Setting Up Python For Linux¶

Python¶

Debian distros already have the stable python2 and python3 releases preinstalled [1]. Try the following commands:

$ python2
Python 2.7.9 (default, April 2 2015, 15:33:32)
[GCC 4.9.2 on linux2]
>>>

$ python3
Python 3.4.3 (default, March 26 2015, 15:33:32)
[GCC 4.9.2 on linux]
>>>

I’m pretty sure that 16.4 (the most recent long term support release) has 3.5

That’s nice, which one is the default version? Just type python to see. It’s probably python2 still:

$ python
Python 2.7.9 (default, April 2 2015, 15:33:32)
[GCC 4.9.2 on linux2]
>>>

If you want to make python3.5 the default version then add the line alias python=python3 to your user’s /home/{user}/.bashrc file like so:

$ # before the change
$ python
Python 2.7.9 (default, April 2 2015, 15:33:32)
[GCC 4.9.2 on linux2]
>>>

$ echo "alias python=python3" >> ~/.bashrc
$ source ~/.bashrc

$ # after the change
$ python
Python 3.4.3 (default, March 26 2015, 15:33:32)
[GCC 4.9.2 on linux]
>>>

If you don’t have the version you want installed then use the package manager to find and install it:

$ # search the package manager for it
$ sudo apt-cache search python | grep '^python3.5\ -'
python3.5 - Interactive high-level object-oriented language (version 3.5)
$ # install it
$ sudo apt-get install python3.5

Terminal¶

Every Linux box has a terminal emulator – find and use it.

git¶

Git is likely to be there on your system already, but if not:

$ sudo apt-get install git

pip¶

pip is the Python package installer.

Many python packages are also available directly from your distro – but you’ll get the latest and greatest if you use pip to install it instead.

To get pip, the first option is to use your system package manager, something like:

$ sudo apt-get install python3-pip

If that doesn’t work, then look up the official manual install notes

Using pip:¶

To use pip to install a package, you invoke it with this command:

python -m pip install the_name_of_the_package

Where python is the command you use to invoke the python you want to use (could be python3)

NOTE: You will frequently see advice to use pip like so:

$ pip install something_or_other

Which often works, but also can invoke the wrong version of pip. The above command:

$ python -m pip install something_or_other

calls python, and tells it to run the pip module. It is exactly the same as calling pip directly, except that you are assured that you are getting the version of pip connected the version of python that you are running.

iPython¶

One extra package we are going to use in class is iPython:

$ sudo python3 -m pip install ipython[all]

You should now be able to run iPython:

$ ipython3
Python 3.5.2 ()
Type "copyright", "credits" or "license" for more information.

IPython 2.0.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

Python¶

Fedora distros already have the stable python2 and python3 releases preinstalled [2]. However, CentOS, the most popular distro only has the stable python2 release. Try the following commands:

[centos@ip-172-31-21-5 ~]$ python2
Python 2.7.5 (default, Jun 17 2014, 18:11:42)
[GCC 4.8.2 20140120 (Red Hat 4.8.2-16)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>

[centos@ip-172-31-21-5 ~]$ python3
-bash: python3: command not found

Let’s install python3 using the package manager. Step one install “Software Collections” to help us:

$ sudo yum -y install scl-utils

Then go to the software collections listing and click on the python collection version you want to install.

Probably this one:

https://www.softwarecollections.org/en/scls/rhscl/rh-python35/

Note, you also need to know which version of CentOS you are using (probably 6 or 7). For example, we care about python version 3.5 so let’s go the .rpm i want to install here:

$ # add this package to the rpm package manager
$ sudo rpm -Uvh https://www.softwarecollections.org/repos/rhscl/rh-python34/epel-7-x86_64/noarch/rhscl-rh-python35-epel-7-x86_64.noarch.rpm

$ # install the right python version
$ sudo yum install rh-python35

When you want to use python3 run this command:

[centos@ip-172-31-21-5 ~]$ scl enable rh-python35 bash

Terminal¶

Every Linux box has a terminal emulator – find and use it.

git¶

Git is likely to be there on your system already, but if not:

$ sudo yum install git

pip¶

pip is the Python package installer.

Many python packages are also available directly from your distro – but you’ll get the latest and greatest if you use pip to install it instead.

In CentOS, if you used the above technique to install Python3, then it comes with pip. Try:

[centos@ip-172-31-21-5 ~]$ python -m pip -V
pip 8.1.2 from /opt/rh/rh-python35/root/usr/lib/python3.5/site-packages (python 3.5)

Using pip:¶

To use pip to install a package, you invoke it with this command:

python -m pip install the_name_of_the_package

Where python is the command you use to invoke the python you want to use (could be python3)

NOTE: You will frequently see advice to use pip like so:

$ pip install something_or_other

Which often works, but also can invoke the wrong version of pip. The above command:

$ python -m pip install something_or_other

calls python, and tells it to run the pip module. It is exactly the same as calling pip directly, except that you are assured that you are getting the version of pip connected the version of python that you are running.

iPython¶

One we are going to use in class is iPython:

$ sudo pip install ipython[all]

You should now be able to run iPython:

$ ipython3
    Python 3.5.2 ()
    Type "copyright", "credits" or "license" for more information.

    IPython 5.1.0 -- An enhanced Interactive Python.
    ?         -> Introduction and overview of IPython's features.
    %quickref -> Quick reference.
    help      -> Python's own help system.
    object?   -> Details about 'object', use 'object??' for extra details.