Tornado框架模板引擎本质
只需要了解一下即可
本篇就来详细的剖析模板处理的整个过程。
上图是返回给用户一个html文件的整个流程，较之前的Demo多了绿色流线的步骤，其实就是把【self.write('hello world')】变成了【self.render('main.html')】，对于所有的绿色流线只做了五件事：
- 使用内置的open函数读取Html文件中的内容
- 根据模板语言的标签分割Html文件的内容，例如：{{}} 或 {%%}
- 将分割后的部分数据块格式化成特殊的字符串（表达式）
- 通过python的内置函数执行字符串表达式，即：将html文件的内容和嵌套的数据整合
- 将数据返回给请求客户端
所以，如果要返回给客户端对于一个html文件来说，根据上述的5个阶段其内容的变化过程应该是这样：
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.render("main.html",**{'data':['11','22','33'],'title':'main'})
[main.html]
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
</head>
<body>
<h1>{{title}}</h1>
{% for item in data %}
<h3>{{item}}</h3>
{% end %}
</body>
</html>
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
</head>
<body>
<h1>{{title}}</h1>
{% for item in data %}
<h3>{{item}}</h3>
{% end %}
</body>
</html>
第1块：'<!DOCTYPE html><html><head lang="en"><meta charset="UTF-8"><title></title></head><h1>'
第2块：'title'
第3块：'</h1>
'
第4块：'for item in data'
第4.1块：'
<h3>'
第4.2块：'item'
第4.3块：'</h3>
'
第五块：'</body>'
'def _execute():
_buffer = []
_buffer.append(\'<!DOCTYPE html>\n<html>\n<head lang="en">\n<meta charset="UTF-8">\n<title></title>\n</head>\n<body>\n<h1>\')
_tmp = title
if isinstance(_tmp, str): _buffer.append(_tmp)
elif isinstance(_tmp, unicode): _buffer.append(_tmp.encode(\'utf-8\'))
else: _buffer.append(str(_tmp))
_buffer.append(\'</h1>\n\')
for item in data:
_buffer.append(\'\n<h3>\')
_tmp = item
if isinstance(_tmp, str): _buffer.append(_tmp)
elif isinstance(_tmp, unicode): _buffer.append(_tmp.encode(\'utf-8\'))
else: _buffer.append(str(_tmp))
_buffer.append(\'</h3>\n\')
_buffer.append(\'\n</body>\n</html>\')
return \'\'.join(_buffer)
'
RequestHandler的render方法
此段代码主要有三项任务：
- 获取Html文件内容并把数据（程序数据或框架自带数据）嵌套在内容中的指定标签中（本篇主题）
- 执行ui_modules，再次在html中插入内容，例：head，js文件、js内容、css文件、css内容和body
- 内部调用客户端socket，将处理请求后的数据返回给请求客户端
-
class RequestHandler(object): def render(self, template_name, **kwargs): #根据Html文件名称获取文件内容并把参数kwargs嵌入到内容的指定标签内 html = self.render_string(template_name, **kwargs) #执行ui_modules，再在html的内容中插入head，js文件、js内容、css文件、css内容和body信息。 js_embed = [] js_files = [] css_embed = [] css_files = [] html_heads = [] html_bodies = [] for module in getattr(self, "_active_modules", {}).itervalues(): embed_part = module.embedded_javascript() if embed_part: js_embed.append(_utf8(embed_part)) file_part = module.javascript_files() if file_part: if isinstance(file_part, basestring): js_files.append(file_part) else: js_files.extend(file_part) embed_part = module.embedded_css() if embed_part: css_embed.append(_utf8(embed_part)) file_part = module.css_files() if file_part: if isinstance(file_part, basestring): css_files.append(file_part) else: css_files.extend(file_part) head_part = module.html_head() if head_part: html_heads.append(_utf8(head_part)) body_part = module.html_body() if body_part: html_bodies.append(_utf8(body_part)) if js_files:#添加js文件 # Maintain order of JavaScript files given by modules paths = [] unique_paths = set() for path in js_files: if not path.startswith("/") and not path.startswith("http:"): path = self.static_url(path) if path not in unique_paths: paths.append(path) unique_paths.add(path) js = ''.join('<script src="' + escape.xhtml_escape(p) + '" type="text/javascript"></script>' for p in paths) sloc = html.rindex('</body>') html = html[:sloc] + js + ' ' + html[sloc:] if js_embed:#添加js内容 js = '<script type="text/javascript"> //<![CDATA[ ' + ' '.join(js_embed) + ' //]]> </script>' sloc = html.rindex('</body>') html = html[:sloc] + js + ' ' + html[sloc:] if css_files:#添加css文件 paths = [] unique_paths = set() for path in css_files: if not path.startswith("/") and not path.startswith("http:"): path = self.static_url(path) if path not in unique_paths: paths.append(path) unique_paths.add(path) css = ''.join('<link href="' + escape.xhtml_escape(p) + '" ' 'type="text/css" rel="stylesheet"/>' for p in paths) hloc = html.index('</head>') html = html[:hloc] + css + ' ' + html[hloc:] if css_embed:#添加css内容 css = '<style type="text/css"> ' + ' '.join(css_embed) + ' </style>' hloc = html.index('</head>') html = html[:hloc] + css + ' ' + html[hloc:] if html_heads:#添加html的header hloc = html.index('</head>') html = html[:hloc] + ''.join(html_heads) + ' ' + html[hloc:] if html_bodies:#添加html的body hloc = html.index('</body>') html = html[:hloc] + ''.join(html_bodies) + ' ' + html[hloc:] #把处理后的信息响应给客户端 self.finish(html)
