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Installing and using dynamic programming languages

Red Hat Enterprise Linux 9

A guide to installing and using dynamic programming languages in Red Hat Enterprise Linux 9

Red Hat Customer Content Services

Abstract

This document describes the basics of installing and using dynamic programming languages, such as Python and PHP on Red Hat Enterprise Linux 9.

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Chapter 1. Introduction to Python

Python is a high-level programming language that supports multiple programming paradigms, such as object-oriented, imperative, functional, and procedural paradigms. Python has dynamic semantics and can be used for general-purpose programming.

With Red Hat Enterprise Linux, many packages that are installed on the system, such as packages providing system tools, tools for data analysis, or web applications, are written in Python. To use these packages, you must have the python* packages installed.

1.1. Python versions

Python 3.9 is the default Python implementation in RHEL 9. Python 3.9 is distributed in a non-modular python3 RPM package in the BaseOS repository and usually installed by default. Python 3.9 will be supported for the whole life cycle of RHEL 9.

In the future, additional versions of Python 3 will be distributed as RPM packages with a shorter life cycle through the AppStream repository. These versions will be installable in parallel with Python 3.9.

Python 2 is not distributed with RHEL 9.

1.2. Major differences in the Python ecosystem since RHEL 8

This section summarizes major changes in the Python ecosystem in RHEL 9 compared to RHEL 8.

The unversioned python command

The unversioned form of the python command (/usr/bin/python) is available in the python-unversioned-command package. On some systems, this package is not installed by default. To install the unversioned form of the python command manually, use the dnf install /usr/bin/python command.

In RHEL 9, the unversioned form of the python command points to the default Python 3.9 version and it is an equivalent to the python3 and python3.9 commands.

The python command is intended for interactive sessions. In production, Red Hat recommends using python3 or python3.9 explicitly.

You can uninstall the unversioned python command by using the dnf remove /usr/bin/python command.

If you need a different python command, you can create custom symlinks in /usr/local/bin or ~/.local/bin or a Python virtual environment.

Several other unversioned commands are available, such as /usr/bin/pip in the python3-pip package. In RHEL 9, all unversioned commands point to the default Python 3.9 version.

Architecture-specific Python wheels

Architecture-specific Python wheels built on RHEL 9 newly adhere to the upstream architecture naming, which allows customers to build their Python wheels on RHEL 9 and install them on non-RHEL systems. Python wheels built on previous releases of RHEL are forward compatible and can be installed on RHEL 9. Note that this affects only wheels containing Python extensions, which are built for each architecture, not Python wheels with pure Python code, which is not architecture-specific.

Chapter 2. Installing and using Python

In RHEL 9, Python 3.9 is the default Python implementation. The unversioned python command points to the default Python 3.9 version.

2.1. Installing Python 3

The default Python implementation is usually installed by default. To install it manually, use the following procedure.

Procedure

  • To install Python, use:

    # dnf install python3

Verification steps

  • To verify the Python version installed on your system, use the following command:

    $ python3 --version

2.2. Installing additional Python 3 packages

Packages prefixed with python3 contain modules for the default Python 3.9 version.

Procedure

  • To install the Requests module for Python, use:

    # dnf install python3-requests
  • To install the pip package installer from Python, use:

    # dnf install python3-pip

2.3. Installing additional Python 3 tools for developers

Additional Python tools for developers are distributed through the CodeReady Linux Builder repository.

This repository contains, for example, the python3-pytest, python3-Cython packages and many others.

Important

The CodeReady Linux Builder repository and its content is unsupported by Red Hat.

To install packages from the repository, use the following the procedure.

Procedure

  1. Enable the CodeReady Linux Builder repository:

    # subscription-manager repos --enable codeready-builder-for-rhel-9-x86_64-rpms
  2. Install the python3-pytest package:

    # dnf install python3-pytest

2.4. Using Python

The following procedure contains examples of running the Python interpreter or Python-related commands.

Prerequisites

  • Ensure that Python is installed.

Procedure

  • To run the Python interpreter or related commands, use, for example:

    $ python3
    $ python3 -m pip --help
    $ python3 -m pip install package

Chapter 3. Packaging Python 3 RPMs

You can install Python packages on your system either from the upstream PyPI repository using the pip installer, or using the DNF package manager. DNF uses the RPM package format, which offers more downstream control over the software.

