1. Python Virtual Environment and Package
In this blog, we will discuss what a Python virtual environment or Python Virtualenv is, and how to create one. We will also see how to install packages using pip. We talked about these in our tutorial on installing Python. If you still haven’t installed Python, do it right away.
2. Introduction to Python Virtualenv
Developing a Python application, you may want to use modules that don’t ship with the standard library. Or sometimes, you need a specific version of a library for a bug to be fixed, or for some other reason.
Does this mean that installing Python once isn’t enough for every application you craft? Maybe application X needs version 1.0, but application Y needs version 2.0. This leaves one of them unable to run.
To work with this, we create a virtual environment in Python. In essence, it is a self-contained directory tree containing a Python installation for a particular version of Python. Apart from that, it also has a list of additional packages. This way, application X can have its virtual environment with version 1.0, and B can have its own with version 2.0. Lets start with Create Python Virtual Environment.
3. Create a Virtual Environment in Python
To create virtualenv Python 3 and manage it, we use the module venv. Normally, it will install the latest version of Python for you, but you can choose that. But before we begin, let’s find out which version of Python we are using.
To do this, type the following in your Command Prompt (for Windows; type ‘cmd’ in search):
This is what it will look like:
Microsoft Windows [Version 10.0.16299.248]
(c) 2017 Microsoft Corporation. All rights reserved.
Now, let’s check if we have pip installed.
pip 9.0.1 from c:\users\lifei\appdata\local\programs\python\python36-32\lib\site-packages (python 3.6)
We do. This is because we installed Python from python.org. In case you do not have pip installed, you may need to install it manually.
Now, let’s begin. In your command prompt, move to the directory you want to work in:
Now, type in the following:
C:\Users\lifei\Desktop>python -m venv workwithenv
You will see the following directory on your Desktop (or whichever directory you chose to work with):
Inside this, you can see the following contents:
While the directory Include is empty, the other two aren’t:
As you can see, the command created the directory ‘workwithenv’ because it didn’t already exist. It also created subdirectories containing a copy of the Python interpreter, the standard library, and various supporting files.
Now, to activate the Python virtualenv, we will run the batch file activate.bat in the directory Scripts:
We get the following output:
This script is for the bash shell. If you have any doubt in Python virtualenv Python Virtual environment, Please comment. Before starting with Next topic you can read Python Packages Comprehensive Guide here.
4. Managing Python Packages with pip
Like we said earlier, pip is a program that will let you install, upgrade, and remove packages. Using pip, you can install packages from the Python Package Index (PyPI). Or, you can use pip’s search feature this way:
C:\Users\lifei\Desktop\workwithenv>pip search astronomy
acalib (0.1.3) – Advanced Computing for Astronomy Library
vaex-astro (0.1.5) – Astronomy related transformations and FITS file
astro-scripts (0.4.0) – Small scripts for astronomy
astrobase (0.3.8) – Python modules and scripts useful for variable star
work in astronomy.
astrocats (0.3.32) – Package for downloading, analyzing, and
constructing open astronomy catalogs.
astrodbkit (0.6.6) – Astronomy database management using SQL and Python
astroML (0.3) – tools for machine learning and data mining in
astromodels (0.4.1) – Astromodels contains models to be used in
likelihood or Bayesian analysis in astronomy
astroobs (1.4.5) – Provides astronomy ephemeris to plan telescope
astropy (3.0) – Community-developed python astronomy tools
astropyp (0.0.dev133) – Astronomy Pypeline Framework and FITS Viewer
astrotoyz (0.1.4) – Astronomy tools built on the Toyz framework
Barak (0.3.2) – A set of astronomy-related routines for generating
Voigt profiles from atomic data, reading and
writing data, working with SEDs, passbands and dust
cadcdata (1.2.1) – Client for accessing data at the Canadian Astronomy
python-casacore (2.2.1) – A wrapper around CASACORE, the radio astronomy
cygrid (0.9.8) – Cygrid is a cython-powered convolution-based
gridding module for astronomy
DDFacet (0.3.2) – Facet-based radio astronomy continuum imager
f311 (188.8.131.52) – Astronomy-related API, command-line tools, and
gammapy (0.7) – A Python package for gamma-ray astronomy
gary (0.1a) – Galactic astronomy and gravitational dynamics.
