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Missing MySql driver when using PySide2 QtSql QSqlDatabase

I'm porting some code from PySide to PySide2 and I've noticed that I'm missing a couple of sql drivers.
$ python3
Python 3.6.8 (default, Apr 2 2020, 13:34:55)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-39)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import PySide.QtSql; import PySide2.QtSql
>>> PySide.QtSql.QSqlDatabase.drivers()
['QSQLITE', 'QSQLITE3', 'QMYSQL3', 'QMYSQL', 'QODBC3', 'QODBC', 'QPSQL7', 'QPSQL']
>>> PySide2.QtSql.QSqlDatabase.drivers()
['QSQLITE', 'QODBC', 'QODBC3', 'QPSQL', 'QPSQL7']
As you can see I'm missing QMYSQL on PySide2 (among others). I need that one for my application to work.
I've tried installing a couple of packages like mysql mysql-connector-python through pip but that didn't change anything. Then I tried changing QTDIR because I noticed it was pointing to /usr/lib64/qt-3.3 instead of /usr/lib64/qt5. That didn't do anything either.
I also checked /usr/lib64/qt4/plugins/sqldrivers and /usr/lib64/qt5/plugins/sqldrivers for libqsqlmysql.so and it's present in both folders.
I'm on CentOS 7 by the way. I'm trying to get the software on CentOS 7 and 8, though.
Pretty much all of the posts I've seen about it the drivers aren't missing but they can't be loaded.
Any idea what could be the problem?

Most likely, the plugin directory is not in "/usr/lib64/qt5/plugins" so it doesn't load the mysql plugin. The solution is to copy the plugin so the first thing is to know the PySide2 directory plugin by executing the following command:
$ python3 -c "from PySide2 import QtCore; print(QtCore.QLibraryInfo.location(QtCore.QLibraryInfo.PluginsPath))"
Output:
/usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins
So you should copy the .so using the following command:
$ cp /usr/lib64/qt5/plugins/sqldrivers/libqsqlmysql.so /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers
Even so the .so points to the Qt of the OS instead of the Qt of PySide2:
$ ldd /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/libqsqlmysql.so
Output
linux-vdso.so.1 => (0x00007fffb974f000)
libQt5Sql.so.5 => /lib64/libQt5Sql.so.5 (0x00007faa76f00000)
libQt5Core.so.5 => /lib64/libQt5Core.so.5 (0x00007faa76895000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007faa76679000)
libmysqlclient.so.18 => /usr/lib64/mysql/libmysqlclient.so.18 (0x00007faa76179000)
# ...
for this you must change the rpath using patchelf:
$ yum install epel-release
$ yum install patchelf
$ patchelf --set-rpath \$ORIGIN/../../lib /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/libqsqlmysql.so
again:
$ ldd /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/libqsqlmysql.so
Output
linux-vdso.so.1 => (0x00007ffd013ad000)
libQt5Sql.so.5 => /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/../../lib/libQt5Sql.so.5 (0x00007f6e1fb4c000)
libQt5Core.so.5 => /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/../../lib/libQt5Core.so.5 (0x00007f6e1f359000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f6e1f13d000)
libmysqlclient.so.18 => /usr/lib64/mysql/libmysqlclient.so.18 (0x00007f6e1ec3d000)
# ...
Finally:
$ python3 -c "from PySide2 import QtSql; print(QtSql.QSqlDatabase.drivers())"
Output:
['QSQLITE', 'QMYSQL', 'QMYSQL3', 'QODBC', 'QODBC3', 'QPSQL', 'QPSQL7']
It seems that there is no binary compatibility between the plugins so it must be compiled using the source code:
$ python3 -m pip install aqtinstall
$ python3 -m aqt install 5.15.0 linux desktop --outputdir qt
$ sudo yum -y install git
$ sudo yum -y install libxcb libxcb-devel xcb-util xcb-util-devel xcb-util-*-devel libX11-devel libXrender-devel libxkbcommon-devel libxkbcommon-x11-devel libXi-devel libdrm-devel libXcursor-devel libXcomposite-devel
$ sudo yum -y install centos-release-scl
$ sudo yum -y install devtoolset-7-gcc*
$ sudo yum -y groupinstall 'Development Tools'
$ sudo yum -y install mysql-devel
$ scl enable devtoolset-7 bash
$ git clone -b 5.15.0 git://code.qt.io/qt/qtbase.git
$ cd qtbase/src/plugins/sqldrivers/mysql
$ sed -i 's/QMAKE_USE += mysql/# QMAKE_USE += mysql/g' mysql.pro
$ echo "INCLUDEPATH += /usr/include/mysql" >> mysql.pro
$ echo "QMAKE_LIBDIR += /usr/lib64/mysql" >> mysql.pro
$ echo "LIBS += -lmysqlclient" >> mysql.pro
$ ../../../../../qt/5.15.0/gcc_64/bin/qmake
$ make
$ sudo cp ../plugins/sqldrivers/libqsqlmysql.so /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers
Finally:
$ python3 -c "from PySide2 import QtSql; print(QtSql.QSqlDatabase.drivers())"
Output:
['QSQLITE', 'QMARIADB', 'QMYSQL', 'QMYSQL3', 'QODBC', 'QODBC3', 'QPSQL', 'QPSQL7']

