Python - Environment Setup

First step in the journey of learning Python is to install it on your machine. Today most computer machines, especially having Linux OS, have Python pre-installed. However, it may not be the latest version.

In this section, we shall learn to install the latest version of Python, Python 3.11.2, on Linux, Windows and Mac OS.

Latest version of Python for all the operating system environments can be downloaded from PSF’s official website.

Install Python on Ubuntu Linux

To check whether Python is already installed, open the Linux terminal and enter the following command −

user@ubuntu20:~$ python3 --version

In Ubuntu Linux, the easiest way to install Python is to use apt – Advanced Packaging Tool. It is always recommended to update the list of packages in all the configured repositories.

user@ubuntu20:~$ sudo apt update

Even after the update, the latest version of Python may not be available for install, depending upon the version of Ubuntu you are using. To overcome this, add the deadsnakes repository.

user@ubuntu20:~$ sudo apt-get install software-properties-common
user@ubuntu20:~$ sudo add-apt-repository ppa:deadsnakes/ppa

Update the package list again.

user@ubuntu20:~$ sudo apt update

To install the latest Python 3.11 version, enter the following command in the terminal −

user@ubuntu20:~$ sudo apt-get install python3.11

Check whether it has been properly installed.

user@ubuntu20:~$ python3.11
Python 3.11.2 (main, Feb 8 2023, 14:49:24) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print ("Hello World")
Hello World
>>>

Install Python on Windows

It may be noted that Python’s version 3.10 onwards cannot be installed on Windows 7 or earlier operating systems.

The recommended way to install Python is to use the official installer. Linn to the latest stable version is given on the home page itself. It is also found at https://www.python.org/downloads/windows/.

You can find embeddable packages and installers for 32 as well as 64-bit architecture.

Let us download 64-bit Windows installer −

(https://www.python.org/ftp/python/3.11.2/python-3.11.2-amd64.exe)

Double click on the file where it has been downloaded to start the installation.

Although you can straight away proceed by clicking the Install Now button, it is advised to choose the installation folder with a relatively shorter path, and tick the second check box to update the PATH variable.

Accept defaults for rest of the steps in this installation wizard to complete the installation.

Open the Window Command Prompt terminal and run Python to check the success of installation.

C:\Users\Acer>python
Python 3.11.2 (tags/v3.11.2:878ead1, Feb 7 2023, 16:38:35) [MSC v.1934
64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>

Python’s standard library has an executable module called IDLE – short for Integrated Development and Learning Environment. Find it from Window start menu and launch.

IDLE contains Python shell (interactive interpreter) and a customizable multi-window text editor with features such as syntax highlighting, smart indent, auto completion etc. It is cross-platform so works the same on Windows, MacOS and Linux. It also has a debugger with provision to set breakpoints, stepping, and viewing of global and local namespaces.

Install Python on MacOS

Earlier versions of MacOS used to have Python 2.7 pre-installed in it. However, now that the version no longer supported, it has been discontinued. Hence, you need to install Python on your own.

On a Mac computer, Python can be installed by two methods −

• Using the official installer

• Manual installation with homebrew

You can find macOS 64-bit universal2 installer on the downloads page of the official website −

https://www.python.org/ftp/python/3.11.2/python-3.11.2-macos11.pkg

The installation process is more or less similar to that on Windows. Usually, accepting the default options during the wizard steps should do the work.

The frequently required utilities such as PIP and IDLE are also installed by this installation wizard.

Alternately, you can opt for the installation from command line. You need to install Homebrew, Mac’s package manager, if it is not already available. You can follow the instructions for installation at https://docs.brew.sh/Installation.

After that, open the terminal and enter the following commands −

brew update && brew upgrade
brew install python3

Latest version of Python will now be installed.

Install Python from Source Code

If you are an experienced developer, with good knowledge of C++ and Git tool, you can follow the instructions in this section to build Python executable along with the modules in the standard library.

You must have the C compiler for the OS that you are on. In Ubuntu and MacOS, gcc compiler is available. For Windows, you should install Visual Studio 2017 or later.

Steps to Build Python on Linux/Mac

Download the source code of Python’s latest version either from Python’s official website or its GitHub repository.

Extract the files with the command −

tar -xvzf /home/python/Python-3.11.2.tgz

Alternately, clone the main branch of Python’s GitHub repository. (You should have git installed)

git clone -b main https://github.com/python/cpython

A configure script comes in the source code. Running this script will create the makefile.

./configure --enable-optimizations

Followed by this, use the make tool to build the files and then make install to put the final files in /usr/bin/ directory.

make
make install

Python has been successfully built from the source code.

If you use Windows, make sure you have Visual Studio 2017 and Git for Windows installed. Clone the Python source code repository by the same command as above.

Open the windows command prompt in the folder where the source code is placed. Run the following batch file

PCbuild\get_externals.bat

This downloads the source code dependencies (OpenSSL, Tk etc.)

Open Visual Studio and PCbuild/sbuild.sln solution, and build (press F10) the debug folder shows python_d.exe which is the debug version of Python executable.

To build from command prompt, use the following command −

PCbuild\build.bat -e -d -p x64

Thus, in this chapter, you learned how to install Python from the pre-built binaries as well as from the source code.

