{"id":366,"date":"2020-12-05T10:12:50","date_gmt":"2020-12-05T15:12:50","guid":{"rendered":"https:\/\/www.alpharithms.com\/?p=366"},"modified":"2022-06-16T15:24:11","modified_gmt":"2022-06-16T19:24:11","slug":"noqa-python","status":"publish","type":"post","link":"https:\/\/www.alpharithms.com\/noqa-python-501210\/","title":{"rendered":"NOQA: Simple PEP8 Warning Suppression"},"content":{"rendered":"<p>No Quality Assurance (# noqa) is a computer programming directive by which a programmer can instruct errors to be ignored for a given line. The NOQA syntax is used in the Python programming language to instruct code inspection tools such as <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">pycodestyle<\/code>, <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">pyflakes<\/code>, and <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">mccabe<\/code> to ignore errors can be directed to ignore specific errors.<\/p>\n<p>The <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> syntax was originally used as <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># nopep8<\/code> to indicate that Flake should skip pep8 warnings for a particular line. Evolution to accommodate ignoring other, non-style-based warnings, lead to the more general <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> syntax. Simply put; the <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> directive means <em>Don&#8217;t worry about errors generated by this line of code.<\/em><\/p>\n<h2>History &amp; Evolution<\/h2>\n<p>The <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> directive lends itself to several use-cases including broad directives, specific error codes, and even multiple error codes. From the <a href=\"https:\/\/pypi.org\/project\/flake8\/\">Flake8 documentation<\/a>:<\/p>\n<p><em>files that contain this line are skipped<\/em>:<\/p>\n<ul>\n<li><code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># flake8: noqa<\/code><\/li>\n<li>Lines that contain a <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> comment at the end will not issue warnings.<\/li>\n<li>You can ignore specific errors on a line with <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa: &lt;error&gt;<\/code>, e.g., <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa: E234<\/code>.<\/li>\n<li>Multiple codes can be given, separated by a comma. The <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">noqa<\/code> token is case insensitive, the colon before the list of codes is required otherwise the part after <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">noqa<\/code> is ignored<\/li>\n<\/ul>\n<h2>Examples<\/h2>\n<p>Given its history, it seems fitting to illustrate Flake8 usage of the <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> directive. To get started, simply install the package as such:<\/p>\n<p><code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">$ pip install flake8<\/code><\/p>\n<p>Watching the console output during installation, you might note the following dependencies being installed:<\/p>\n<p><code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">Succesfully installed flake8-x.x.x mccabe-x.x.x pycodestyle-x.x.x pyflakes-x.x.x<\/code><\/p>\n<p>After which flake can be run against any module or directory when specified as an argument like this:<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">$ flake project\r\n\r\n$ flake project\/module\r\n\r\n$ flake project\/module\/submodule<\/pre>\n<p>Let&#8217;s now consider an example of poorly-written\u00a0 Python code such that Flake8 might be used to generate some warnings. The following code contains 8 errors, can you spot them?<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">import os\r\n\r\n\r\ndef foo():\r\n    pass\r\n    \r\ndef foo():\r\n    pass\r\n    \r\nx=5\r\n\r\nprint(\"46 equals 2 = \", 46 == 2)<\/pre>\n<p>In this very contrived example, there are some immediately obvious issues. For one, the foo function is defined twice. The others are more subtle however and might not jump out immediately. That&#8217;s where code inspection tools come in handy. By running the <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">$ flake8 file.py<\/code> command the following output is produced:<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">file.py:1:1: F401 'os' imported but unused\r\nfile.py:6:1: W293 blank line contains whitespace\r\nfile.py:7:1: E302 expected 2 blank lines, found 1\r\nfile.py:7:1: F811 redefinition of unused 'foo' from line 4\r\nfile.py:9:1: W293 blank line contains whitespace\r\nfile.py:10:1: E305 expected 2 blank lines after class or function definition, found 1\r\nfile.py:10:2: E225 missing whitespace around operator\r\nfile.py:12:33: W292 no newline at end of file<\/pre>\n<p>To illustrate the usage of the <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> operator, consider the code from above again\u2014but this time with general and specific <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> declarations:<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">import