Update Python on Linux 2.7 to 3.5

Update python on linux 2.7 to 3.5

You still have Python 2 installed, and the python command is still set up to invoke that version by default.
Try running your scripts like this:

python3 yourscriptname.py

In /usr/bin/, "python" is actually a symlink to python2.7. If you'd rather not have to type the 3 at the end whenever you use python, change that symlink to point to python3 instead. Then python will run Python 3.5 and you can use python2.7 or just python2 to run Python 2.7 scripts.

EDIT: Alternatively, you could put alias python=python3 in your ~/.bashrc file to do the same thing, but without needing root access and for your user account only.

Is it ok to install both Python 2.7 and 3.5?

I have installed two versions, 2.7, 3.4 and I do not have any problem by now. 3.4 I am using for my work project in eclipse environment, 2.7 for udacity course, like You ;).

How do I upgrade the Python installation in Windows 10?

Every minor version of Python, that is any 3.x and 2.x version, will install side-by-side with other versions on your computer. Only patch versions will upgrade existing installations.

So if you want to keep your installed Python 2.7 around, then just let it and install a new version using the installer. If you want to get rid of Python 2.7, you can uninstall it before or after installing a newer version—there is no difference to this.

Current Python 3 installations come with the py.exe launcher, which by default is installed into the system directory. This makes it available from the PATH, so you can automatically run it from any shell just by using py instead of python as the command. This avoids you having to put the current Python installation into PATH yourself. That way, you can easily have multiple Python installations side-by-side without them interfering with each other. When running, just use py script.py instead of python script.py to use the launcher. You can also specify a version using for example py -3 or py -3.6 to launch a specific version, otherwise the launcher will use the current default (which will usually be the latest 3.x).

Using the launcher, you can also run Python 2 scripts (which are often syntax incompatible to Python 3), if you decide to keep your Python 2.7 installation. Just use py -2 script.py to launch a script.

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As for PyPI packages, every Python installation comes with its own folder where modules are installed into. So if you install a new version and you want to use modules you installed for a previous version, you will have to install them first for the new version. Current versions of the installer also offer you to install pip; it’s enabled by default, so you already have pip for every installation. Unless you explicitly add a Python installation to the PATH, you cannot just use pip though. Luckily, you can also simply use the py.exe launcher for this: py -m pip runs pip. So for example to install Beautiful Soup for Python 3.6, you could run py -3.6 -m pip install beautifulsoup4.

Unable to set default python version to python3 in ubuntu

EDIT:

I wrote this when I was young and naive, update-alternatives is the better way to do this. See @Pardhu's answer.

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Outdated answer:

Open your .bashrc file nano ~/.bashrc. Type alias python=python3
on to a new line at the top of the file then save the file with ctrl+o
and close the file with ctrl+x. Then, back at your command line type
source ~/.bashrc. Now your alias should be permanent.

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