Setting Up the PATH

When the Python software is installed, it should be accessible from anywhere in the file system. For this purpose, the PATH environment variable needs to be updated. A system PATH is a string consisting of folder names separated by semicolon (;). Whenever an executable program is invoked from the command line, the operating system searches for it in the folders listed in the PATH variable. We need to append Python’s installation folder to the PATH string.

In case of Winows operating system, if you have enabled “add python.exe to system path” option on the first screen of the installation wizard, the path will be automatically updated. To do it manually, open Environment Variables section from Advanced System Settings.

Edit the Path variable, and add a new entry. Enter the name of the installation folder in which Python has been installed, and press OK.

To add the Python directory to the path for a particular session in Linux −

In the bash shell (Linux) − type export PATH="$PATH:/usr/bin/python3.11" and press Enter.

Python Command Line Options

We know that interactive Python interpreter can be invoked from the terminal simply by calling Python executable. Note that no additional parameters or options are needed to start the interactive session.

user@ubuntu20:~$ python3.11
Python 3.11.2 (main, Feb 8 2023, 14:49:24) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print ("Hello World")
Hello World
>>>

Python interpreter also responds to the following command line options −

-c <command>

Interpreters execute one or more statements in a string, separated by newlines (;) symbol.

user@ubuntu20:~$ python3 -c "a=2;b=3;print(a+b)"
5

-m <module-name>

Interpreter executes the contents of named module as the __main__ module. Since the argument is a module name, you must not give a file extension (.py).

Consider the following example. Here, the timeit module in standard library has a command line interface. The -s option sets up the arguments for the module.

C:\Users\Acer>python -m timeit -s "text = 'sample string'; char = 'g'
'char in text'"
5000000 loops, best of 5: 49.4 nsec per loop

<script>

Interpreter executes the Python code contained in script with .py extension, which must be a filesystem path (absolute or relative).

Assuming that a text file with the name hello.py contains print (“Hello World”) statement is present in the current directory. The following command line usage of script option.

C:\Users\Acer>python hello.py
Hello World

? Or -h or –help

This command line option prints a short description of all command line options and corresponding environment variables and exit.

-V or --version

This command line option prints the Python version number

C:\Users\Acer>python -V
Python 3.11.2
C:\Users\Acer>python --version
Python 3.11.2

Python Environment Variables

The operating system uses path environment variable to search for any executable (not only Python executable). Python specific environment variables allow you to configure the behaviour of Python. For example, which folder locations to check to import a module. Normally Python interpreter searches for the module in the current folder. You can set one or more alternate folder locations.

Python environment variables may be set temporarily for the current session or may be persistently added in the System Properties as in case of path variable.

PYTHONPATH

As mentioned above, if you want the interpreter should search for a module in other folders in addition to the current, one or more such folder locations are stored as PYTHONPATH variable.

First, save hello.py script in a folder different from Python’s installation folder, let us say c:\modulepath\hello.py

To make the module available to the interpreter globally, set PYTHONPATH

C:\Users\Acer>set PYTHONPATH= c:\modulepath
C:\Users\Acer>echo %PYTHONPATH%
c:\modulepath

Now you can import the module even from any directory other than c:\modulepath directory.

>>> import hello
Hello World
>>>

PYTHONHOME

Set this variable to change the location of the standard Python libraries. By default, the libraries are searched in /usr/local/pythonversion in case of Linux and instalfolder\lib in Windows. For example, c:\python311\lib.

PYTHONSTARTUP

Usually, this variable is set to a Python script, which you intend to get automatically executed every time Python interpreter starts.

Let us create a simple script as follows and save it as startup.py in the Python installation folder −

print ("Example of Start up file")
print ("Hello World")

Now set the PYTHONSTARTUP variable and assign name of this file to it. After that start the Python interpreter. It shows the output of this script before you get the prompt.

F:\311_2>set PYTHONSTARTUP=startup.py
F:\311_2>echo %PYTHONSTARTUP%
startup.py
F:\311_2>python
Python 3.11.2 (tags/v3.11.2:878ead1, Feb 7 2023, 16:38:35) [MSC v.1934
64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
Example of Start up file
Hello World
>>>

PYTHONCASEOK

This environment is available for use only on Windows and MacOSX, not on Linux. It causes Python to ignore the cases in import statement.

PYTHONVERBOSE

If this variable is set to a non-empty string it is equivalent to specifying python -v command. It results in printing a message, showing the place (filename or built-in module) each time a module is initialized. If set to an integer – say 2, it is equivalent to specifying -v two times. (python --v).

PYTHONDONTWRITEBYTECODE

Normally, the imported modules are compiled to .pyc file. If this variable is set to a not null string,the .pyc files on the import of source modules are not created.

PYTHONWARNINGS

Python’s warning messages are redirected to the standard error stream, sys.stderr. This environment variable is equivalent to the python -W option. The following are allowed values of this variable −

• PYTHONWARNINGS=default # Warn once per call location

• PYTHONWARNINGS=error # Convert to exceptions

• PYTHONWARNINGS=always # Warn every time

• PYTHONWARNINGS=module # Warn once per calling module

• PYTHONWARNINGS=once # Warn once per Python process

• PYTHONWARNINGS=ignore # Never warn