Alpine error during installing python shapely

I need to install Shapely into Python+Alpine based docker container. What I already have inside the container:
make, gcc, geos-dev, musl-dev
What I got with this command:
pip install shapely
Collecting shapely
Downloading https://files.pythonhosted.org/packages/a2/fb/7a7af9ef7a35d16fa23b127abee272cfc483ca89029b73e92e93cdf36e6b/Shapely-1.6.4.post2.tar.gz (225kB)
|████████████████████████████████| 235kB 641kB/s
ERROR: Command errored out with exit status 1:
command: /usr/local/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-vj51jvsy/shapely/setup.py'"'"'; __file__='"'"'/tmp/pip-install-vj51jvsy/shapely/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-install-vj51jvsy/shapely/pip-egg-info
cwd: /tmp/pip-install-vj51jvsy/shapely/
Complete output (11 lines):
Failed `CDLL(libgeos_c.so.1)`
Failed `CDLL(libgeos_c.so)`
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/tmp/pip-install-vj51jvsy/shapely/setup.py", line 80, in <module>
from shapely._buildcfg import geos_version_string, geos_version, \
File "/tmp/pip-install-vj51jvsy/shapely/shapely/_buildcfg.py", line 167, in <module>
fallbacks=['libgeos_c.so.1', 'libgeos_c.so'])
File "/tmp/pip-install-vj51jvsy/shapely/shapely/_buildcfg.py", line 161, in load_dll
libname, fallbacks or []))
OSError: Could not find library geos_c or load any of its variants ['libgeos_c.so.1', 'libgeos_c.so']
----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.
I googled around much time but can't find any solving.
Dockerfile
FROM python:3.7-alpine
RUN ["mkdir", "/home/test"]
WORKDIR /home/test
RUN echo "http://mirror.leaseweb.com/alpine/edge/testing" >> /etc/apk/repositories
RUN echo "http://dl-cdn.alpinelinux.org/alpine/edge/testing" >> /etc/apk/repositories
RUN ["apk", "add", "make", "gcc", "geos-dev", "musl-dev"]
RUN ["pip3", "install", "virtualenv", "--no-warn-script-location", "--disable-pip-version-check"]
RUN ["virtualenv", ".env", "--python=python3"]
RUN ["pip3", "install", "shapely"]
CMD ["/bin/sh"]
Version of Python inside the container
/home/test # /usr/local/bin/python
Python 3.7.5 (default, Oct 21 2019, 20:13:45)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
GEOS version
/home/test # geos-config --version
3.7.2
UPDATED
Now you must put this repo beneath others:
--repository http://dl-cdn.alpinelinux.org/alpine/edge/community

