def METHOD_NAME(self):
    """
    Checks for the existence of an AWS credential file.
    If the environment variable AWS_CREDENTIAL_FILE is
    set and points to a file, that file will be read and
    will be searched credentials.
    Note that if credentials have been explicitelypassed
    into the class constructor, those values always take
    precedence.
    """
    if 'AWS_CREDENTIAL_FILE' in os.environ:
        path = os.environ['AWS_CREDENTIAL_FILE']
        path = os.path.expanduser(path)
        path = os.path.expandvars(path)
        if os.path.isfile(path):
            fp = open(path)
            lines = fp.readlines()
            fp.close()
            for line in lines:
                if line[0] != '#':
                    if '=' in line:
                        name, value = line.split('=', 1)
                        if name.strip() == 'AWSAccessKeyId':
                            if 'aws_access_key_id' not in self.args:
                                value = value.strip()
                                self.args['aws_access_key_id'] = value
                        elif name.strip() == 'AWSSecretKey':
                            if 'aws_secret_access_key' not in self.args:
                                value = value.strip()
                                self.args['aws_secret_access_key'] = value
        else:
            print('Warning: unable to read AWS_CREDENTIAL_FILE')