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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def mod_repo(repo, **kwargs):
    '''
    Modify one or more values for a repo.  If the repo does not exist, it will
    be created, so long as uri is defined.

    The following options are available to modify a repo definition:

    repo
        alias by which opkg refers to the repo.
    uri
        the URI to the repo.
    compressed
        defines (True or False) if the index file is compressed
    enabled
        enable or disable (True or False) repository
        but do not remove if disabled.
    refresh
        enable or disable (True or False) auto-refresh of the repositories

    CLI Examples:

    .. code-block:: bash

        salt '*' pkg.mod_repo repo uri=http://new/uri
        salt '*' pkg.mod_repo repo enabled=False
    '''
    repos = list_repos()
    found = False
    uri = ''
    if 'uri' in kwargs:
        uri = kwargs['uri']

    for repository in repos:
        source = repos[repository][0]
        if source['name'] == repo:
            found = True
            repostr = ''
            if 'enabled' in kwargs and not kwargs['enabled']:
                repostr += '# '
            if 'compressed' in kwargs:
                repostr += 'src/gz ' if kwargs['compressed'] else 'src'
            else:
                repostr += 'src/gz' if source['compressed'] else 'src'
            repo_alias = kwargs['alias'] if 'alias' in kwargs else repo
            if ' ' in repo_alias:
                repostr += ' "{0}"'.format(repo_alias)
            else:
                repostr += ' {0}'.format(repo_alias)
            repostr += ' {0}'.format(kwargs['uri'] if 'uri' in kwargs else source['uri'])
            trusted = kwargs.get('trusted')
            repostr = _set_trusted_option_if_needed(repostr, trusted) if trusted is not None else \
                _set_trusted_option_if_needed(repostr, source.get('trusted'))
            _mod_repo_in_file(repo, repostr, source['file'])
        elif uri and source['uri'] == uri:
            raise CommandExecutionError(
                'Repository \'{0}\' already exists as \'{1}\'.'.format(uri, source['name']))

    if not found:
        # Need to add a new repo
        if 'uri' not in kwargs:
            raise CommandExecutionError(
                'Repository \'{0}\' not found and no URI passed to create one.'.format(repo))
        properties = {'uri': kwargs['uri']}
        # If compressed is not defined, assume True
        properties['compressed'] = kwargs['compressed'] if 'compressed' in kwargs else True
        # If enabled is not defined, assume True
        properties['enabled'] = kwargs['enabled'] if 'enabled' in kwargs else True
        properties['trusted'] = kwargs.get('trusted')
        _add_new_repo(repo, properties)

    if 'refresh' in kwargs:
        refresh_db()