Python3 [wiki.dlma]

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====== Python3 ======

If I want Python 3.7, I have to compile it myself.  Use "dnf" for RedHat based distros and "apt-get" for Debian.

===== RedHat based distros =====

<code bash>
sudo dnf install readline-devel  # or up-arrow won't navigate history
sudo dnf install sqlite-devel openssl-devel bzip2-devel
sudo dnf install xz-devel
</code>

Then on Fedora and CentOS...

<code bash>
wget https://www.python.org/ftp/python/3.7.0/Python-3.7.0.tgz
tar -xvf Python-3.7.0.tgz
cd Python-3.7.0/
./configure --prefix=/usr/local/bin/python3.7 --enable-optimizations
make
sudo make install
# sudo ln -s /usr/local/bin/python3.7/bin/python3 /usr/bin/python3
</code>

On my dev system at work, I seem to have configured a prefix like /opt/python3. Then when CentOS updates itself, it changes a symbolic link in /usr/bin/python3

    sudo rm /usr/bin/python3 && sudo ln -s /opt/python3/bin/python3 /usr/bin/python3

For **OS X**, brew upgrading httpie seems to upgrade to the latest Python 3, so I didn't have to do stuff.

===== Debian based distros (Start) =====

For Debian (eg., Rasbian) try [[http://www.unixmen.com/howto-install-python-3-x-in-ubuntu-debian-fedora-centos/|the following]] (on raspberry pi libssl-dev isn't available):

<code bash>
sudo apt-get install build-essential libncursesw5-dev libreadline-dev libssl-dev libgdbm-dev libc6-dev libsqlite3-dev tk-dev libffi-dev
</code>

==== (Aside) OpenSSL 1.0.1 issue in Raspbian ====

On Raspbian Jessie the make command (below) may have output that looks like this:

<code>
The necessary bits to build these optional modules were not found:
_bz2                  _lzma                 _ssl
</code>

On Raspbian, the pip module may not work because it relies on the ssl module.

<code>
pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available.
</code>

Python's setup.py explains:

> Python requires an OpenSSL 1.0.2 or 1.1 compatible libssl with X509_VERIFY_PARAM_set1_host().

If you check the version of ssh:

<code>
$ openssl version
OpenSSL 1.0.1t  3 May 2016
</code>

That OpenSSL is too old. So you may have to [[https://raspberrypi.stackexchange.com/questions/66782/how-to-install-openssl-1-0-2-on-raspberry-pi3/67045|make your own OpenSSL library]].

<code bash>
# Add the backport apt source.
echo "deb-src http://httpredir.debian.org/debian jessie-backports main contrib non-free" | \
      sudo tee /etc/apt/sources.list.d/jessie-backports.list
sudo apt update

# Get the openssl source
apt-get source openssl/jessie-backports

# Make and install it.
cd openssl-1.0.2k/
./config --prefix=/usr
make
make test
sudo make install
</code>

**Update**: The following apt-cache policy command showed the old libssl was still installed. It's probably bad, but I [[https://my-take-on.tk/2018/09/10/installing-latest-python-3x-and-pip-on-any-debian-based-system/|installed the new one with apt install -t jessie-backports]].

<code>
sudo apt-cache policy libssl-dev
</code>

===== Debian based distros (Continued) =====

Then, back to Python3, on Raspbian, I put it in the default location, /usr/local:

<code bash>
screen  # Because using optimizations will take hours
cd Python-3.7.0/
./configure --enable-optimizations
make -j4
sudo make install
[[ $TERM != "screen" ]] || exit  # exit if in screen session
</code>

===== Modules =====

Sometimes I have trouble with pip3 (ImportError: cannot import name 'main' from 'pip'), so prefer to use "python3 -m pip" instead.

<code bash>
sudo -H python3 -m pip install --upgrade pip
sudo -H python3 -m pip install requests
sudo -H python3 -m pip install numpy
sudo -H python3 -m pip install matplotlib
python3 -m pip install --user --upgrade httpie
</code>

===== Weird hack for impyla =====

Refers to https://stackoverflow.com/questions/43918993/python-buildpack-fatal-error-sasl-sasl-h-no-such-file-or-directory

<code bash>
sudo python3 -m pip install --no-deps impyla
sudo python3 -m pip install --no-deps git+https://github.com/snowch/thrift_sasl
# sudo python3 -m pip install thriftpy
</code>

===== MatPlotLib =====

There's another note on MatPlotLib over at my [[wsl]] page. For the first time on a Macintosh, I had to set the MatPlotLib backend to 'MacOSX'. Otherwise the plot window would appear but not draw any lines.

<code python>
import matplotlib
matplotlib.use('MacOSX')
</code>