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Matplotlib crashes when importing pyplot in Blender

I know this question has been asked many times before but I cannot find a solution that works for me. I'm running Python 3.5.3 under Blender 2.79 in Windows 10. As I require Blender 2.79, upgrading the Python version is not possible.
I've installed matplotlib and I can import it. However, when I try to import pyplot (e.g. import matplotlib.pyplot as plt), I get a crash to desktop with no error messages of any kind. This happens if I run Python externally or from inside Blender. The weird thing is that I was able to avoid this by changing backends to agg (matplotlib.use('agg')) and this is still working in a previous installation (so I know it's possible to get this to work !), but not in a separate, new installation of Blender. I've tried other backends but they make no difference.
The exact procedure I've tried is as follows :
Downloaded Blender 2.79 from a zip file (I'm using Windows 10) and unpacked it (call this directory /Blender/)
In /Blender/2.79/python/bin I run the command ./python -m ensurepip
In /Blender/2.79/python/scripts I run pip3 install --upgrade pip --user. This gives me pip3 version 20.2.4
In the same directory I run pip3 install --target="/Blender/2.79/python/lib/site-packages" matplotlib --upgrade. The "upgrade" switch is to prevent warnings that the "/bin" directory exists. Doesn't make any difference if I remove it, there's no existing installation of matplotlib. This gives me matplotlib version 3.0.3
Finally I start Python by /Blender/2.79/python/bin/python.exe, and do the above mentioned importmatplotlib.pyplot command which causes the crash.
I've tried this from a completely fresh installation of Blender, which comes with no existing external modules installed. Could there be some conflict with other Python modules elsewhere ? How would I go about diagnosing what's going on ?
Thanks for any ideas !

FIXED ! I remembered I found the solution months ago, but stupidly wrote down the answer in the wrong file...
The problem is that matplotlib is looking for a file that doesn't exist. In c:/users/me/.matplotlib (a hidden file), there's a file ""fontlist-vXXX.json", where XXX is the version number. This is set in line 951 of the file "font_manager.py", located in /python/lib/site-packages/matplotlib. In my case, the font_manager was looking for version 300 but the actual file was 310. Changing the version number in the font_manager.py made everything work correctly.

Numpy installed, but module not found

I've tried several fixes for this suggested in other threads, but no luck.
I'm new to Python. I had 3.8.5 installed and wrote a few simple scripts that worked using PyCharm and the numpy and sympy modules. Today I opened PyCharm and tried to write a simple script using numpy, but I got an error saying the numpy module did not exist. I also got this error when trying to run the older scripts. I checked in cmd with pip3, and got the result that it was already satisfied. I uninstalled Python, numpy, and PyCharm, reinstalled all and I'm having the same problem. This problem seemed to crop up on its own - I don't recall making any changes that would've caused this.
Can anyone give me other options?

One of the most common issues with Python is having multiple versions installed and losing track of which one you are using and/or which one you're installing to with pip.
In Pycharm check what interpreter your project is using. If there is more than one available chance are you installed numpy on the other one.
https://www.jetbrains.com/help/pycharm/configuring-python-interpreter.html#add-existing-interpreter
You can also install numpy direct from Pycharm, simply hover over the import statement and if it's not installed on the current interpreter it will offer you a link to click in install it.
If that doesn't help, post the exact error message and your code.

How to fix 'ImportError: dynamic module does not define module export function (PyInit_cv2)' error in Python?

I'm running a code on deep learning, which uses the opencv module, by running python main.py (contains import cv2 statement), but always get the error 'ImportError: dynamic module does not define module export function (PyInit_cv2)'.
I've tried to reinstall my anaconda and create new virtual environments, but all got the same result. This problem really confuses me a lot and I've googled for many related problems, none of them works. I think the problem is something related to the environment and has nothing to do with the code, because I got the same result by simply run import cv2 in python prompt. The more confusing thing is that, even after I remove the opencv module, I also get the same problem, but not a ModuleNotFoundError. Does anyone can give me some advice? Thanks a lot!

I think I found one possible reason of this error.
Recently I was configuring the caffe environment on one server, I downloaded the source code of opencv-2.4.13 and compiled manually, added /usr/local/opencv-2.4.13/build/lib to $PYTHONPATH, and caffe worked well. After that, when I entered one of my virtual environment using conda activate py35, which uses python3.5, tried import cv2 in the python prompt, got the error above.
I'm not sure but I think the cause of the error is opencv-2.4.13 compiles a python2 interface so it can't be imported by python3. Python imports packages by searching the directories listed in sys.path, where $PYTHONPATH is in the second place after the current working directory (This is a great article introduces the mechanism of python finding packages). So when we enter the py35 environment, python will first look for $PYTHONPATH and find the opencv installed on the root directory instead of finding the opencv in the virtual environment using conda install opencv-python.
So there are two solutions of this problem:
Use python2 instead.
Remove /usr/local/opencv-2.4.13/build/lib from $PYTHONPATH.
which all work for me.

Similar post, might help:
ImportError: dynamic module does not define init function (initfizzbuzz)
Could you provide info on how you installed the CV module?

I had the same problem, which was caused by the cv2.so file in /usr/local/lib/python2.7/site-packages/cv2.so. After I deleted the file and use command sudo pip3 install opencv-python, it worked for python3.

