>>>jwt.decode(params, public_key, algorithm='RS256')
Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/jwt/api_jws.py", line 219, in _verify_signature
    alg_obj = self._algorithms[alg]
KeyError: 'RS256'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.5/dist-packages/jwt/api_jwt.py", line 92, in decode
    jwt, key=key, algorithms=algorithms, options=options, **kwargs
  File "/usr/local/lib/python3.5/dist-packages/jwt/api_jws.py", line 156, in decode
    key, algorithms)
  File "/usr/local/lib/python3.5/dist-packages/jwt/api_jws.py", line 226, in _verify_signature
    raise InvalidAlgorithmError('Algorithm not supported')
jwt.exceptions.InvalidAlgorithmError: Algorithm not supported

try:
    from cryptography.hazmat.primitives import hashes
    from cryptography.hazmat.primitives.serialization import (
        load_pem_private_key, load_pem_public_key, load_ssh_public_key
    )
    from cryptography.hazmat.primitives.asymmetric.rsa import (
        RSAPrivateKey, RSAPublicKey, RSAPrivateNumbers, RSAPublicNumbers,
        rsa_recover_prime_factors, rsa_crt_dmp1, rsa_crt_dmq1, rsa_crt_iqmp
    )
    from cryptography.hazmat.primitives.asymmetric.ec import (
        EllipticCurvePrivateKey, EllipticCurvePublicKey
    )
    from cryptography.hazmat.primitives.asymmetric import ec, padding
    from cryptography.hazmat.backends import default_backend
    from cryptography.exceptions import InvalidSignature

    has_crypto = True
except ImportError:
    has_crypto = False

requires_cryptography = set(['RS256', 'RS384', 'RS512', 'ES256', 'ES384',
                             'ES521', 'ES512', 'PS256', 'PS384', 'PS512'])


def get_default_algorithms():
    """
    Returns the algorithms that are implemented by the library.
    """
    default_algorithms = {
        'none': NoneAlgorithm(),
        'HS256': HMACAlgorithm(HMACAlgorithm.SHA256),
        'HS384': HMACAlgorithm(HMACAlgorithm.SHA384),
        'HS512': HMACAlgorithm(HMACAlgorithm.SHA512)
    }

    if has_crypto:
        default_algorithms.update({
            'RS256': RSAAlgorithm(RSAAlgorithm.SHA256),
            'RS384': RSAAlgorithm(RSAAlgorithm.SHA384),
            'RS512': RSAAlgorithm(RSAAlgorithm.SHA512),
            'ES256': ECAlgorithm(ECAlgorithm.SHA256),
            'ES384': ECAlgorithm(ECAlgorithm.SHA384),
            'ES521': ECAlgorithm(ECAlgorithm.SHA512),
            'ES512': ECAlgorithm(ECAlgorithm.SHA512),  # Backward compat for #219 fix
            'PS256': RSAPSSAlgorithm(RSAPSSAlgorithm.SHA256),
            'PS384': RSAPSSAlgorithm(RSAPSSAlgorithm.SHA384),
            'PS512': RSAPSSAlgorithm(RSAPSSAlgorithm.SHA512)
        })

    return default_algorithms