The packaging format of native Python packages is defined by Python Packaging Authority (PyPA) Specifications. Most Python projects use the distutils or setuptools utilities for packaging, and defined package information in the setup.py file. However, possibilities of creating native Python packages have evolved over time. For more information about emerging packaging standards, see pyproject-rpm-macros.

This chapter describes how to package a Python project that uses setup.py into an RPM package. This approach provides the following advantages compared to native Python packages:

  • Dependencies on Python and non-Python packages are possible and strictly enforced by the DNF package manager.
  • You can cryptographically sign the packages. With cryptographic signing, you can verify, integrate, and test content of RPM packages with the rest of the operating system.
  • You can execute tests during the build process.

3.1. SPEC file description for a Python package

A SPEC file contains instructions that the rpmbuild utility uses to build an RPM. The instructions are included in a series of sections. A SPEC file has two main parts in which the sections are defined:

  • Preamble (contains a series of metadata items that are used in the Body)
  • Body (contains the main part of the instructions)

An RPM SPEC file for Python projects has some specifics compared to non-Python RPM SPEC files.

Important

A name of any RPM package of a Python library must always include the python3- prefix.

Other specifics are shown in the following SPEC file example for the python3-pello package. For description of such specifics, see the notes below the example.

Name:           python-pello                                          1
Version:        1.0.2
Release:        1%{?dist}
Summary:        Example Python library

License:        MIT
URL:            https://github.com/fedora-python/Pello
Source:         %{url}/archive/v%{version}/Pello-%{version}.tar.gz

BuildArch:      noarch
BuildRequires:  python3-devel                                         2

# Build dependencies needed to be specified manually
BuildRequires:  python3-setuptools

# Test dependencies needed to be specified manually
# Also runtime dependencies need to be BuildRequired manually to run tests during build
BuildRequires:  python3-pytest >= 3


%global _description %{expand:
Pello is an example package with an executable that prints Hello World! on the command line.}

%description %_description

%package -n python3-pello                                             3
Summary:        %{summary}

%description -n python3-pello %_description


%prep
%autosetup -p1 -n Pello-%{version}


%build
# The macro only supported projects with setup.py
%py3_build                                                            4


%install
# The macro only supported projects with setup.py
%py3_install


%check                                                                5
%{pytest}


# Note that there is no %%files section for the unversioned python module
%files -n python3-pello
%doc README.md
%license LICENSE.txt
%{_bindir}/pello_greeting

# The library files needed to be listed manually
%{python3_sitelib}/pello/

# The metadata files needed to be listed manually
%{python3_sitelib}/Pello-*.egg-info/
1
When packaging a Python project into RPM, always add the python- prefix to the original name of the project. The original name here is pello and thus the name of the Source RPM (SRPM) is python-pello.
2
BuildRequires specifies what packages are required to build and test this package. In BuildRequires, always include items providing tools necessary for building Python packages: python3-devel and the relevant projects needed by the specific software you package, for example python3-setuptools or the runtime and testing dependencies needed to run the tests in the %check section.
3
When choosing a name for the binary RPM (the package that users will be able to install), add a versioned Python prefix, which is currently python3-. Therefore, the resulting binary RPM will be named python3-pello.
4
The %py3_build and %py3_install macros run the setup.py build and setup.py install commands, respectively, with additional arguments to specify installation locations, the interpreter to use, and other details.
5
The %check section should run the tests of the packaged project. The exact command depends very much on the project itself, but it is possible to use the %pytest macro to run the pytest command in an RPM-friendly way. The %{python3} macro contains a path for the Python 3 interpreter, that is, /usr/bin/python3. We recommend always using the macro rather than a literal path.

3.2. Common macros for Python 3 RPMs

In a SPEC file, always use the macros that are described in the following Macros for Python 3 RPMs table rather than hardcoding their values.

Table 3.1. Macros for Python 3 RPMs

MacroNormal DefinitionDescription

%{python3}

/usr/bin/python3

The Python 3 interpreter

%{python3_version}

3.9

The major.minor version of the Python 3 interpreter

%{python3_sitelib}

/usr/lib/python3.9/site-packages

The location where pure-Python modules are installed

%{python3_sitearch}

/usr/lib64/python3.9/site-packages

The location where modules containing architecture-specific extension modules are installed

%py3_build

 

Runs the setup.py build command with arguments suitable for an RPM package

%py3_install

 

Runs the setup.py install command with arguments suitable for an RPM package

%{py3_shebang_flags}

s

The default set of flags for the Python interpreter directives macro, %py3_shebang_fix

%py3_shebang_fix

 

Changes Python interpreter directives to #! %{python3}, preserves any existing flags (if found), and adds flags defined in the %{py3_shebang_flags} macro

3.3. Using automatically generated dependencies for Python RPMs

The following procedure describes how to use automatically generated dependencies when packaging a Python project as an RPM.

