Which paths does python ctypes module search for libraries on Mac OS?

Question

Python documentation (I checked both 2.7 and 3.4) states that:

On OS X, find_library() tries several predefined naming schemes and paths to locate the library, and returns a full pathname if successful:

Then gives examples coming from two folders: /usr/lib and /System/Library. I suppose this is not full list, as I have experience with python finding library from /usr/local/lib. What is the full list of paths python ctypes find_library searches on Mac OS X?

Answer 1

The function definition from the source lists the possible paths:

if os.name == "posix" and sys.platform == "darwin":
    from ctypes.macholib.dyld import dyld_find as _dyld_find
    def find_library(name):
        possible = ['lib%s.dylib' % name,
                    '%s.dylib' % name,
                    '%s.framework/%s' % (name, name)]
        for name in possible:
            try:
                return _dyld_find(name)
            except ValueError:
                continue
        return None

The relevant functions from macholib.dyld:

def dyld_env(env, var):
    if env is None:
        env = os.environ
    rval = env.get(var)
    if rval is None:
        return []
    return rval.split(':')
def dyld_image_suffix(env=None):
    if env is None:
        env = os.environ
    return env.get('DYLD_IMAGE_SUFFIX')

def dyld_framework_path(env=None):
    return dyld_env(env, 'DYLD_FRAMEWORK_PATH')

def dyld_library_path(env=None):
    return dyld_env(env, 'DYLD_LIBRARY_PATH')

def dyld_fallback_framework_path(env=None):
    return dyld_env(env, 'DYLD_FALLBACK_FRAMEWORK_PATH')

def dyld_fallback_library_path(env=None):
    return dyld_env(env, 'DYLD_FALLBACK_LIBRARY_PATH')


def dyld_image_suffix_search(iterator, env=None):
    """For a potential path iterator, add DYLD_IMAGE_SUFFIX semantics"""
    suffix = dyld_image_suffix(env)
    if suffix is None:
        return iterator
    def _inject(iterator=iterator, suffix=suffix):
        for path in iterator:
            if path.endswith('.dylib'):
                yield path[:-len('.dylib')] + suffix + '.dylib'
            else:
                yield path + suffix
            yield path
    return _inject()

def dyld_override_search(name, env=None):
    # If DYLD_FRAMEWORK_PATH is set and this dylib_name is a
    # framework name, use the first file that exists in the framework
    # path if any.  If there is none go on to search the DYLD_LIBRARY_PATH
    # if any.

    framework = framework_info(name)

    if framework is not None:
        for path in dyld_framework_path(env):
            yield os.path.join(path, framework['name'])

    # If DYLD_LIBRARY_PATH is set then use the first file that exists
    # in the path.  If none use the original name.
    for path in dyld_library_path(env):
        yield os.path.join(path, os.path.basename(name))

def dyld_executable_path_search(name, executable_path=None):
    # If we haven't done any searching and found a library and the
    # dylib_name starts with "@executable_path/" then construct the
    # library name.
    if name.startswith('@executable_path/') and executable_path is not None:
        yield os.path.join(executable_path, name[len('@executable_path/'):])

def dyld_find(name, executable_path=None, env=None):
    """
    Find a library or framework using dyld semantics
    """
    for path in dyld_image_suffix_search(chain(
                dyld_override_search(name, env),
                dyld_executable_path_search(name, executable_path),
                dyld_default_search(name, env),
            ), env):
        if os.path.isfile(path):
            return path
    raise ValueError("dylib %s could not be found" % (name,))

def dyld_default_search(name, env=None):
    yield name

    framework = framework_info(name)

    if framework is not None:
        fallback_framework_path = dyld_fallback_framework_path(env)
        for path in fallback_framework_path:
            yield os.path.join(path, framework['name'])

    fallback_library_path = dyld_fallback_library_path(env)
    for path in fallback_library_path:
        yield os.path.join(path, os.path.basename(name))

    if framework is not None and not fallback_framework_path:
        for path in DEFAULT_FRAMEWORK_FALLBACK:
            yield os.path.join(path, framework['name'])

    if not fallback_library_path:
        for path in DEFAULT_LIBRARY_FALLBACK:
            yield os.path.join(path, os.path.basename(name))

The defaults as per man dyld(1)

DEFAULT_FRAMEWORK_FALLBACK = [
    os.path.expanduser("~/Library/Frameworks"),
    "/Library/Frameworks",
    "/Network/Library/Frameworks",
    "/System/Library/Frameworks",
]

DEFAULT_LIBRARY_FALLBACK = [
    os.path.expanduser("~/lib"),
    "/usr/local/lib",
    "/lib",
    "/usr/lib",
]