This will work:
FROM python:3.7-alpine
RUN ["mkdir", "/home/test"]
WORKDIR /home/test
RUN echo "http://mirror.leaseweb.com/alpine/edge/community" >> /etc/apk/repositories
RUN echo "http://dl-cdn.alpinelinux.org/alpine/edge/community" >> /etc/apk/repositories
RUN apk add --virtual .build-deps \
--repository http://dl-cdn.alpinelinux.org/alpine/edge/community \
--repository http://dl-cdn.alpinelinux.org/alpine/edge/main \
gcc libc-dev geos-dev geos && \
runDeps="$(scanelf --needed --nobanner --recursive /usr/local \
| awk '{ gsub(/,/, "\nso:", $2); print "so:" $2 }' \
| xargs -r apk info --installed \
| sort -u)" && \
apk add --virtual .rundeps $runDeps
RUN ["pip", "install", "shapely"]
CMD ["/bin/sh"]
see this
UPDATE: As per comments, geos-dev has moved to the community repo.

I hit this problem with my build as well. My workaround was to switch from Alpine to Debian (not ideal, but it allowed me to use an older version of geos), since it appears the latest version of geos is incompatible with shapely.

pip not installing numba/llvmlite properly within conda environment

I create a new conda environment
user#machine:~/project$ conda create -n test-env -c numba python=3.5.2 llvmdev=3.8
Fetching package metadata ...........
Solving package specifications: .
Package plan for installation in environment /home/user/anaconda2/envs/test-env:
The following NEW packages will be INSTALLED:
llvmdev: 3.8.1-7 numba
openssl: 1.0.2k-0
pip: 9.0.1-py35_1
python: 3.5.2-0
readline: 6.2-2
setuptools: 27.2.0-py35_0
sqlite: 3.13.0-0
system: 5.8-2 numba
tk: 8.5.18-0
wheel: 0.29.0-py35_0
xz: 5.2.2-1
zlib: 1.2.8-3
Proceed ([y]/n)? y
#
# To activate this environment, use:
# > source activate test-env
#
# To deactivate this environment, use:
# > source deactivate test-env
#
and then activate it and attempt to use specifically pip (not conda) to install llvmlite and numba, which appears to succeed. (Note: I've tried also --no-cache-dir and it doesn't change anything.)
user#machine:~/project$ source activate test-env
(test-env) user#machine:~/project$ pip install llvmlite==0.15 numba==0.30.1
Collecting llvmlite==0.15
Collecting numba==0.30.1
Collecting numpy (from numba==0.30.1)
Using cached numpy-1.12.0-cp35-cp35m-manylinux1_x86_64.whl
Installing collected packages: llvmlite, numpy, numba
Successfully installed llvmlite-0.15.0 numba-0.30.1 numpy-1.12.0
But the library is not installed properly,
(test-env) user#machine:~/project$ python
Python 3.5.2 |Continuum Analytics, Inc.| (default, Jul 2 2016, 17:53:06)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import numba
Traceback (most recent call last):
File "/home/user/anaconda2/envs/test-env/lib/python3.5/site-packages/llvmlite/binding/ffi.py", line 42, in <module>
lib = ctypes.CDLL(os.path.join(_lib_dir, _lib_name))
File "/home/user/anaconda2/envs/test-env/lib/python3.5/ctypes/__init__.py", line 347, in __init__
self._handle = _dlopen(self._name, mode)
OSError: /home/user/anaconda2/envs/test-env/lib/python3.5/site-packages/llvmlite/binding/libllvmlite.so: undefined symbol: _ZNKSt14error_category23default_error_conditionEi
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/user/anaconda2/envs/test-env/lib/python3.5/site-packages/numba/__init__.py", line 9, in <module>
from . import config, errors, runtests, types
File "/home/user/anaconda2/envs/test-env/lib/python3.5/site-packages/numba/config.py", line 11, in <module>
import llvmlite.binding as ll
File "/home/user/anaconda2/envs/test-env/lib/python3.5/site-packages/llvmlite/binding/__init__.py", line 6, in <module>
from .dylib import *
File "/home/user/anaconda2/envs/test-env/lib/python3.5/site-packages/llvmlite/binding/dylib.py", line 4, in <module>
from . import ffi
File "/home/user/anaconda2/envs/test-env/lib/python3.5/site-packages/llvmlite/binding/ffi.py", line 47, in <module>
lib = ctypes.CDLL(_lib_name)
File "/home/user/anaconda2/envs/test-env/lib/python3.5/ctypes/__init__.py", line 347, in __init__
self._handle = _dlopen(self._name, mode)
OSError: libllvmlite.so: cannot open shared object file: No such file or directory
Why does the conda installation of llvmdev from the numba channel fail to "just work".
In my use case, I'm coming to a project that has a pip-styled requirements.txt file, and I need to create conda environments from that file. Some project developers will use venv+pip, some will use conda, and some packages it contains are not found in any anaconda channels, so pip installation is mandatory. We don't want to maintain a separate envrionment.yaml in addition to the requirements.txt, so installing from requirements.txt inside of a conda envrionment is part of my constraints.
Everything seems OK, except for the pip installation of numba/llvmlite, which expects a system dependency of llvm 3.8+. I want to satisfy that as part of the conda environment though.
How can I ensure from a conda environment only that the right llvmdev exists for installing numba and llvmlite?

