class: center, middle .center[![Alt text](http://m1.paperblog.com/i/201/2016454/guia-python-conceptos-programacion-atributos--L-DTucOw.png)] # Python Course: Virtual Environment and Packages Shahid Beheshti University Instructor: S. M. Masoud Sadrnezhaad --- # Problem Python applications will often use packages and modules that don’t come as part of the standard library. Applications will sometimes need a specific version of a library, because the application may require that a particular bug has been fixed or the application may be written using an obsolete version of the library’s interface. This means it may not be possible for one Python installation to meet the requirements of every application. If application A needs version 1.0 of a particular module but application B needs version 2.0, then the requirements are in conflict and installing either version 1.0 or 2.0 will leave one application unable to run. --- # Solution The solution for this problem is to create a virtual environment, a self-contained directory tree that contains a Python installation for a particular version of Python, plus a number of additional packages. Different applications can then use different virtual environments. To resolve the earlier example of conflicting requirements, application A can have its own virtual environment with version 1.0 installed while application B has another virtual environment with version 2.0. If application B requires a library be upgraded to version 3.0, this will not affect application A’s environment. The module used to create and manage virtual environments is called venv. venv will usually install the most recent version of Python that you have available. If you have multiple versions of Python on your system, you can select a specific Python version by running python3 or whichever version you want. --- # Creating Virtual Environment To create a virtual environment, decide upon a directory where you want to place it, and run the venv module as a script with the directory path: ```bash python3 -m venv tutorial-env ``` This will create the tutorial-env directory if it doesn’t exist, and also create directories inside it containing a copy of the Python interpreter, the standard library, and various supporting files. --- # Activating the Virtual Environment Once you’ve created a virtual environment, you may activate it. On Windows, run: ```cmd tutorial-env\Scripts\activate.bat ``` On Unix or MacOS, run: ```bash source tutorial-env/bin/activate ``` (This script is written for the bash shell. If you use the csh or fish shells, there are alternate activate.csh and activate.fish scripts you should use instead.) --- # Activating the Virtual Environment (Contd) Activating the virtual environment will change your shell’s prompt to show what virtual environment you’re using, and modify the environment so that running python will get you that particular version and installation of Python. For example: ```bash $ source ~/envs/tutorial-env/bin/activate (tutorial-env) $ python Python 3.5.1 (default, May 6 2016, 10:59:36) ... >>> import sys >>> sys.path ['', '/usr/local/lib/python35.zip', ..., '~/envs/tutorial-env/lib/python3.5/site-packages'] >>> ``` --- # Installing the Python Package Managers ## Ubuntu ```bash sudo apt-get install python3-pip ``` ## MacOS ```bash sudo easy_install pip ``` ## Windows The official documentation tells users to install Pip and each of its dependencies from source. * Install setuptools
* Install pip
--- # Managing Packages with pip - Packages are **groups of functions** that someone else has built in Python **to share** with the world Packages can help you perform a set of functions - For example, the **requests** package lets you visit a webpage and retrieve the contents (source) as a string. - Before you can use someone else's package, you must install it onto your computer. Before you can install it on your computer, you'll need to install a package manager. - You can install, upgrade, and remove packages using a program called pip. By default pip will install packages from the Python Package Index,
. You can browse the Python Package Index by going to it in your web browser, or you can use pip’s limited search feature: - The preferred package manager is called pip. --- # Managing Packages with pip (Contd) ```bash (tutorial-env) $ pip search astronomy skyfield - Elegant astronomy for Python gary - Galactic astronomy and gravitational dynamics. novas - The United States Naval Observatory NOVAS astronomy library astroobs - Provides astronomy ephemeris to plan telescope observations PyAstronomy - A collection of astronomy related tools for Python. ... ``` pip has a number of subcommands: “search”, “install”, “uninstall”, “freeze”, etc. (Consult the Installing Python Modules guide for complete documentation for pip.) --- # Package Installation You can install the latest version of a package by specifying a package’s name: ```bash (tutorial-env) $ pip install novas Collecting novas Downloading novas-22.214.171.124.tar.gz (136kB) Installing collected packages: novas Running setup.py install for novas Successfully installed novas-126.96.36.199 ``` You can also install a specific version of a package by giving the package name followed by == and the version number: ```bash (tutorial-env) $ pip install requests==2.6.0 Collecting requests==2.6.0 Using cached requests-2.6.0-py2.py3-none-any.whl Installing collected packages: requests Successfully installed requests-2.6.0 ``` If you re-run this command, pip will notice that the requested version is already installed and do nothing. --- # Package Upgrade You can supply a different version number to get that version, or you can run pip install --upgrade to upgrade the package to the latest version: ```bash (tutorial-env) $ pip install --upgrade requests Collecting requests Installing collected packages: requests Found existing installation: requests 2.6.0 Uninstalling requests-2.6.0: Successfully uninstalled requests-2.6.0 Successfully installed requests-2.7.0 ``` pip uninstall followed by one or more package names will remove the packages from the virtual environment. --- # Installed packages pip show will display information about a particular package: ```bash (tutorial-env) $ pip show requests --- Metadata-Version: 2.0 Name: requests Version: 2.7.0 Summary: Python HTTP for Humans. Home-page: http://python-requests.org Author: Kenneth Reitz Author-email: email@example.com License: Apache 2.0 Location: /Users/akuchling/envs/tutorial-env/lib/python3.4/site-packages Requires: ``` pip list will display all of the packages installed in the virtual environment: ```bash (tutorial-env) $ pip list novas (188.8.131.52) numpy (1.9.2) pip (7.0.3) requests (2.7.0) setuptools (16.0) ``` --- # requirements.txt pip freeze will produce a similar list of the installed packages, but the output uses the format that pip install expects. A common convention is to put this list in a requirements.txt file: ```bash (tutorial-env) $ pip freeze > requirements.txt (tutorial-env) $ cat requirements.txt novas==184.108.40.206 numpy==1.9.2 requests==2.7.0 ``` The requirements.txt can then be committed to version control and shipped as part of an application. --- # requirements.txt (Contd) Users can then install all the necessary packages with install -r: ```bash (tutorial-env) $ pip install -r requirements.txt Collecting novas==220.127.116.11 (from -r requirements.txt (line 1)) ... Collecting numpy==1.9.2 (from -r requirements.txt (line 2)) ... Collecting requests==2.7.0 (from -r requirements.txt (line 3)) ... Installing collected packages: novas, numpy, requests Running setup.py install for novas Successfully installed novas-18.104.22.168 numpy-1.9.2 requests-2.7.0 ``` pip has many more options. Consult the Installing Python Modules guide for complete documentation for pip. When you’ve written a package and want to make it available on the Python Package Index, consult the Distributing Python Modules guide. --- class: center, middle # Let's see in action. Open your IDE. --- # References * https://docs.python.org/3/tutorial/venv.html --- class: center, middle .center[![Alt text](http://m1.paperblog.com/i/201/2016454/guia-python-conceptos-programacion-atributos--L-DTucOw.png)] # Thank you. Any questions?