Exploring Alternatives to FindPython3 in CMake Projects

Purpose

• This enables your CMake project to interact with Python code during the build process.
• Locates the Python 3 interpreter, compiler (if applicable), and development environment (include directories and libraries).

Availability

• If you're using an older version, consider upgrading for broader Python 3 support.
• Introduced in CMake version 3.18.

Usage

1. find_package(Python3 COMPONENTS REQUIRED Interpreter Development)
   

   • REQUIRED: Ensures CMake halts if Python 3 cannot be found.
   • Interpreter: Finds the Python 3 interpreter (e.g., /usr/bin/python3).
   • Development: Locates development headers and libraries (necessary for linking Python modules).

2. Check for Success
   

   if(NOT Python3_FOUND)
       message(FATAL_ERROR "Python 3 not found")
   endif()
   

   • CMake sets Python3_FOUND to TRUE if successful, FALSE otherwise.

3. Access Variables
   

   message(STATUS "Python 3 interpreter: ${Python3_EXECUTABLE}")
   message(STATUS "Python 3 include directory: ${Python3_INCLUDE_DIRS}")
   message(STATUS "Python 3 libraries: ${Python3_LIBRARIES}")
   

   • CMake provides variables like Python3_EXECUTABLE, Python3_INCLUDE_DIRS, and Python3_LIBRARIES for linking and using Python modules in your project.

Additional Features

• Custom Search Paths
  

  set(PYTHON3_EXECUTABLE "/path/to/python3")
  find_package(Python3)
  

  • Override autodetection if Python 3 is in a non-standard location.

• Development Subcomponents (CMake 3.18+)
  

  find_package(Python3 COMPONENTS Development.Module)  # For module development
  find_package(Python3 COMPONENTS Development.Embed)    # For embedding Python in your project
  

  • Fine-tune your search for specific development needs.

• Version Specificity (CMake 3.19+)
  

  find_package(Python3 COMPONENTS Interpreter Development REQUIRED EXACT_VERSION 3.8)
  

  • Specifies a required exact Python version.
  • Use version ranges (<, <=, >=, >) for flexibility.

Incorporating into Your Project

• Access the provided variables for linking and using Python modules in your C++ code.
• Handle the success/failure case to ensure your project can build with Python 3.
• Include the FindPython3 module early in your CMakeLists.txt file.

---

Basic Integration

cmake_minimum_required(VERSION 3.18)
project(MyProject)

find_package(Python3 COMPONENTS REQUIRED Interpreter Development)

if(NOT Python3_FOUND)
    message(FATAL_ERROR "Python 3 not found")
endif()

# Link against Python libraries in your target
add_executable(my_executable main.cpp)
target_link_libraries(my_executable Python3::Python)

# Optionally use Python modules in your code
# (assuming you have a Python module named "my_module.py")
# include_directories(${Python3_INCLUDE_DIRS})

# ... rest of your CMakeLists.txt

This example first ensures CMake 3.18 or later for FindPython3 compatibility. It then finds Python 3's interpreter and development components, handling the case where Python 3 is not found. Finally, it links the my_executable target with Python libraries and provides an optional comment on including Python headers and using modules in your code.

Specifying Python Version (CMake 3.19+)

cmake_minimum_required(VERSION 3.19)
project(MyProject)

find_package(Python3 COMPONENTS Interpreter Development REQUIRED EXACT_VERSION 3.9)

# ... rest of your CMakeLists.txt

This example requires Python version 3.9 exactly.

Searching Custom Path

set(PYTHON3_EXECUTABLE "/custom/path/to/python3")
find_package(Python3)

# ... rest of your CMakeLists.txt

This example overrides the default search by setting the PYTHON3_EXECUTABLE variable to your custom Python 3 location.

Finding Specific Development Components

find_package(Python3 COMPONENTS Development.Module)  # For developing Python modules
# OR
find_package(Python3 COMPONENTS Development.Embed)    # For embedding Python

These examples search for specific development subcomponents based on your project's needs.

---

Manual Configuration

• If you have a simple setup and know the exact Python 3 installation paths, you can manually set the following variables in your CMakeLists.txt:
  • Python3_EXECUTABLE: Path to the Python 3 interpreter executable (e.g., /usr/bin/python3).
  • Python3_INCLUDE_DIRS: Path to the Python 3 include directory (e.g., /usr/include/python3.x).
  • Python3_LIBRARIES: Path to the Python 3 libraries (e.g., /usr/lib/libpython3.x.so).

Pros

• Fine-grained control over paths.
• Works with older CMake versions.

Cons

• Can be error-prone if you specify incorrect paths.
• Less portable and requires manual maintenance if Python 3 paths change.

Custom Find Module

• If you need more specific control beyond FindPython3 or have a unique setup, you can create a custom CMake module (FindMyPython3.cmake). This module would handle locating and setting Python 3 paths based on your logic.

Pros

• Highly customizable for specific needs.

Cons

• Might not be portable across different systems.
• Requires more effort to write and maintain the custom module.

Environment Variables

• In some cases, you can leverage environment variables like PYTHONPATH or PYTHON_LIBRARY to influence where CMake searches for Python 3. However, this approach can be less reliable and depends heavily on your system configuration.

Pros

• Can work in scenarios where CMake modules are not preferred.

Cons

• Not as portable as a proper CMake module.
• Environment variables might be overridden by other applications or scripts.