title: matplotlib doesn't save graph as file on raspberrypi
body: <p>I have a question about the matplotlib on raspberry pi
  I have following code:</p>
  <pre><code>import matplotlib.pyplot as plt
  
  data = [100, 200, 500, 700, 300, 200, 500]
  x =[1, 2, 3, 4, 5, 6, 7]
  
  plt.plot(x, data, color='w')
  plt.xlabel('x axis')
  plt.ylabel('y axis')
  plt.savefig(&quot;test.png&quot;)
  </code></pre>
  <p>The code works perfectly fine on my computer but on the raspberry pi I get following Error:</p>
  <pre><code>Traceback (most recent call last):
    File &quot;/home/pi/.local/lib/python3.7/site-packages/numpy/core/__init__.py&quot;, line 22, in &lt;module&gt;
      from . import multiarray
    File &quot;/home/pi/.local/lib/python3.7/site-packages/numpy/core/multiarray.py&quot;, line 12, in &lt;module&gt;
      from . import overrides
    File &quot;/home/pi/.local/lib/python3.7/site-packages/numpy/core/overrides.py&quot;, line 7, in &lt;module&gt;
      from numpy.core._multiarray_umath import (
  ImportError: /lib/arm-linux-gnueabihf/libm.so.6: version `GLIBC_2.27' not found (required by /home/pi/.local/lib/python3.7/site-packages/numpy/core/_multiarray_umath.cpython-37m-arm-linux-gnueabihf.so)
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File &quot;test.py&quot;, line 1, in &lt;module&gt;
      import matplotlib.pyplot as plt
    File &quot;/home/pi/.local/lib/python3.7/site-packages/matplotlib/__init__.py&quot;, line 107, in &lt;module&gt;
      from . import cbook, rcsetup
    File &quot;/home/pi/.local/lib/python3.7/site-packages/matplotlib/cbook/__init__.py&quot;, line 28, in &lt;module&gt;
      import numpy as np
    File &quot;/home/pi/.local/lib/python3.7/site-packages/numpy/__init__.py&quot;, line 140, in &lt;module&gt;
      from . import core
    File &quot;/home/pi/.local/lib/python3.7/site-packages/numpy/core/__init__.py&quot;, line 48, in &lt;module&gt;
      raise ImportError(msg)
  ImportError:
  
  IMPORTANT: PLEASE READ THIS FOR ADVICE ON HOW TO SOLVE THIS ISSUE!
  
  Importing the numpy C-extensions failed. This error can happen for
  many reasons, often due to issues with your setup or how NumPy was
  installed.
  
  We have compiled some common reasons and troubleshooting tips at:
  
      https://numpy.org/devdocs/user/troubleshooting-importerror.html
  
  Please note and check the following:
  
    * The Python version is: Python3.7 from &quot;/usr/local/bin/python3&quot;
    * The NumPy version is: &quot;1.19.4&quot;
  
  and make sure that they are the versions you expect.
  Please carefully study the documentation linked above for further help.
  
  Original error was: /lib/arm-linux-gnueabihf/libm.so.6: version `GLIBC_2.27' not found (required by /home/pi/.local/lib/python3.7/site-packages/numpy/core/_multiarray_umath.cpython-37m-arm-linux-gnueabihf.so)
  </code></pre>
  <p><code>pip3 freeze</code> says that my numpy version is 1.19.4</p>
  <p><code>python3 --version</code> says that my python version is 3.7.0</p>
  <p>How can I fix this Problem?</p>