Installing llvmdev:
Installing llvmdev from the conda-forge channel can be achieved by adding conda-forge to your channels with:
conda config --add channels conda-forge
Once the conda-forge channel has been enabled, llvmdev can be installed with:
conda install llvmdev
It is possible to list all of the versions of llvmdev available on your platform with:
conda search llvmdev --channel conda-forge
HELP:I cloned the relevant files from their GitHub sources and did
python setup.py install
for more without conda use pip
sudo pip install -U llvmlite
sudo pip install -U numba

This is what worked for me using the Anaconda environment:
pip uninstall llvmlite
pip install -U --ignore-installed numba

In an ideal scenario, the required shared library should be present after the installation of llvmlite.
(test-env) ~/condaexpts$ conda create -n test-env -c numba python=3.5.2 llvmdev=3.8
(test-env) ~/condaexpts$ source activate test-env
(test-env) ~/condaexpts$ pip install numpy==1.12.0 llvmlite==0.15 numba==0.30.1
(test-env) ~/condaexpts$ find $CONDA_PREFIX | grep libllvmlite
/home/ubuntu/condaexpts/m3/envs/test-env/lib/python3.5/site-packages/llvmlite/binding/libllvmlite.so
If this file is not present in the test-env, then something went wrong while installing llvmlite.
Also, think about this approach the other way round. You don't need to have a requirements file separate from conda environment file. You can have both dependencies in the conda environment file itself:
(test-env) ~/condaexpts$ conda env export
name: test-env
channels:
- !!python/unicode
'numba'
- !!python/unicode
'defaults'
dependencies:
- !!python/unicode
'openssl=1.0.2k=0'
- !!python/unicode
'pip=9.0.1=py35_1'
- !!python/unicode
'python=3.5.2=0'
- !!python/unicode
'readline=6.2=2'
- !!python/unicode
'setuptools=27.2.0=py35_0'
- !!python/unicode
'sqlite=3.13.0=0'
- !!python/unicode
'tk=8.5.18=0'
- !!python/unicode
'wheel=0.29.0=py35_0'
- !!python/unicode
'xz=5.2.2=1'
- !!python/unicode
'zlib=1.2.8=3'
- !!python/unicode
'llvmdev=3.8.1=7'
- !!python/unicode
'system=5.8=2'
- pip:
- llvmlite==0.15.0
- numba==0.30.1
- numpy==1.12.0
prefix: !!python/unicode '/home/ubuntu/condaexpts/m3/envs/test-env'
On second note, you can install the pre-built binaries required from the 'numba' conda channel itself. With:
(root) ~/condaexpts$ ./Miniconda3-latest-Linux-x86_64.sh -b -p m3
(root) ~/condaexpts$ source ./m3/bin/activate
(root) ~/condaexpts$ conda create -n test-env -c numba python=3.5.2 llvmdev=3.8 numba=0.30.1 llvmlite=0.15.0
(root) ~/condaexpts$ source activate test-env
(test-env) ~/condaexpts$ python
Python 3.5.2 |Continuum Analytics, Inc.| (default, Jul 2 2016, 17:53:06)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import numba
>>> numba.__version__
'0.30.1'