os   # noqa: F401 used for comfort only\r\n\r\n\r\ndef foo():\r\n    pass\r\n    \r\ndef foo():  # noqa\r\n    pass\r\n    \r\nx=5 # noqa: E225\r\n\r\nprint(\"46 equals 2 = \", 46 == 2)<\/pre>\n<p>In this example, three unique <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> directives have been declared. The new output when running the <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">$ flake8 new_file.py<\/code> command is as follows:<\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">newfile.py:6:1: W293 blank line contains whitespace\r\nnewfile.py:9:1: W293 blank line contains whitespace\r\nnewfile.py:10:1: E305 expected 2 blank lines after class or function definition, found 1\r\nnewfile.py:10:4: E261 at least two spaces before inline comment\r\nnewfile.py:12:33: W292 no newline at end of file<\/pre>\n<p>The <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> directive removed warnings for the lines in which it was included! In this\u00a0<em>extremely<\/em> contrived example, it&#8217;s difficult to imagine practical uses of such directives. However, flake (and other common code inspection tools) can be useful in the followings cases:<\/p>\n<ol>\n<li>Including a module\u00a0<em>just<\/em> for the purposes of documentation<\/li>\n<li>Ignoring line-formatting for the construction of strings<\/li>\n<li>Ignoring line-length errors if preferred (not recommended)<\/li>\n<li>Project-required actions before module-level imports<\/li>\n<li>Other crazy sh*t that only your project requires<\/li>\n<\/ol>\n<p>Flake8 also supports pre-commit hooking to ensure that all code has been inspected prior to version control commits. See <a href=\"https:\/\/flake8.pycqa.org\/en\/latest\/user\/using-hooks.html\">more here<\/a>.<\/p>\n<p style=\"text-align: center;\"><em>The examples from this article are <a href=\"https:\/\/github.com\/theovercoded\/examples\/tree\/main\/python\/flake_examples\">available on GitHub<\/a>.<\/em><\/p>\n<h2>IDE Support<\/h2>\n<p>Flake8, Pylint, and similar tools aren&#8217;t always accommodated by popular IDEs such as IntelliJ and VisualStudio. However, the popularity of these tools has directed the development of IDE-specific code-inspection tools that share many of the same features.<\/p>\n<p>For example, Jetbrains&#8217; PyCharm contains a <a href=\"https:\/\/www.jetbrains.com\/help\/pycharm\/disabling-and-enabling-inspections.html#suppress-inspections\">code-inspection toolset<\/a> that allows for use of the <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\"># noqa<\/code> syntax alongside their more novel syntax systems. You can use the # noqa directive to specify both <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">flake8<\/code> and <code class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\">pycodestyle<\/code> error codes. In addition, Many IDEs like PyCharm allow configuration within their own settings frameworks to limit warning levels, warning types, and even the presentation of warnings.<\/p>\n<h2>Discussion<\/h2>\n<p>Code inspection tools are useful in helping to ensure efficiency and interoperability. Just because\u00a0<em>you<\/em> know how something works doesn&#8217;t mean the next developer will be able to discern such. Ensuring code conforms\u2014as closely as is practically allowable\u2014to common convention helps harbor interoperability.<\/p>\n<p>The #noqa directive is particularly useful in informing code inspectors to\u00a0<em>ignore<\/em> specific lines. This allows developers to do things that might not make sense to a code inspector, but make sense for the project. The flake8 module will provide access to these tools as will most modern IDEs like PyCharm.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>No Quality Assurance (# noqa) is a computer programming directive by which a programmer can instruct errors to be ignored for a given line. The NOQA syntax is used in the Python programming language to instruct code inspection tools such as pycodestyle, pyflakes, and mccabe to ignore errors can be directed to ignore specific errors. [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":365,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[655,10],"tags":[181,176,182,179,180,177,178],"acf":[],"_links":{"self":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/366"}],"collection":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/comments?post=366"}],"version-history":[{"count":1,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/366\/revisions"}],"predecessor-version":[{"id":367,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/366\/revisions\/367"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/media\/365"}],"wp:attachment":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/media?parent=366"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/categories?post=366"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/tags?post=366"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}