2 import TemplateNotFound
from .globals import _app_ctx_stack
from .globals import _request_ctx_stack
from .signals import before_render_template
from .signals import template_rendered
def _default_template_ctx_processor():
"""Default template context processor. Injects `request`,
`session` and `g`.
"""
reqctx = _request_ctx_stack.top
appctx = _app_ctx_stack.top
rv = {}
if appctx is not None:
rv["g"] = appctx.g
if reqctx is not None:
rv["request"] = reqctx.request
rv["session"] = reqctx.session
return rv
class Environment(BaseEnvironment):
"""Works like a regular Jinja2 environment but has some additional
knowledge of how Flask's blueprint works so that it can prepend the
name of the blueprint to referenced templates if necessary.
"""
def __init__(self, app, **options):
if "loader" not in options:
options["loader"] = app.create_global_jinja_loader()
BaseEnvironment.__init__(self, **options)
self.app = app
class DispatchingJinjaLoader(BaseLoader):
"""A loader that looks for templates in the application and all
the blueprint folders.
"""
def __init__(self, app):
self.app = app
def get_source(self, environment, template):
if self.app.config["EXPLAIN_TEMPLATE_LOADING"]:
return self._get_source_explained(environment, template)
return self._get_source_fast(environment, template)
def _get_source_explained(self, environment, template):
attempts = []
trv = None
for srcobj, loader in self._iter_loaders(template):
try:
rv = loader.get_source(environment, template)
if trv is None:
trv = rv
except TemplateNotFound:
rv = None
attempts.append((loader, srcobj, rv))
from .debughelpers import explain_template_loading_attempts
explain_template_loading_attempts(self.app, template, attempts)
if trv is not None:
return trv
raise TemplateNotFound(template)
def _get_source_fast(self, environment, template):
for _srcobj, loader in self._iter_loaders(template):
try:
return loader.get_source(environment, template)
except TemplateNotFound:
continue
raise TemplateNotFound(template)
def _iter_loaders(self, template):
loader = self.app.jinja_loader
if loader is not None:
yield self.app, loader
for blueprint in self.app.iter_blueprints():
loader = blueprint.jinja_loader
if loader is not None:
yield blueprint, loader
def list_templates(self):
result = set()
loader = self.app.jinja_loader
if loader is not None:
result.update(loader.list_templates())
for blueprint in self.app.iter_blueprints():
loader = blueprint.jinja_loader
if loader is not None:
for template in loader.list_templates():
result.add(template)
return list(result)
def _render(template, context, app):
"""Renders the template and fires the signal"""
before_render_template.send(app, template=template, context=context)
rv = template.render(context)
template_rendered.send(app, template=template, context=context)
return rv
def render_template(template_name_or_list, **context):
"""Renders a template from the template folder with the given
context.
:param template_name_or_list: the name of the template to be
rendered, or an iterable with template names
the first one existing will be rendered
:param context: the variables that should be available in the
context of the template.
"""
ctx = _app_ctx_stack.top
ctx.app.update_template_context(context)
return _render(
ctx.app.jinja_env.get_or_select_template(template_name_or_list),
context,
ctx.app,
)
def render_template_string(source, **context):
"""Renders a template from the given template source string
with the given context. Template variables will be autoescaped.
:param source: the source code of the template to be
rendered
:param context: the variables that should be available in the
context of the template.
"""
ctx = _app_ctx_stack.top
ctx.app.update_template_context(context)
return _render(ctx.app.jinja_env.from_string(source), context, ctx.app)