对于上述三项任务，第一项是模板语言的重中之重，读取html文件并将数据嵌套到指定标签中，以下的步骤用于剖析整个过程（详情见下文）；第二项是对返会给用户内容的补充，也就是在第一项处理完成之后，利用ui_modules再次在html中插入内容（head，js文件、js内容、css文件、css内容和body）；第三项是通过socket将内容响应给客户端（见上篇）。
对于ui_modules，每一个ui_module其实就是一个类，一旦注册并激活了该ui_module，tornado便会自动执行其中的方法：embedded_javascript、javascript_files、embedded_css、css_files、html_head、html_body和render ，从而实现对html内容的补充。（执行过程见上述代码）
自定义UI Modules
此处是一个完整的 创建 --> 注册 --> 激活 的Demo
目录结构：
├── index.py
├── static
└── views
└── index.html
#!/usr/bin/env python
# -*- coding:utf-8 -*-
import tornado.ioloop
import tornado.web
class CustomModule(tornado.web.UIModule):
def embedded_javascript(self):
return 'embedded_javascript'
def javascript_files(self):
return 'javascript_files'
def embedded_css(self):
return 'embedded_css'
def css_files(self):
return 'css_files'
def html_head(self):
return 'html_head'
def html_body(self):
return 'html_body'
def render(self):
return 'render'
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.render('index.html')
settings = {
'static_path': 'static',
"template_path": 'views',
"ui_modules": {'Foo': CustomModule},
}
application = tornado.web.Application([(r"/", MainHandler), ], **settings)
if __name__ == "__main__":
application.listen(8888)
tornado.ioloop.IOLoop.instance().start()
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
</head>
<body>
<hr>
{% module Foo() %}
<hr>
</body>
</html>
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
<!-- css_files -->
<link href="/static/css_files" type="text/css" rel="stylesheet">
<!-- embedded_css -->
<style type="text/css">
embedded_css
</style>
</head>
<body>
<!-- html_head -->
html_head
<hr>
<!-- redner -->
render
<hr>
<!-- javascript_files -->
<script src="/static/javascript_files" type="text/javascript"></script>
<!-- embedded_javascript -->
<script type="text/javascript">
//<![CDATA[
embedded_javascript
//]]>
</script>
<!-- html_body -->
html_body
</body>
</html>
RequestHandler的render_string方法
该方法是本篇的重中之重，它负责去处理Html模板并返回最终结果，【概述】中提到的5件事中前四件都是此方法来完成的，即：
- 创建Loader对象，并执行load方法
-- 通过open函数打开html文件并读取内容，并将内容作为参数又创建一个 Template 对象
-- 当执行Template的 __init__ 方法时，根据模板语言的标签 {{}}、{%%}等分割并html文件，最后生成一个字符串表示的函数 - 获取所有要嵌入到html模板中的变量，包括：用户返回和框架默认
- 执行Template对象的generate方法
-- 编译字符串表示的函数，并将用户定义的值和框架默认的值作为全局变量
-- 执行被编译的函数获取被嵌套了数据的内容，然后将内容返回（用于响应给请求客户端）
class RequestHandler(object): def render_string(self, template_name, **kwargs): #获取配置文件中指定的模板文件夹路径，即：template_path ＝ 'views' template_path = self.get_template_path() #如果没有配置模板文件的路径，则默认去启动程序所在的目录去找 if not template_path: frame = sys._getframe(0) web_file = frame.f_code.co_filename while frame.f_code.co_filename == web_file: frame = frame.f_back template_path = os.path.dirname(frame.f_code.co_filename) if not getattr(RequestHandler, "_templates", None): RequestHandler._templates = {} #创建Loader对象，第一次创建后，会将该值保存在RequestHandler的静态字段_template_loaders中 if template_path not in RequestHandler._templates: loader = self.application.settings.get("template_loader") or template.Loader(template_path) RequestHandler._templates[template_path] = loader #执行Loader对象的load方法，该方法内部执行执行Loader的_create_template方法 #在_create_template方法内部使用open方法会打开html文件并读取html的内容，然后将其作为参数来创建一个Template对象 #Template的构造方法被执行时，内部解析html文件的内容，并根据内部的 {{}} {%%}标签对内容进行分割，最后生成一个字符串类表示的函数并保存在self.code字段中 t = RequestHandler._templates[template_path].load(template_name) #获取所有要嵌入到html中的值和框架默认提供的值 args = dict( handler=self, request=self.request, current_user=self.current_user, locale=self.locale, _=self.locale.translate, static_url=self.static_url, xsrf_form_html=self.xsrf_form_html, reverse_url=self.application.reverse_url ) args.update(self.ui) args.update(kwargs) #执行Template的generate方法，编译字符串表示的函数并将namespace中的所有key，value设置成全局变量，然后执行该函数。从而将值嵌套进html并返回。 return t.generate(**args)
class Loader(object):
"""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):
self.root = os.path.abspath(root_directory)
