<p dir="auto">The <a href="https://github.com/numpy/numpy/blob/master/doc/source/user/building.rst#prerequisites">build section of the user docs</a> says:</p>
<blockquote>
<p dir="auto">Compilers</p>
<p dir="auto">To build any extension modules for Python, you'll need a C compiler. Various NumPy modules use FORTRAN 77 libraries, so you'll also need a FORTRAN 77 compiler installed.</p>
</blockquote>
<p dir="auto">This is incorrect, and inconsistent with the <a href="https://github.com/numpy/numpy/blob/master/INSTALL.rst.txt#choosing-compilers">instructions in the main install file</a>, which state:</p>
<blockquote>
<p dir="auto">Fortran compiler isn't needed to build Numpy itself; the numpy.f2py tests will be skipped when running the test suite if no Fortran compiler is available. For building Scipy a Fortran compiler is needed though, so we include some details on Fortran compilers in the rest of this section.</p>
</blockquote>
<p dir="auto">The former is probably a remnant of the old scipy docs.</p>
<p dir="auto">I'm happy to submit a fix, but it would be good to know how folks want to deal with the duplication of those files.  As long as that information is carried in two duplicate locations, problems of divergence will keep reappearing.  Ideally there should be only one location to describe the source build process.</p>
<p dir="auto">The newest version of numpy raises an exception when being imported. I am using Python 3.9 64-bit on Windows 10.</p>
<h3 dir="auto">Reproducing code example:</h3>

<div class="highlight highlight-source-python notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="import numpy as np  # raises a RuntimeError"><pre class="notranslate"><span class="pl-k">import</span> <span class="pl-s1">numpy</span> <span class="pl-k">as</span> <span class="pl-s1">np</span>  <span class="pl-c"># raises a RuntimeError</span></pre></div>
<h3 dir="auto">Error message:</h3>


<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="$ python -c &quot;import numpy&quot;
 ** On entry to DGEBAL parameter number  3 had an illegal value
 ** On entry to DGEHRD  parameter number  2 had an illegal value
 ** On entry to DORGHR DORGQR parameter number  2 had an illegal value
 ** On entry to DHSEQR parameter number  4 had an illegal value
Traceback (most recent call last):
  File &quot;&lt;string&gt;&quot;, line 1, in &lt;module&gt;
  File &quot;C:\Users\Us\AppData\Roaming\Python\Python39\site-packages\numpy\__init__.py&quot;, line 305, in &lt;module&gt;
  _win_os_check()
  File &quot;C:\Users\Us\AppData\Roaming\Python\Python39\site-packages\numpy\__init__.py&quot;, line 302, in _win_os_check
  raise RuntimeError(msg.format(__file__))  from None
RuntimeError: The current Numpy installation ('C:\\Users\\Us\\AppData\\Roaming\\Python\\Python39\\site-packages\\numpy\\__init__.py') fails to pass a sanity check due to a bug in the windows runtime. See this issue for more information: https://lnkd.in/dg_VxHr"><pre class="notranslate"><code class="notranslate">$ python -c "import numpy"
 ** On entry to DGEBAL parameter number  3 had an illegal value
 ** On entry to DGEHRD  parameter number  2 had an illegal value
 ** On entry to DORGHR DORGQR parameter number  2 had an illegal value
 ** On entry to DHSEQR parameter number  4 had an illegal value
Traceback (most recent call last):
  File "&lt;string&gt;", line 1, in &lt;module&gt;
  File "C:\Users\Us\AppData\Roaming\Python\Python39\site-packages\numpy\__init__.py", line 305, in &lt;module&gt;
  _win_os_check()
  File "C:\Users\Us\AppData\Roaming\Python\Python39\site-packages\numpy\__init__.py", line 302, in _win_os_check
  raise RuntimeError(msg.format(__file__))  from None
RuntimeError: The current Numpy installation ('C:\\Users\\Us\\AppData\\Roaming\\Python\\Python39\\site-packages\\numpy\\__init__.py') fails to pass a sanity check due to a bug in the windows runtime. See this issue for more information: https://lnkd.in/dg_VxHr
</code></pre></div>
<h3 dir="auto">NumPy/Python version information:</h3>

<p dir="auto">NumPy 1.19.4<br>
Python 3.9.1<br>
<a target="_blank" rel="noopener noreferrer nofollow" href="https://user-images.githubusercontent.com/63655612/131376747-64859b5f-bc29-4a5a-9fce-950f662a8e3c.png"><img src="https://user-images.githubusercontent.com/63655612/131376747-64859b5f-bc29-4a5a-9fce-950f662a8e3c.png" alt="5b7544ad-bbfb-4ca3-886c-bc67e55ed5a9" style="max-width: 100%;"></a></p>