From f7cd942c36141fb711cbfb1ec631d43a42fcbaed Mon Sep 17 00:00:00 2001 From: DarkSun Date: Thu, 2 Apr 2020 01:02:23 +0800 Subject: [PATCH] =?UTF-8?q?=E9=80=89=E9=A2=98:=2020200401=203=20Python=20t?= =?UTF-8?q?emplating=20languages=20you=20should=20(probably)=20never=20use?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit sources/tech/20200401 3 Python templating languages you should (probably) never use.md --- ...nguages you should (probably) never use.md | 180 ++++++++++++++++++ 1 file changed, 180 insertions(+) create mode 100644 sources/tech/20200401 3 Python templating languages you should (probably) never use.md diff --git a/sources/tech/20200401 3 Python templating languages you should (probably) never use.md b/sources/tech/20200401 3 Python templating languages you should (probably) never use.md new file mode 100644 index 0000000000..e23b443b0d --- /dev/null +++ b/sources/tech/20200401 3 Python templating languages you should (probably) never use.md @@ -0,0 +1,180 @@ +[#]: collector: (lujun9972) +[#]: translator: ( ) +[#]: reviewer: ( ) +[#]: publisher: ( ) +[#]: url: ( ) +[#]: subject: (3 Python templating languages you should (probably) never use) +[#]: via: (https://opensource.com/article/20/4/python-templating-languages) +[#]: author: (Moshe Zadka https://opensource.com/users/moshez) + +3 Python templating languages you should (probably) never use +====== +Python has accumulated a lot of templating languages, including these +three that are perfect for April Fools' Day. +![Hands on a keyboard with a Python book ][1] + +When reaching for a templating language for writing a [Python][2] web application, there are an abundance of robust solutions.  + +There are [Jinja2][3], [Genshi, and Mako][4]. There are even solutions like [Chameleon][5], which are a bit older, but still recommended by the [Pyramid][6] framework. + +Python has been around for a long time. In that time, deep in the corners of its system, it has accumulated some almost forgotten templating languages that are well worth poking at. + +Like cute koalas on top of a eucalyptus tree, happy in their ecological niche, and sometimes as dangerous to work with, these are the templating languages few have heard of—and even fewer should use. + +### 3\. string.Template + +Have you ever wondered, "How can I get a templating language with no features, but also without needing to **pip install** anything?" The Python standard library has you covered. While it does no looping or conditionals, the **string.Template** class is a minimal templating language. + +Using it is simplicity itself. + + +``` +>>> import string +>>> greeting = string.Template("Hello, $name, good $time!") +>>> greeting.substitute(name="OpenSource.com", time="afternoon") +'Hello, OpenSource.com, good afternoon!' +``` + +### 2\. twisted.web.template + +What gift do you give the library that has everything? + +Not a templating language, certainly, because it already has one. Nestled in **twisted.web.template** are two templating languages. One is XML-based and has a [great tutorial][7]. + +But there is another one, one that is based on using Python as a domain-specific language to produce HTML documents. + +It is based on two primitives: **twisted.web.template.tags**, which contains tag objects, and **twisted.web.template.flattenString**, which will render them. Because it is part of Twisted, it has built-in support for rendering async results efficiently. + +This example will render a silly little page: + + +``` +async def render(reactor): +    my_title = "A Fun page" +    things = ["one", "two", "red", "blue"] +    template = tags.html( +            tags.head( +                tags.title(my_title), +            ), +            tags.body( +                tags.h1(my_title), +                tags.ul( +                    [tags.li(thing) for thing in things], +                ), +                tags.p( +                    task.deferLater(reactor, 3, lambda: "Hello "), +                    task.deferLater(reactor, 3, lambda: "world!"), +                ) +            ) +    ) +    res = await flattenString(None, template) +    res = res.decode('utf-8') +    with open("hello.html", 'w') as fpout: +        fpout.write(res) +``` + +The template is regular Python code that uses the **tags.<TAGNAME>** to indicate the hierarchy. It natively supports strings as renderables, so any string is fine. + +To render it, the only things you need to do are to add a preamble: + + +``` +from twisted.internet import task, defer +from twisted.web.template import tags, flattenString + +def main(reactor): +    return defer.ensureDeferred(render(reactor)) +``` + +and an epilogue to run the whole thing: + + +``` +`task.react(main)` +``` + +In just _three_ seconds (and not _six_), it will render a nice HTML page. In real-life, those **deferLater**s can be, for example, calls to an HTTP API: they will be sent and processed in parallel, without having to put in any effort. I recommend you instead read about a [far better use for Twisted][8]. But still, this works. + +### 1\. Quixote + +You will say, "But Python is not _optimized_ for being an HTML-spouting domain-specific language." What if, instead of settling for Python-as-is, there was a language that [transpiles][9] to Python, but is better at defining templates? A "Python template language" (PTL), if you will. + +Writing your own language is sometimes said to be a dreamer's project for someone who tilts at windmills. Irony was not lost on the creators of Quixote (available on [PyPI][10]) when they decided to do exactly that. + +The following will render an equivalent template to the one done with Twisted above. _Warning: the following is not valid Python_: + + +``` +import time + +def render [html] (): +    my_title = "A Fun page" +    things = ["one", "two", "red", "blue"] +    "<html><head><title>" +    my_title +    "</head></title><body><h1>" +    my_title +    "</h1>" +    "<ul>" +    for thing in things: +        "<li>" +        thing +        "</li>" +    "<p>" +    time.sleep(3) +    (lambda: "Hello ")() +    time.sleep(3) +    (lambda: "world!")() +    "</p>" +    "</body></html>" + +def write(): +    result = render() +    with open("hello.html", 'w') as fpout: +        fpout.write(str(result)) +``` + +However, if you put it in a file called **template.ptl**, you can make it importable to Quixote and write out the rendered version of the template: + + +``` +>>> from quixote import enable_ptl +>>> enable_ptl() +>>> import template +>>> template.write() +``` + +Quixote installs an import hook that will cause PTL files to transpile into Python. Note that this render takes _six_ seconds, not _three_; you no longer gain free asynchronicity. + +### So many templates in Python + +Python has a long and winding history of libraries, some of which can achieve the same outcomes in more or less similar ways (for example, Python [package management][11]). + +On this April Fools' Day, I hope you enjoyed exploring three ways you _can_ create templates in Python. Instead, I recommend starting with [one of these libraries][4] for ways you _should_ template. + +Do you have another esoteric way to template? Share it in the comments below! + +-------------------------------------------------------------------------------- + +via: https://opensource.com/article/20/4/python-templating-languages + +作者：[Moshe Zadka][a] +选题：[lujun9972][b] +译者：[译者ID](https://github.com/译者ID) +校对：[校对者ID](https://github.com/校对者ID) + +本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出 + +[a]: https://opensource.com/users/moshez +[b]: https://github.com/lujun9972 +[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/python-programming-code-keyboard.png?itok=fxiSpmnd (Hands on a keyboard with a Python book ) +[2]: https://opensource.com/resources/python +[3]: https://opensource.com/article/20/2/jinja2-cheat-sheet +[4]: https://opensource.com/resources/python/template-libraries +[5]: https://chameleon.readthedocs.io/en/latest/ +[6]: https://opensource.com/article/18/5/pyramid-framework +[7]: https://twistedmatrix.com/documents/13.1.0/web/howto/twisted-templates.html +[8]: https://opensource.com/article/20/3/treq-python +[9]: https://en.wikipedia.org/wiki/Source-to-source_compiler +[10]: https://pypi.org/project/Quixote/ +[11]: https://opensource.com/article/19/4/managing-python-packages