<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Hi Bruno,</div><div class=""><br class=""></div><div class="">thanks for the quick and helpful reply!</div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On 7 Dec 2016, at 22:23, Bruno Oliveira <<a href="mailto:nicoddemus@gmail.com" class="">nicoddemus@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="markdown-here-wrapper" style=""><p style="margin:1.2em 0px!important" class="">Hi Christoph,</p><p style="margin:1.2em 0px!important" class="">On Wed, Dec 7, 2016 at 11:51 AM Christoph Deil <a href="http://mailto:deil.christoph@googlemail.com/" class="">deil.christoph@googlemail.com</a> wrote:</p><div style="margin: 1.2em 0px !important;" class=""><br class="webkit-block-placeholder"></div><div class="markdown-here-exclude"><div class=""><br class="webkit-block-placeholder"></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg">Are there any real pros and cons for the two options? Or are both equally powerful and it’s a matter of taste?<br class=""></div></div></blockquote><div class=""><br class="webkit-block-placeholder"></div></div><div style="margin: 1.2em 0px !important;" class=""><br class="webkit-block-placeholder"></div><p style="margin:1.2em 0px!important" class="">IMHO it seems to be a matter of taste. The <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="">requires_dependency</code> function still requires you to explicitly import the module inside the test file to obtain the module object:</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px" class=""><code class="language-python hljs" style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important;display:block;overflow-x:auto;padding:0.5em;background:rgb(35,36,31);color:rgb(248,248,242)"><span class="hljs-keyword" style="color:rgb(249,38,114)">from</span> gammapy.utils.testing <span class="hljs-keyword" style="color:rgb(249,38,114)">import</span> requires_dependency
<span class="hljs-decorator" style="color:rgb(117,113,94)">@requires_dependency('scipy')</span>
<span class="hljs-function" style="color:rgb(249,38,114)"><span class="hljs-keyword" style="color:rgb(249,38,114);color:rgb(102,217,239)">def</span> <span class="hljs-title" style="color:rgb(166,226,46)">test_using_scipy</span><span class="hljs-params" style="color:rgb(248,248,242)">()</span>:</span>
<span class="hljs-keyword" style="color:rgb(249,38,114)">import</span> scipy
</code></pre><p style="margin:1.2em 0px!important" class="">Compared with <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="">pytest.importorskip</code>:</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px" class=""><code class="language-python hljs" style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important;display:block;overflow-x:auto;padding:0.5em;background:rgb(35,36,31);color:rgb(248,248,242)"><span class="hljs-keyword" style="color:rgb(249,38,114)">import</span> pytest
<span class="hljs-function" style="color:rgb(249,38,114)"><span class="hljs-keyword" style="color:rgb(249,38,114);color:rgb(102,217,239)">def</span> <span class="hljs-title" style="color:rgb(166,226,46)">test_using_scipy</span><span class="hljs-params" style="color:rgb(248,248,242)">()</span>:</span>
scipy = pytest.importorskip(<span class="hljs-string" style="color:rgb(230,219,116)">'scipy'</span>)
</code></pre><p style="margin:1.2em 0px!important" class="">So I think <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="">requires_dependency</code> has the following cons:</p>
<ul style="margin:1.2em 0px;padding-left:2em" class="">
<li style="margin:0.5em 0px" class="">It might be more explicit, since <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="">pytest.importorskip</code> might be used deep inside the test function and easy to miss, while the decorator stands out;</li>
<li style="margin:0.5em 0px" class="">It is more friendly to IDEs like PyCharm/PyDev, with code-completion, documentation, etc.</li>
