'Check namespace packages\' __init__ for declare_namespace'

def check_package(self, package, package_dir):

    try:
        return self.packages_checked[package]
    except KeyError:
        pass
    init_py = _build_py.check_package(self, package, package_dir)
    self.packages_checked[package] = init_py
    if ((not init_py) or (not self.distribution.namespace_packages)):
        return init_py
    for pkg in self.distribution.namespace_packages:
        if ((pkg == package) or pkg.startswith((package + '.'))):
            break
    else:
        return init_py
    f = open(init_py, 'rbU')
    if ('declare_namespace'.encode() not in f.read()):
        from distutils import log
        log.warn('WARNING:    %s    is    a    namespace    package,    but    its    __init__.py    does\nnot    declare_namespace();    setuptools    0.7    will    REQUIRE    this!\n(See    the    setuptools    manual    under    "Namespace    Packages"    for    details.)\n', package)
    f.close()
    return init_py