self.templates = {}
class Loader(object):
def load(self, name, parent_path=None):
name = self.resolve_path(name, parent_path=parent_path)
if name not in self.templates:
path = os.path.join(self.root, name)
f = open(path, "r")
#读取html文件的内容
#创建Template对象
#name是文件名
self.templates[name] = Template(f.read(), name=name, loader=self)
f.close()
return self.templates[name]
class Template(object):
def __init__(self, template_string, name="<string>", loader=None,compress_whitespace=None):
# template_string是Html文件的内容
self.name = name
if compress_whitespace is None:
compress_whitespace = name.endswith(".html") or name.endswith(".js")
#将内容封装到_TemplateReader对象中，用于之后根据模板语言的标签分割html文件
reader = _TemplateReader(name, template_string)
#分割html文件成为一个一个的对象
#执行_parse方法，将html文件分割成_ChunkList对象
self.file = _File(_parse(reader))
#将html内容格式化成字符串表示的函数
self.code = self._generate_python(loader, compress_whitespace)
try:
#将字符串表示的函数编译成函数
self.compiled = compile(self.code, self.name, "exec")
except:
formatted_code = _format_code(self.code).rstrip()
logging.error("%s code:
%s", self.name, formatted_code)
raise
class Template(object):
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,
}
#创建变量环境并执行函数，详细Demo见上一篇博文
namespace.update(kwargs)
exec self.compiled in namespace
execute = namespace["_execute"]
try:
#执行编译好的字符串格式的函数，获取嵌套了值的html文件
return execute()
except:
formatted_code = _format_code(self.code).rstrip()
logging.error("%s code:
%s", self.name, formatted_code)
raise
其中涉及的类有：
class _TemplateReader(object):
def __init__(self, name, text):
self.name = name
self.text = text
self.line = 0
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("
", 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:]
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
def _parse(reader, in_block=None):
#默认创建一个内容为空列表的_ChunkList对象
body = _ChunkList([])
# 将html块添加到 body.chunks 列表中
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()))
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:
body.chunks.append(_Text(reader.consume(curly)))
start_brace = reader.consume(2)
line = reader.line
# Expression
if start_brace == "{{":
end = reader.find("}}")
if end == -1 or reader.find("
", 0, 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))
continue
# Block
assert start_brace == "{%", start_brace
end = reader.find("%}")
if end == -1 or reader.find("
", 0, 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"]),
"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))
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"):
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)
elif operator == "include":
suffix = suffix.strip('"').strip("'")
if not suffix:
raise ParseError("include missing file path on line %d" % line)
block = _IncludeBlock(suffix, reader)
elif operator == "set":
if not suffix:
raise ParseError("set missing statement on line %d" % line)
block = _Statement(suffix)
body.chunks.append(block)
continue
elif operator in ("apply", "block", "try", "if", "for", "while"):
# parse inner body recursively
block_body = _parse(reader, operator)
if operator == "apply":
if not suffix:
raise ParseError("apply missing method name on line %d" % line)
block = _ApplyBlock(suffix, block_body)
elif operator == "block":
if not suffix:
raise ParseError("block missing name on line %d" % line)
block = _NamedBlock(suffix, block_body)
else:
block = _ControlBlock(contents, block_body)
body.chunks.append(block)
continue
else:
raise ParseError("unknown operator: %r" % operator)
class Template(object):
def _generate_python(self, loader, compress_whitespace):
buffer = cStringIO.StringIO()
try:
named_blocks = {}
ancestors = self._get_ancestors(loader)
ancestors.reverse()
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, self,
compress_whitespace)
ancestors[0].generate(writer)
return buffer.getvalue()
finally:
buffer.close()
so，上述整个过程其实就是将一个html转换成一个函数，并为该函数提供全局变量，然后执行该函数！！
结束语
上述就是对于模板语言的整个流程，其本质就是处理html文件内容将html文件内容转换成函数，然后为该函数提供全局变量环境（即：我们想要嵌套进html中的值和框架自带的值），再之后执行该函数从而获取到处理后的结果，再再之后则执行UI_Modules继续丰富返回结果，例如：添加js文件、添加js内容块、添加css文件、添加css内容块、在body内容第一行插入数据、在body内容最后一样插入数据，最终，通过soekct客户端对象将处理之后的返回结果（字符串）响应给请求用户。