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pykg-config 1.3.0

pkg-config replacement.

A pkg-config replacement.

pykg-config is an input- and output-compatible implementation of pkg-config written in Python for greater ease of portability. It is designed to be a drop-in replacement: command lines that work for pkg-config should produce identical output from pykg-config.

Requirements

pykg-config uses the new string formatting operations that were introduced in Python 2.6. It will not function with an earlier version of Python. It has been been tested with Python 2.6, 2.7, 3.1, 3.2, 3.3, and 3.4.

Installation

There are several methods of installation available:

1. Download the source (either from the repository or a source archive), extract it somewhere, and run pykg-config from that directory.

2. Download the source (either from the repository or a source archive), extract it somewhere, and use distutils to install it into your Python distribution:

  1. Extract the source, e.g. to a directory C:pykg-config

  2. Run setup.py to install pykg-config to your default Python installation:

    C:pykg-config> python setup.py install

  3. If necessary, set environment variables. These should be set by default, but if not you will need to set them yourself. On Windows, you will need to ensure that your Python site-packages directory is in the PYTHONPATH variable and the Python scripts directory is in the PATH variable. Typically, these will be something like C:Python26Libsite-packagesand C:Python26Scripts, respectively (assuming Python 2.6 installed in C:Python26).

3. Use the Windows installer. This will perform the same job as running setup.py (see #2), but saves opening a command prompt. You may still need to add paths to your environment variables

Under Unix-like operating systems, if you do not already have the original pkg-config available, you should create a symbolic link to pykg-config. This allows build system scripts that look for pkg-config to find pykg-config without modification. Place this link somewhere in your path. For example, assuming pykg-config was installed to /usr/local:

$ ln -s /usr/local/bin/pykg-config.py /usr/local/bin/pkg-config

On Windows, a batch file, pkg-config.bat, is installed along with pykg-config into the Scripts directory. This should function as a drop-in replacement for pkg-config in build system scripts, such as CMake’s UsePkgConfig.cmake module, provided that this directory is in your PATH environment variable.

Package paths

If a hard-coded package search path has been provided (see below), then only that path is searched for .pc files. Otherwise, paths are searched in this order:

  1. All paths listed in the PKG_CONFIG_PATH environment variable.
  2. All paths listed in the PKG_CONFIG_LIBDIR environment variable, if set. Otherwise, all paths in ${prefix}/lib[64]/pkgconfig/ and ${prefix}/share/pkgconfig/, where ${prefix} is a system prefix (typically this will be /usr/).
  3. On Windows, the registry keys HKEY_CURRENT_USERSoftwarepkg-configPKG_CONFIG_PATH and HKEY_LOCAL_MACHINESoftwarepkg-configPKG_CONFIG_PATH. For both of these, paths should be set as values of the key. The value name has no meaning to pkg-config; use it for your own reference. The value type must be REG_SZ (a string), and the data should be a single path.

If you are using Windows, I recommend you add paths to PKG_CONFIG_PATH. This is the easiest place to add paths to and the easiest to check for errors. Google can tell you how to add an environment variable in Windows. Unfortunately, because Windows does not have a centralised directory structure, you will probably have to add every package you install to this variable. If you are lucky, some nice packages will do it when they are installed, but I haven’t yet seen one that does this.

Hard-coded package path

It is possible, when installing using setup.py, to specify a hard-coded list of paths to be searched for .pc files. Use the following setup.py command to do so:

python setup.py build_py –with-pc-path=<desired paths here> install

The list of paths should be specified as a single string, with the paths separated by a semi-colon (‘;’) on Windows or a colon (‘:’) on other platforms.

pkg-config (.pc) file things-to-watch-out-for

The pkg-config format does not deal with spaces in values very well. If you have an include or lib path with a space in it (common on Windows), pkg-config will cheerfully treat up to the first space as an include or lib path, and then ignore all remaining words. This is despite correctly parsing the file with escaped spaces (the final value processing step is where it drops the rest).

By contrast, pykg-config uses Python’s shlex module to split values, preserving things like escaped spaces. This is an advantage on Windows (provided your .pc files properly escape their spaces), but does mean output is incompatible with pkg-config.

In the interest of user-friendliness, on Windows, full compatibility is _disabled_ by default (i.e. paths with escaped spaces are handled correctly). On other platforms, full compatibility is _enabled_ by default. You can manually turn it on or off using the –full-compatibility and –less-compatibility switches.

The standard Windows path format (using ) does not play well with some build systems, such as CMake. Fortunately, CMake correctly handles paths specified using Unix-style separators (/), so if your .pc files specify their paths using that format you shouldn’t have any problems.

Miscellaneous notes

  1. Default target compiler

The CMake pkg-config module does not handle Microsoft Visual C++ style libdir specifications (/libpath:). For this reason, even on Windows, the output defaults to the standard non-MSVC-compatible format. You can change which style is used with the –msvc-syntax and –no-msvc-syntax options.

  1. Testing compatibility

The test script, test_compatibility.py, performs a set of unit tests in an attempt to maintain compatibility with the version of pkg-config mentioned in CORRESPONDING_VERSION in pykg-config.py. Executing it will run through all the tests. If they all pass, pykg-config.py is producing the same output as the pkg-config installed on your system.

  1. Search prefix and system directories

pkg-config searchers in directories below a prefix that is defined at compile time. Typically, this prefix will be /usr/lib/ or /usr/lib64/, depending on the toolchain used to compile pkg-config. This path is then hard-coded into the binary and cannot be changed at run-time. The only way to change it is by recompiling pkg-config and forcing a different value for the system libpath onto it.

This presents a problem for pykg-config. Checking the Python system prefix (via sys.prefix) is not a guaranteed solution, as it is often different from the libpath used by the compiler that builds pkg-config. While not much of a problem for pykg-config’s main target (Windows), in order to ensure compatiblity it is best to try and meet this problem.

A nasty hack is used to try and fix this in the majority of cases. At startup, pykg-config looks at the value of sys.path. It finds the first entry containing ‘pythonxy.zip’ (where x and y are the major and minor version numbers). If the end of the containing directory name is ‘64’, it assumes that the system is running 64-bit libraries as the primary toolchain. This will cause paths such as /usr/lib/ (which are created from the sys.prefix value) to turn into /usr/lib64/.

You can test if the result is accurate for your system by ensuring that the ‘test_print_errors_with_error’ test will have an error caused by a package in /usr/lib64 (see the comments for that test), then running test_compatibility.py. If the error messages are the same (i.e. the test passes), then the hack has worked.

  1. Why?

Because building pkg-config for Windows in an easy-to-distribute, easy-to-use way is a pain. The core functionality of pkg-config is simple and easy to provide using Python (which provides several modules useful for such things as parsing text files, which is what .pc files are).

It was also fun.

 
File Type Py Version Uploaded on Size
pykg-config-1.3.0.macosx-10.9-intel.exe (md5) MS Windows installer any 2014-06-08 92KB
pykg-config-1.3.0.tar.gz (md5) Source 2014-06-08 23KB
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