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1 <!DOCTYPE html>
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2 <html>
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3 <head>
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4 <meta http-equiv="content-type" content="text/html; charset=UTF-8">
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5 <title>Introducing TinCan</title>
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6 <style type="text/css">
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7 .kbd { font-family: monospace; }
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8 </style>
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9 </head>
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10 <body>
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11 <h1>Introducing TinCan, a “Code-Behind” MVC Framework for Bottle</h1>
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12 <h2>Introduction</h2>
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13 <p>TinCan is a Python 3 code-behind web framework implemented in the Bottle
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14 microframework. As with Bottle, all the code is in one module, and there
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15 is no direct dependency on anything that is not part of the standard
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16 Python library (except of course for Bottle itself).</p>
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17 <p>The default templating engine for TinCan is <a href="https://chameleon.readthedocs.io/en/latest/">Chameleon</a>.
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18 TinCan adds Chameleon as a fully-supported templating engine for Bottle.
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19 Any template engine supported by Bottle can be used to render TinCan
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20 Pages.</p>
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21 <h2>Why Do This?</h2>
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22 <p>In short, there is too much repeating oneself in most all Python web
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23 frameworks (and this includes Bottle). One is always saying “this is
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24 controller <span class="kbd">foo</span>, whose view is in the template <span
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25 class="kbd">foo.pt</span>, at route <span class="kbd">/foo</span>.”</p>
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26 <p>That’s a lot more busywork than just writing <span class="kbd">foo.php</span>
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27 or <span class="kbd">foo.cgi</span>, so many simple webapps end up being
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28 implemented via the latter means. That’s unfortunate, as CGI isn’t very
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29 resource-efficient, and there’s much nicer languages to code in than PHP
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30 (such as Python :-) ). Worst of all, you now have logic and presentation
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31 all scrambled together, never a good idea.</p>
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32 <p>What if, instead, you could write <span class="kbd">foo.pspx</span> and
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33 <span class="kbd">foo.py</span>, and a framework would automatically
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34 create the <span class="kbd">/foo.pspx</span> route for you, much like
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35 ASP.NET or JSP would for a <span class="kbd">.aspx</span> or <span class="kbd">.jsp</span>
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36 file? The matching code-behind in the <span class="kbd">.py</span> file
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37 would be easily detected (same name, different extension) and
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38 automatically associated with the template, of course. You could focus on
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39 writing pages instead of repeating yourself saying the obvious over and
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40 over again. </p>
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41 <p>This is what TinCan lets you do.</p>
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42 <h2>Hang On, Code-Behind Isn’t MVC!</h2>
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43 <p>Why <em>isn’t</em> it? The model, as always, is the data and containing
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44 core business logic. The template file defines the view presented to the
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45 user, and the code-behind is the intermediary between the two. A
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46 controller by any other name…</p>
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47 <h2>How Can There Be Multiple Views for One Controller?</h2>
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48 <p>Easily. Take a look at the <code>#python</code> header directive. </p>
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49 <h2>Multiple Controllers for One View?</h2>
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50 <p>Personally, I don’t think this is the best of ideas. Just because two
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51 controllers might be able to share a view <em>now</em> does not mean they
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52 will continue to in the future. Then you change one (controller, view)
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53 pair and another controller someplace else breaks!</p>
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54 <p>However, if you insist, check out the <code>#template</code> and <code>#hidden</code>
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55 header directives. </p>
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56 <h2>But This Causes Less SEO-Friendly Routes!</h2>
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57 <p>First, this is not always important. Sometimes, all you want to do is get
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58 a small, simple, special-purpose, site up and running with a minimum of
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59 busywork. Why should you be forced to do more work just because that extra
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60 work benefits someone <em>else</em>?</p>
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61 <p>Second, when it is, you can always use <code>RewriteRule</code> (Apache)
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62 <code>rewrite</code> (nginx), or the equivalent in your favorite Web
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63 server, and code your templates to use the SEO-friendly version of your
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64 URL’s. With TinCan sitting behind a good, production-grade web server, you
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65 get the best of both worlds: fast, simple deployment when you want it, and
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66 SEO-friendly URL’s when you want it. </p>
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67 <h2>But What about Routing Things Based on Both Path and Method?</h2>
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68 <p>That’s easy enough to do, as TinCan is implemented on top of Bottle. You
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69 can add your Bottle routes, using the <code>@route</code> decorator on
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70 your controller methods, same as always. Just stick them in the same
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71 start-up script you use to launch your TinCan files.</p>
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72 <p>If for some reason you don’t want to mess with manually creating routes
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73 and associating them with controllers in Bottle (even in cases like this
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74 where it arguably makes sense), and want to do <em>everything</em> the
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75 TinCan way, you can create a set of hidden (using the <code>#hidden</code>
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76 directive) pages and a main dummy page whose code-behind forwards (<code>page.request.app.forward</code>)
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77 to the appropriate hidden page depending on request method. </p>
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78 <h2>What about Launching Multiple TinCan Webapps?</h2>
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79 <p>It works just as well (and just as poorly) as launching multiple Bottle
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80 webapps. Note that the big limitation here is Python’s module subsystem;
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81 there is only one. Thus, all webapps share the same module path. There is
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82 no way to have one webapp using an older version of a given module served
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83 by the same server as another using a newer version, save renaming one of
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84 the modules. This is a Python issue, not a Bottle issue or a TinCan issue.</p>
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85 <p>Note that TinCan bypasses the Python module cache and manages its own
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86 importing of code-behind files, so there is no problem if you have
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87 multiple webapps using the same relative URL paths. TinCan will keep all
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88 those code-behind files straight; it will not confuse one webapp’s <span
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89 class="kbd">/index.py</span> with another’s.</p>
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90 <h2>What about Bottle Plugins?</h2>
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91 <p>I am working on adding support for these.</p>
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92 </body>
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93 </html>
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