Prerequisites

Procedure

  1. Make sure that one of the following directories containing upstream-provided metadata is included in the resulting RPM:

    • .dist-info
    • .egg-info

      The RPM build process automatically generates virtual pythonX.Ydist provides from these directories, for example:

      python3.9dist(pello)

      The Python dependency generator then reads the upstream metadata and generates runtime requirements for each RPM package using the generated pythonX.Ydist virtual provides. For example, a generated requirements tag might look as follows:

      Requires: python3.9dist(requests)
  2. Inspect the generated requires.
  3. To remove some of the generated requires, use one of the following approaches:

    1. Modify the upstream-provided metadata in the %prep section of the SPEC file.
    2. Use automatic filtering of dependencies described in the upstream documentation.
  4. To disable the automatic dependency generator, include the %{?python_disable_dependency_generator} macro above the main package’s %description declaration.

Chapter 4. Handling interpreter directives in Python scripts

In Red Hat Enterprise Linux 9, executable Python scripts are expected to use interpreter directives (also known as hashbangs or shebangs) that explicitly specify at a minimum the major Python version. For example:

#!/usr/bin/python3
#!/usr/bin/python3.9

The /usr/lib/rpm/redhat/brp-mangle-shebangs buildroot policy (BRP) script is run automatically when building any RPM package, and attempts to correct interpreter directives in all executable files.

The BRP script generates errors when encountering a Python script with an ambiguous interpreter directive, such as:

#!/usr/bin/python

or

#!/usr/bin/env python

4.1. Modifying interpreter directives in Python scripts

Use the following procedure to modify interpreter directives in Python scripts that cause build errors at RPM build time.

Prerequisites

  • Some of the interpreter directives in your Python scripts cause a build error.

Procedure

  • To modify interpreter directives, complete one of the following tasks:

    • Use the following macro in the %prep section of your SPEC file:

      # %py3_shebang_fix SCRIPTNAME …​

      SCRIPTNAME can be any file, directory, or a list of files and directories.

      As a result, all listed files and all .py files in listed directories will have their interpreter directives modified to point to %{python3}. Existing flags from the original interpreter directive will be preserved and additional flags defined in the %{py3_shebang_flags} macro will be added. You can redefine the %{py3_shebang_flags} macro in your SPEC file to change the flags that will be added.

    • Apply the pathfix.py script from the python3-devel package:

      # pathfix.py -pn -i %{python3} PATH …​

      You can specify multiple paths. If a PATH is a directory, pathfix.py recursively scans for any Python scripts matching the pattern ^[a-zA-Z0-9_]+\.py$, not only those with an ambiguous interpreter directive. Add the command above to the %prep section or at the end of the %install section.

    • Modify the packaged Python scripts so that they conform to the expected format. For this purpose, you can use the pathfix.py script outside the RPM build process, too. When running pathfix.py outside an RPM build, replace %{python3} from the example above with a path for the interpreter directive, such as /usr/bin/python3.

Additional resources

Chapter 5. Using the PHP scripting language

Hypertext Preprocessor (PHP) is a general-purpose scripting language mainly used for server-side scripting, which enables you to run the PHP code using a web server.

5.1. Installing the PHP scripting language

This section describes how to install PHP.

Procedure

  • To install PHP, use:

    # dnf install php

5.2. Using the PHP scripting language with a web server

5.2.1. Using PHP with the Apache HTTP Server

In Red Hat Enterprise Linux 9, the Apache HTTP Server enables you to run PHP as a FastCGI process server. FastCGI Process Manager (FPM) is an alternative PHP FastCGI daemon that allows a website to manage high loads. PHP uses FastCGI Process Manager by default in RHEL 9.

This section describes how to run the PHP code using the FastCGI process server.

Prerequisites

  • The PHP scripting language is installed on your system.

