Iterate through build_requires list and pip install if package is not present
    accounting for version

def install_build_requires(pkg_targets):
    """Iterate through build_requires list and pip install if package is not present
    accounting for version"""

    def pip_install(pkg_name, pkg_vers=None):
        pkg_name_version = '%s==%s' % (pkg_name, pkg_vers) if pkg_vers else pkg_name
        print '[WARNING] %s not found, attempting to install using a raw "pip install" call!' % pkg_name_version
        subprocess.Popen('pip install %s' % pkg_name_version, shell=True).communicate()

    def get_pkg_info(pkg):
        """Get package name and version given a build_requires element"""
        pkg_name, pkg_vers = None, None
        if '==' in pkg:
            pkg_name, pkg_vers = pkg.split('==')
        else:
            pkg_name = pkg.replace('>', '').replace('<', '').split('=')[0]
        return pkg_name, pkg_vers

    for pkg in pkg_targets:
        pkg_name, pkg_vers = get_pkg_info(pkg)
        try:
            pkg_name_version = '%s==%s' % (pkg_name, pkg_vers) if pkg_vers else pkg_name
            if pkg_vers:
                version = getattr(importlib.import_module(pkg_name), '__version__')
                if version != pkg_vers:
                    pip_install(pkg_name, pkg_vers)
            else:
                importlib.import_module(pkg_name)
        except ImportError:
            pip_install(pkg_name, pkg_vers)