pyopenssl.py 文件源码

def _validate_dependencies_met():
    """
    Verifies that PyOpenSSL's package-level dependencies have been met.
    Throws `ImportError` if they are not met.
    """
    # Method added in `cryptography==1.1`; not available in older versions
    from cryptography.x509.extensions import Extensions
    if getattr(Extensions, "get_extension_for_class", None) is None:
        raise ImportError("'cryptography' module missing required functionality.  "
                          "Try upgrading to v1.3.4 or newer.")

    # pyOpenSSL 0.14 and above use cryptography for OpenSSL bindings. The _x509
    # attribute is only present on those versions.
    from OpenSSL.crypto import X509
    x509 = X509()
    if getattr(x509, "_x509", None) is None:
        raise ImportError("'pyOpenSSL' module missing required functionality. "
                          "Try upgrading to v0.14 or newer.")