</ul><p style="margin:1.2em 0px!important" class="">The only cons I can think of is that it requires one extra line and the extra import (since it is common for tests to import <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="">pytest</code> for other reasons as well).</p><div class=""><br class=""></div></div></div></div></blockquote><div><br class=""></div><div>Just to clarify: the way we handle optional dependencies in the (non-test) code is to put them as delayed imports only inside the function or method where they are used.</div><div><br class=""></div><div>E.g. we have classes that have much functionality for computation, and then one plot method and only that requires “import matplotlib”, because that import is in the plot method.</div><div><br class=""></div>So the extra “import scipy” line in the test code example you give above is never there in our tests.<br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="markdown-here-wrapper" style=""><div style="margin: 1.2em 0px !important;" class=""><br class="webkit-block-placeholder"></div><div class="markdown-here-exclude"><div class=""><br class="webkit-block-placeholder"></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg">Do you think such a decorator would be appropriate for a pytest plugin?<br class=""></div></div></blockquote><div class=""><br class="webkit-block-placeholder"></div></div><div style="margin: 1.2em 0px !important;" class=""><br class="webkit-block-placeholder"></div><p style="margin:1.2em 0px!important" class="">If others find it useful, I don’t see why not. :)</p><div style="margin: 1.2em 0px !important;" class=""><br class="webkit-block-placeholder"></div><div class="markdown-here-exclude"><div class=""><br class="webkit-block-placeholder"></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg"></div><div class="gmail_msg">Or even to be proposed as a convenience for pytest core?</div></div></blockquote><div class=""><br class="webkit-block-placeholder"></div></div><div style="margin: 1.2em 0px !important;" class=""><br class="webkit-block-placeholder"></div><p style="margin:1.2em 0px!important" class="">I personally would be -0 on this because I feel it seems too similar to using <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="">pytest.importorskip</code> method so I would avoid having two ways of doing the same thing. On the other hand, the implementation would be really simple so it wouldn’t be a maintenance burden if others really like it.</p><div class=""><br class=""></div></div></div></div></blockquote><div><br class=""></div><div>Makes sense.</div><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="markdown-here-wrapper" style=""><div style="margin: 1.2em 0px !important;" class=""><br class="webkit-block-placeholder"></div><div class="markdown-here-exclude"><div class=""><br class="webkit-block-placeholder"></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg">Or would you just recommend we implement what we want in our own `utils.py` instead of trying to generalise a solution for this?</div></div></blockquote><div class=""><br class="webkit-block-placeholder"></div></div><div style="margin: 1.2em 0px !important;" class=""><br class="webkit-block-placeholder"></div><p style="margin:1.2em 0px!important" class="">I think it is really commendable of you to try to provide a general solution to the community, so please don’t get discouraged by my <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="">-0</code>. And since the implementation is simple and <a href="https://github.com/pytest-dev/cookiecutter-pytest-plugin" class="">cookiecutter-pytest-plugin</a> makes creating plugins a snap, you should definitely go with it if you really prefer the decoration method.</p><div class=""><br class=""></div></div></div></div></blockquote><div><br class=""></div><div>I quickly looked through <a href="http://plugincompat.herokuapp.com/" class="">http://plugincompat.herokuapp.com/</a> and couldn’t find a plugin that does something like this, i.e. provide a decorator that can be used like this:</div><div>@requires_dependency(‘scipy”)</div><div>and maybe (to be discussed) a little more fancy strings and multiple checks like</div><div>@requires_dependency(‘scipy>=0.15, matplotlib’)</div><div><br class=""></div><div>I’ll check out the pytest cookiecutter.</div><div><br class=""></div><div>One basic question I still have is what the advantage is of having this as a Pytest plugin, instead of just a single-file .py module from which people can import the requires_dependency decorator? Would this allow me to expose the decorator in the top-level pytest or some other namespace? Is this a good idea?</div><div><br class=""></div><div><div>Are there one or a few examples of plugins that I could look at before getting started that are similar to what I’m trying to do?</div><div><br class=""></div><div>Cheers, Christoph</div><div class=""><br class=""></div></div></div><div><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="markdown-here-wrapper" style=""><p style="margin:1.2em 0px!important" class="">Cheers,<br class="">Bruno.</p>
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