Procedure

  1. Install the httpd package:

    # dnf install httpd
  2. Start the Apache HTTP Server:

    # systemctl start httpd

    Or, if the Apache HTTP Server is already running on your system, restart the httpd service after installing PHP:

    # systemctl restart httpd
  3. Start the php-fpm service:

    # systemctl start php-fpm
  4. Optional: Enable both services to start at boot time:

    # systemctl enable php-fpm httpd
  5. To obtain information about your PHP settings, create the index.php file with the following content in the /var/www/html/ directory:

    echo '<?php phpinfo(); ?>' > /var/www/html/index.php
  6. To run the index.php file, point the browser to:

    http://<hostname>/
  7. Optional: Adjust configuration if you have specific requirements:

    • /etc/httpd/conf/httpd.conf - generic httpd configuration
    • /etc/httpd/conf.d/php.conf - PHP-specific configuration for httpd
    • /usr/lib/systemd/system/httpd.service.d/php-fpm.conf - by default, the php-fpm service is started with httpd
    • /etc/php-fpm.conf - FPM main configuration
    • /etc/php-fpm.d/www.conf - default www pool configuration

Example 5.1. Running a "Hello, World!" PHP script using the Apache HTTP Server

  1. Create a hello directory for your project in the /var/www/html/ directory:

    # mkdir hello
  2. Create a hello.php file in the /var/www/html/hello/ directory with the following content:

    # <!DOCTYPE html>
    <html>
    <head>
    <title>Hello, World! Page</title>
    </head>
    <body>
    <?php
        echo 'Hello, World!';
    ?>
    </body>
    </html>
  3. Start the Apache HTTP Server:

    # systemctl start httpd
  4. To run the hello.php file, point the browser to:

    http://<hostname>/hello/hello.php

    As a result, a web page with the “Hello, World!” text is displayed.

5.2.2. Using PHP with the nginx web server

This section describes how to run PHP code through the nginx web server.

Prerequisites

  • The PHP scripting language is installed on your system.

Procedure

  1. Install the nginx package:

    # dnf install nginx
  2. Start the nginx server:

    # systemctl start nginx

    Or, if the nginx server is already running on your system, restart the nginx service after installing PHP:

    # systemctl restart nginx
  3. Start the php-fpm service:

    # systemctl start php-fpm
  4. Optional: Enable both services to start at boot time:

    # systemctl enable php-fpm nginx
  5. To obtain information about your PHP settings, create the index.php file with the following content in the /usr/share/nginx/html/ directory:

    echo '<?php phpinfo(); ?>' > /usr/share/nginx/html/index.php
  6. To run the index.php file, point the browser to:

    http://<hostname>/
  7. Optional: Adjust configuration if you have specific requirements:

    • /etc/nginx/nginx.conf - nginx main configuration
    • /etc/nginx/conf.d/php-fpm.conf - FPM configuration for nginx
    • /etc/php-fpm.conf - FPM main configuration
    • /etc/php-fpm.d/www.conf - default www pool configuration

Example 5.2. Running a "Hello, World!" PHP script using the nginx server

  1. Create a hello directory for your project in the /usr/share/nginx/html/ directory:

    # mkdir hello
  2. Create a hello.php file in the /usr/share/nginx/html/hello/ directory with the following content:

    # <!DOCTYPE html>
    <html>
    <head>
    <title>Hello, World! Page</title>
    </head>
    <body>
    <?php
        echo 'Hello, World!';
    ?>
    </body>
    </html>
  3. Start the nginx server:

    # systemctl start nginx
  4. To run the hello.php file, point the browser to:

    http://<hostname>/hello/hello.php

    As a result, a web page with the “Hello, World!” text is displayed.

Additional resources

5.3. Running a PHP script using the command-line interface

A PHP script is usually run using a web server, but also can be run using the command-line interface.

Prerequisites

  • The PHP scripting language is installed on your system.

Procedure

  1. In a text editor, create a filename.php file

    Replace filename with the name of your file.

  2. Execute the created filename.php file from the command line:

    # php filename.php

Example 5.3. Running a "Hello, World!" PHP script using the command-line interface

  1. Create a hello.php file with the following content using a text editor:

    <?php
        echo 'Hello, World!';
    ?>
  2. Execute the hello.php file from the command line:

    # php hello.php

    As a result, “Hello, World!” is printed.

5.4. Additional resources

  • httpd(8) — The manual page for the httpd service containing the complete list of its command-line options.
  • httpd.conf(5) — The manual page for httpd configuration, describing the structure and location of the httpd configuration files.
  • nginx(8) — The manual page for the nginx web server containing the complete list of its command-line options and list of signals.
  • php-fpm(8) — The manual page for PHP FPM describing the complete list of its command-line options and configuration files.

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