error occurs when installing pip

I don't know what to do next to fix? All the things are in red!
this is what shows when I conducted the final step using : python get-pip.py
I just follow the instructions getting from
Exception:
Traceback (most recent call last):
.....(too long)
conn = self.get_connection(request.url, proxies)
File "/tmp/tmpGK7Hjj/pip.zip/pip/_vendor/requests/adapters.py", line 290, in get_connection
proxy_manager = self.proxy_manager_for(proxy)
File "/tmp/tmpGK7Hjj/pip.zip/pip/_vendor/requests/adapters.py", line 184, in proxy_manager_for
**proxy_kwargs
File "/tmp/tmpGK7Hjj/pip.zip/pip/_vendor/requests/packages/urllib3/contrib/socks.py", line 154, in __init__
"Unable to determine SOCKS version from %s" % proxy_url
ValueError: Unable to determine SOCKS version from socks://10.77.8.70:8080/
This is what shows when enter
whereis python?
python: /usr/bin/python2.7 /usr/bin/python3.5m /usr/bin/python /usr/bin /python2.7-config /usr/bin/python3.5 /usr/lib/python2.7 /usr/lib/python3.5 /etc/python2.7 /etc/python /etc/python3.5 /usr/local/lib/python2.7 /usr/local/lib/python3.5 /usr/include/python2.7 /usr/share/python /usr/share/man/man1/python.1.gz
whereis pip?
pip: /usr/local/bin/pip3.5 /usr/local/bin/pip /usr/local/bin/pip2.7
Thank you very much!

To intsall pip for Python2 use the following command:
sudo apt-get install python-pip
For Python3 use
sudo apt-get install python3-pip

'EntryPoint' object has no attribute 'resolve' when using Google Compute Engine

I have an issue related to Cryptography package in Python. Can you please help in resolving these, if possible ? (tried a lot, but couldnt figure out the exact solution)
The python code which initiates this error:
print("Salt: %s" % salt)
server_key = pyelliptic.ECC(curve="prime256v1") # ----->> Line2
print("Server_key: %s" % server_key) # ----->> Line3
server_key_id = base64.urlsafe_b64encode(server_key.get_pubkey()[1:])
http_ece.keys[server_key_id] = server_key
http_ece.labels[server_key_id] = "P-256"
encrypted = http_ece.encrypt(data, salt=salt, keyid=server_key_id,
dh=self.receiver_key, authSecret=self.auth_key) # ----->> Line8
Value of "Salt" is getting displayed in 100% of the cases.
If Line3 gets executed successfully, I see the the following EntryPoint Error because of http_ece.encrypt() call (Line8):
AttributeError("'EntryPoint' object has no attribute 'resolve'",)
(Ref. File Link: https://github.com/martinthomson/encrypted-content-encoding/blob/master/python/http_ece/init.py#L128 )
Requirements.txt(partial):
cryptography==1.5
pyelliptic==1.5.7
pyOpenSSL==16.1.0
On Running the command: sudo pip freeze --all |grep setuptools, I get:
setuptools==27.1.2
Please let me know if any more detail is required.
This problem seems to be basically due to some Old/Incompatible packages(related to PyElliptic, Cryptography, PyOpenSSL and/or setuptools) installed on the VM. For Reference: https://github.com/pyca/cryptography/issues/3149
Can someone please suggest a good solution to resolve this issue completely ?
Thanks,

