Ubuntu 16: Confusion regarding Python 2.7 and Python 3.x

Question

I have gone through the related questions and their answers. Still I am asking this question.

1. If a change the alias to Python 3.x, will the system break.
2. There are two pip files in\usr\bin directory. pip and pip2. I don't know which one to use to get modules and packages.
3. pandas is installed but import pandas in Python 2 works properly. But not in Python 3.x
4. pip install pandas gives an error while pip2 install pandas is telling that pandas is already installed.

Due to the above reasons, I am not able to work in Python in my Linux box (Ubuntu 16.0), but in Windows I have only Python3, the works goes smooth.

Kindly clarify my doubt and tell the right way to go about.

Answer 1

Try to run the following:

pip --version

Here is the output I get. Notice Python version mentioned within parenthesis.

pip 19.3.1 from /usr/local/lib/python3.5/dist-packages/pip (python 3.5)

To illustrate further, you have pip for Python 2.x and for Python 3.x. The following is output excerpts from apt-cache searches on my Ubuntu box:

python-pip - alternative Python package installer
python3-pip - alternative Python package installer - Python 3 version of the package

So, if you have installed both above you can run pip for Python 2.x and for Python 3.x:

pip2 --version
pip 19.3.1 from /usr/local/lib/python2.7/dist-packages/pip (python 2.7)

pip --version
pip 19.3.1 from /usr/local/lib/python3.5/dist-packages/pip (python 3.5)

Notice how pip on my box defaults to pip3 (the output in the last line is the same as the first output in the beginning of this answer.)

Hope this helps you.