OS X Keychain implementation in Python

keychain.py

class Keychain():
    """Reimplementation of Keyring for OS X.

       Problem with Keyring is it doesn't allow to set a label with is required
       for this use case.
    """

    class KeychainError(Exception):
        def __init__(self, code=None, msg=None, cause=None):
            self.code = code
            self.cause = cause
            if msg:
                self.msg = msg
            elif code == 44:
                self.msg = 'Keychain item not found'
            elif code == 51:
                self.msg = 'Keychain read permissions error'
            elif code == 195:
                self.msg='Keychain write permissions error'
            else:
                self.msg = 'Unknown Keychain error'

        def __str__(self):
            return repr(self.msg) + ' (' + repr(self.code) + '): ' + repr(self.cause)

    Login = '~/Library/Keychains/login.keychain'
    System = '/Library/Keychains/System.keychain'
    Default = None

    def __init__(self, keychain=None):
        self.keychain = keychain

    def get(self, **kwargs):
        cmd = ['/usr/bin/security', 'find-generic-password', '-w']
        if 'service' in kwargs:
            cmd += ['-s', kwargs['service']]
        if 'account' in kwargs:
            cmd += ['-a', kwargs['account']]
        if 'label' in kwargs:
            cmd += ['-l', kwargs['label']]
        if 'kind' in kwargs:
            cmd += ['-D', kwargs['kind']]
        if self.keychain:
            cmd += [self.keychain]

        logging.debug('$ %s', subprocess.list2cmdline(cmd))
        try:
            output = subprocess.check_output(cmd, shell=False, stderr=subprocess.STDOUT)
            return output.strip()
        except subprocess.CalledProcessError as e:
            raise Keychain.KeychainError(code=e.returncode, cause=e.output)

    def set(self, secret, **kwargs):
        cmd = ['/usr/bin/security', 'add-generic-password', '-w', secret, '-U']
        if 'service' in kwargs:
            cmd += ['-s', kwargs['service']]
        else:
            cmd += ['-s', self.lookup_service(**kwargs)]
        if 'account' in kwargs:
            cmd += ['-a', kwargs['account']]
        if 'label' in kwargs:
            cmd += ['-l', kwargs['label']]
        if 'kind' in kwargs:
            cmd += ['-D', kwargs['kind']]
        if self.keychain:
            cmd += [self.keychain]

        logging.debug('$ %s', subprocess.list2cmdline(cmd))
        try:
            subprocess.check_output(cmd, shell=False, stderr=subprocess.STDOUT)
        except subprocess.CalledProcessError as e:
            raise Keychain.KeychainError(code=e.returncode, cause=e.output)

    def lookup_service(self, **kwargs):
        cmd = ['/usr/bin/security', 'find-generic-password']
        if 'account' in kwargs:
            cmd += ['-a', kwargs['account']]
        if 'label' in kwargs:
            cmd += ['-l', kwargs['label']]
        if 'kind' in kwargs:
            cmd += ['-D', kwargs['kind']]
        if self.keychain:
            cmd += [self.keychain]

        logging.debug('$ %s', subprocess.list2cmdline(cmd))
	try:
            output = subprocess.check_output(cmd, shell=False, stderr=subprocess.STDOUT)
            for line in output.split():
                if '"svce"<blob>=' in line:
                    return line[14:-1]
        except subprocess.CalledProcessError as e:
            raise Keychain.KeychainError(code=e.returncode, cause=e.output)