The issue referenced in c66303382 has this traceback (you never gave your traceback so I have to assume yours ends the same way):
File "/usr/local/lib/python2.7/dist-packages/cryptography/hazmat/backends/__init__.py", line 35, in default_backend
_default_backend = MultiBackend(_available_backends())
File "/usr/local/lib/python2.7/dist-packages/cryptography/hazmat/backends/__init__.py", line 22, in _available_backends
"cryptography.backends"
The full line that triggers the error looks like this:
_available_backends_list = [
ep.resolve()
for ep in pkg_resources.iter_entry_points(
"cryptography.backends"
)
]
Searching the repository for EntryPoint definition, then blaming pkg_resources/__init__.py where it is reveals that pkg_resources.EntryPoint.resolve() was added in commit 92a553d3adeb431cdf92b136ac9ccc3f2ef98bf1 (2015-01-05) that went into setuptools v11.3.
Thus you'll see this error if you use an older version.

Ran Following Commands from the project path /opt/projects/myproject-google/myproject and it resolved the Attribute EntryPoint Error Issue:
(Assuming project virtual env path as: /opt/projects/myproject-google/venv)
Command: (from path: /opt/projects/myproject-google/myproject)
export PYTHONPATH= # [Blank]
sudo pip install --upgrade virtualenv setuptools
sudo rm -rf ../venv
sudo virtualenv ../venv
source ../venv/bin/activate
sudo pip install --upgrade -r requirements.txt
deactivate
Running the above commands upgraded the virtual environment & the setuptools version inside the virtual Env. located at path: /opt/projects/myproject-google/venv/lib/python2.7/site-packages. To test if setuptools have upgraded successfully, try some of these commands:
Command: sudo virtualenv --version
Output: 15.0.3
Command: echo $PYTHONPATH
Output: [blank]
Command: python -c 'import pkg_resources; print(pkg_resources.__file__)'
Output: ~/.local/lib/python2.7/site-packages/pkg_resources/__init__.pyc
Command: python -c 'import sys; print(sys.path)'
Output: ['', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-x86_64-linux-gnu', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '~/.local/lib/python2.7/site-packages', '/usr/local/lib/python2.7/dist-packages', '/opt/projects/myproject-google/myproject', '/usr/local/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages/PILcompat']
Command: ls /opt/projects/myproject-google/venv/lib/python2.7/site-packages
Output:
easy_install.py pip pkg_resources setuptools-27.2.0.dist-info wheel-0.30.0a0.dist-info
easy_install.pyc pip-8.1.2.dist-info setuptools wheel
Command: python -c 'from cryptography.hazmat.backends import default_backend; print(default_backend())'
Output: <cryptography.hazmat.backends.multibackend.MultiBackend object at 0x7ff83a838d50>
Command /opt/projects/myproject-google/venv/bin/python -c 'from cryptography.hazmat.backends import default_backend; print(default_backend())'
Output
Traceback (most recent call last):
File "<string>", line 1, in <module>
ImportError: No module named cryptography.hazmat.backends
Command: /opt/projects/myproject-google/venv/bin/python -c "import pkg_resources; print(pkg_resources.__file__)"
Output: /opt/projects/myproject-google/venv/local/lib/python2.7/site-packages/pkg_resources/__init__.pyc
Ref Link: https://github.com/pyca/cryptography/issues/3149
These Steps resolved the Attribute EntryPoint Issue completely with an updated version of cryptography package & the setuptools.
Update As on 15 September 2016, The Cryptography Team has again added the workaround for supporting old packages too.
(Ref. Link: https://github.com/pyca/cryptography/issues/3150 )