def load_credentials(self, profile):
        f = profile_path(S3_PROFILE_ID, profile)
        if os.path.exists(f):
            creds = json.loads(base64.decodestring(open(f, 'rb').read()).encode('utf-8'))
            if 'access_key' not in creds:
                raise Exception("`access_key` not found in s3 profile '{0}'".format(profile))
            self.access_key = creds['access_key']
            if 'access_key' not in creds:
                raise Exception("`secret_key` not found in s3 profile '{0}'".format(profile))
            self.secret_key = creds['secret_key']
Loads crentials for a given profile. Profiles are stored in
dataset/ETHPy150Open yhat/db.py/db/db.py/S3.load_credentials