gastropy (0.0dev) – (g)astronomy
hips (0.2) – Python astronomy package for HiPS
mclearn (0.1.6) – Active learning algorithms with application in
novas (184.108.40.206) – The United States Naval Observatory NOVAS astronomy
palpy (1.8.1) – PAL — A Positional Astronomy Library
PyAstronomy (0.12.0) – A collection of astronomy related tools for Python.
pyzpace (0.2.dev1) – Zach Pace’s astronomy-related python tools
sinistra (0.3.3) – A collection of astronomy related tools.
skyfield (1.1) – Elegant astronomy for Python
SWHT (0.1.2) – Spherical Wave Harmonic Transform for radio
astronomy visibility data
This listed out a list of packages that work with astronomy. Now, we want to search for packages working with numbers. (We won’t include the output since it’s too long to include here) But I have a feeling we want to work with the package ‘numpy’ here. Let’s install it. I also recommend you to read Python Modules vs Packages for better understanding.
a. Installing Python packages
C:\Users\lifei\Desktop\workwithenv>pip install numpy
Using cached numpy-1.14.1-cp36-none-win32.whl
Installing collected packages: numpy
Successfully installed numpy-1.14.1
This is what it looks like in the command prompt:
Now, we look into C:\Users\lifei\AppData\Local\Programs\Python\Python36-32\Lib\site-packages, and we find this:
Actually, pip has a number of subcommands like search, install, uninstall, and freeze.
You can also install a specific version of a package by following the package name by ==, and then by the version number:
pip install numpy==1.14.1
In fact, to check what version of numpy you are using, you can type the following in the interpreter:
>>> import numpy
Or, you can do:
Running the command to install numpy again will just be ignored by the interpreter.
C:\Users\lifei\Desktop\workwithenv>pip install numpy
Requirement already satisfied: numpy in c:\users\lifei\appdata\local\programs\python\python36-32\lib\site-packages
You may also want to Read about Python Dictionary with Methods, Functions and Dictionary Operations
b. Checking for Upgrades
However, you can check for upgrades:
C:\Users\lifei\Desktop\workwithenv>pip install –upgrade numpy
Requirement already up-to-date: numpy in c:\users\lifei\appdata\local\programs\python\python36-32\lib\site-packages
c. Uninstalling a Python Package
To uninstall a package, we do this:
C:\Users\lifei\Desktop\workwithenv>pip uninstall certifi
Proceed (y/n)? y
Successfully uninstalled certifi-2018.1.18
d. Learning About a Python Package
To find out about a particular package, we use the subcommand ‘show’:
C:\Users\lifei\Desktop\workwithenv>pip show numpy
Summary: NumPy: array processing for numbers, strings, records, and objects.
Author: NumPy Developers
e. To List the Packages Installed in Python
Now, to list all packages that are installed, we use ‘list’:
DEPRECATION: The default format will switch to columns in the future. You can use –format=(legacy|columns) (or define a format=(legacy|columns) in your pip.conf under the [list] section) to disable this warning.
This listed the packages alongside the versions installed.
The freeze subcommand with pip will return a list of packages installed, but in the format that pip install expects:
This is all about Python Virtual Environment and Packages in Python.
Read my article on The Tremendous Python Career Opportunities in 2018
In this lesson on Python virtual environment or Python Virtualenv and Python Packages we learned about how to set up a virtual environment so all your applications will run without a dispute. Then, we learned how to use pip to install a package. We also saw subcommands like show, list, freeze, and so. Hope You like the tutorial on Python virtual environment and Packages.