Troubleshoot Vision-agents Installation With UV

Encountering issues when trying to install packages using uv, especially with complex dependencies like vision-agents, can be a common hurdle for developers. This article dives deep into a specific installation problem where uv add vision-agents fails, with a detailed look at the error messages and how to resolve them. We'll explore the underlying causes and provide actionable steps to get your vision-agents environment up and running smoothly.

Understanding the "Failed to build scipy" Error

One of the most common reasons for installation failures, particularly when dealing with scientific Python packages, is the inability of the build system to compile native code. This is precisely what happens when uv attempts to install vision-agents and encounters an error building the scipy package. The error message, Failed to build scipy==1.15.3, clearly indicates that the compilation process for this crucial scientific computing library has failed. Digging into the provided output, we see a critical line: ERROR: Unknown compiler(s): [['gfortran'], ['flang-new'], ['flang'], ['nvfortran'], ['pgfortran'], ['ifort'], ['ifx'], ['g95']]. This tells us that scipy, in its effort to build efficiently, relies on a Fortran compiler, and your system doesn't have one readily available or configured in a way that mesonpy (the build backend used here) can detect.

scipy is a fundamental package in the Python scientific ecosystem, providing modules for optimization, linear algebra, integration, interpolation, special functions, FFT, signal and image processing, ODE solvers, and other common tasks. Its robust performance often comes from highly optimized C, C++, and Fortran code. When you install scipy, especially from source (which happens when a pre-compiled binary wheel isn't available for your specific Python version and operating system), it needs to compile these underlying libraries. The build process, managed by mesonpy in this case, explicitly looks for Fortran compilers like gfortran (part of the GNU Compiler Collection) or other vendor-specific Fortran compilers. The absence of any of these compilers means meson cannot proceed with configuring the build, leading to the error you're seeing. The error message [Errno 2] No such file or directory: 'gfortran' confirms that the system couldn't find the executable for gfortran when it tried to check for its presence. This is a frequent issue on macOS and some Linux distributions if a full development toolchain, including Fortran support, isn't installed.

The Role of Build Tools and Dependencies

When installing Python packages, especially those with heavy numerical computation or system-level dependencies, it's crucial to understand that you're not just downloading Python code. Many packages, like scipy, rely on external libraries and require compilation tools to build their extensions. The uv package manager, while incredibly fast and efficient, still needs these underlying tools to be present on your system to successfully build packages from source. The scipy build process uses mesonpy, a build system that interfaces with meson. meson is a modern build system designed to be fast and user-friendly, but it still requires compilers and other development tools. The error log highlights that meson is specifically looking for a Fortran compiler. Fortran is a high-level programming language primarily used for scientific and engineering applications, and many core numerical routines in libraries like scipy are written in or interface with Fortran code for performance reasons. Without a Fortran compiler, scipy cannot be built.

Furthermore, the output mentions pkg-config is not found. pkg-config is a helper tool used during the compilation of native code. It provides information about installed libraries, such as the include paths and linker flags needed to compile and link against them. While the primary error here is the missing Fortran compiler, the absence of pkg-config could lead to further issues with other dependencies or even with scipy itself if it needs to link against other system libraries that are managed by pkg-config. Ensuring that pkg-config is installed and accessible in your system's PATH can prevent a cascade of build-related errors. The presence of clang (a C and C++ compiler) and cython is noted, which are essential, but they are not sufficient for building scipy when Fortran support is a requirement. The Python version detected (3.14) is also noted, which is unusual as Python versions typically go up to 3.12 or 3.13 in recent development cycles, suggesting a potential environment misconfiguration or a typo in the log interpretation, but the core issue remains the compilers.

Resolving the Fortran Compiler Issue for scipy

To overcome the scipy build failure, the primary solution is to ensure a suitable Fortran compiler is installed and discoverable by your system's build tools. The most common and recommended Fortran compiler for developers on Linux and macOS is gfortran, which is part of the GNU Compiler Collection (GCC). On macOS, you can install GCC, including gfortran, using the Homebrew package manager. If you don't have Homebrew installed, you can get it from brew.sh. Once Homebrew is set up, you can install GCC with the command brew install gcc. This command will install the latest version of GCC, which includes gfortran, and typically makes it available in your PATH.

After installing gcc via Homebrew, it's often necessary to ensure that your build system can find it. Homebrew installs compilers in a specific location (e.g., /usr/local/opt/gcc/bin or /opt/homebrew/opt/gcc/bin on Apple Silicon). You might need to configure your environment variables, such as PATH and CC, CXX, and FC (for Fortran compiler), to point to the Homebrew-installed compilers. However, mesonpy and other build tools are often smart enough to find compilers in standard Homebrew locations. A simpler approach, especially if you are using a Python environment manager like pyenv or conda, is to ensure that the Python interpreter itself is aware of these compilers. Sometimes, reinstalling the Python interpreter within your environment after installing gcc can help.

For users on Linux, gfortran is usually available through the system's package manager. For example, on Debian/Ubuntu systems, you would run sudo apt update && sudo apt install gfortran. On Fedora/CentOS/RHEL systems, you would use sudo dnf install gcc-gfortran or sudo yum install gcc-gfortran. Once installed, gfortran should be available in your system's PATH. If you are using conda, installing gcc or gfortran via conda (conda install gcc gxx gfortran) is often the most straightforward way to ensure compatibility within your conda environment.

In addition to gfortran, scipy's build process can also recognize other Fortran compilers like flang. If you have specific vendor compilers installed (e.g., Intel Fortran Compiler - ifort), meson might be able to detect those as well, provided they are correctly configured in your environment. The key is that one of the compilers listed in the scipy build requirements must be present and accessible. After installing the Fortran compiler, you should try running uv add vision-agents again. If scipy still fails to build, check the meson-log.txt file referenced in the error output for more detailed information about the build failure.

Addressing the av Build Failure with Missing Dependencies

When you attempt to install vision-agents with specific extras, such as `uv add