Obnoxious CryptographyDeprecationWarning because of missing hmac.compare_time function everywhere

Things were running along fine until one of my projects started printing this everywhere, at the top of every execution, at least once:
local/lib/python2.7/site-packages/cryptography/hazmat/primitives/constant_time.py:26: CryptographyDeprecationWarning: Support for your Python version is deprecated. The next version of cryptography will remove support. Please upgrade to a 2.7.x release that supports hmac.compare_digest as soon as possible.
I have no idea why it started and it's disrupting the applications'/tools' output, especially when it's being captured and consumed by other tools. Like many difficulties throughout time, I'm fairly certain it is related to urllib and, by association, requests. Worse, I have so many projects and cross-dependencies that I can't possibly update all of the imports and branches with the call to warnings.filterwarnings() to suppress the warning.
I have Python 2.7.6 . Apparently this goes away in 2.7.7 . Only, I have some systems that have 2.7.6 where I do not see the warnings. So, something may or may not be disabling them in one version and I might've inadvertently replaced it with another version.
My Ubuntu, Python, urllib, requests (with the security option), cryptography, and hmac are all identical versions/builds on systems that do print the warning and systems that do not.
There appears to be no relevant warnings or announcements online and it seems like any related project is static/stable by this point (even though 'hmac' can be installed via PIP, it hasn't changed in eight years).

I hit this error for quite sometime. For my environment, it was a pain to upgrade Python to a higher version than 2.7.6. The easier solution was to downgrade cryptography module using pip:
pip2.7 install cryptography==2.2.2
I think the best solution is to upgrade your python version though

This answer is for Python3
I got here by looking for an answer while using Paramiko. For those still looking for a simple answer. I got these CryptographyDeprecationWarning suppresed with the these lines of code before importing Paramiko:
import warnings
warnings.filterwarnings(action='ignore',module='.*paramiko.*')
I hope this helps

If you want to be more selective about suppressing JUST that particular deprecation warning:
import warnings
from cryptography.utils import CryptographyDeprecationWarning
warnings.filterwarnings("ignore", category=CryptographyDeprecationWarning)

I started getting this warning for a straightforward requests.get call. This warning is printed when the module cryptography.hazmat.primitives.constant_time is loaded, and so this should typically only come once per Python program. If you are seeing it many times, it must be because a Python program (like a utility) is getting executed multiple times. You just have to identify that program and add the below code to the main entry point:
import cryptography
from cryptography import utils
with warnings.catch_warnings():
warnings.simplefilter('ignore', cryptography.utils.DeprecatedIn23)
import cryptography.hazmat.primitives.constant_time

I fixed this for all my local projects and tools using Python 2 by removing the warning from the python source code [your_installation_path]\Python\Lib\site-packages\cryptography\__init__.py
Just remove this snipped at the end of the file and delete the __init__.pyc file so its recompiled with the changes:
if sys.version_info[0] == 2:
warnings.warn(
"Python 2 is no longer supported by the Python core team. Support for "
"it is now deprecated in cryptography, and will be removed in the "
"next release.",
CryptographyDeprecationWarning,
stacklevel=2,
)

For Python3 only:
Per an apparent Paramiko update this worked for me and solve the similar problem/symptoms I was experiencing:
pip3 install --upgrade paramiko
This installed paramiko 2.6.0 on my system, replacing 2.4.2:
$ pip3 install --upgrade paramiko
[...]
Installing collected packages: paramiko
Found existing installation: paramiko 2.4.2
Uninstalling paramiko-2.4.2:
Successfully uninstalled paramiko-2.4.2
Successfully installed paramiko-2.6.0
$
My Python2 environment appears to be messed up, so I'm not able to test this on Python2.

When you do pip2.7 install cryptography==2.2.2, it appears the error might still occur.
I believe you need also sudo pip2.7 install --upgrade pip
Aso, as of 5/5/19 the newest appears to be cryptography=2.6.1

Installing mesos egg for python 2.7

I've installed mesos 0.26 successfully on a vm machine.
The installation has been performed on an ubuntu trusty thar system
by following this manual:
https://open.mesosphere.com/getting-started/install/
So far so good. I wanted to write a tiny python framwork.
For this I need to install the eggs via easy_install:
(I've downloaded the eggs accordingly for the trusty thar ubuntu and the 0.26 mesos):
wget http://downloads.mesosphere.io/master/ubuntu/14.04/mesos-0.26.0-py2.7-linux-x86_64.egg
easy_install mesos-0.26.0-py2.7-linux-x86_64.egg
all went fine, however, if I start python in the shell
and type in
import mesos.interface
I get the message: ImportError: No module named interface
As someone suggested, it may be that there is no longer a binding for python, or that they have renamed the API calls. Well, I looked in the version updates here:
http://mesos.apache.org/documentation/latest/upgrades/
Since the transition from 0.19.x to 0.20.x there hasn't been any changes regarding the mesos.interface part, or at least they are not mentioning it here.
To increase the confusion I also get the following error message when I'm typing in python: import mesos.native
There I receive: ImportError: No module named interface.mesos_pb2. To put it into a nutshell: what is going wrong here, and how can it be fixed? And yes, I've googled various web pages, with terms such as "mesos python bindings", mesos +api +python, etc. And yes, I have also consulted the official mesos webpage. There are nice refences for Java and C++ but not for python, or at least they are very well hidden.
Thanks in advance for any hints.

Solved. For what reasons ever:
export PYTHONPATH=${PYTHONPATH}:/usr/lib/python2.7/site-packages/
is required to set the PYTHONPATH. After that step it works like a charm.