'Get a list of user Resources that match the search string for assigning or creating issues.
This method is intended to find users that are eligible to create issues in a project or be assigned
to an existing issue. When searching for eligible creators, specify a project. When searching for eligible
assignees, specify an issue key.
:param username: a string to match usernames against
:param project: filter returned users by permission in this project (expected if a result will be used to
create an issue)
:param issueKey: filter returned users by this issue (expected if a result will be used to edit this issue)
:param expand: extra information to fetch inside each resource
:param startAt: index of the first user to return
:param maxResults: maximum number of users to return.
If maxResults evaluates as False, it will try to get all items in batches.'

def search_assignable_users_for_issues(self, username, project=None, issueKey=None, expand=None, startAt=0, maxResults=50):

    params = {u'username': username}
    if (project is not None):
        params[u'project'] = project
    if (issueKey is not None):
        params[u'issueKey'] = issueKey
    if (expand is not None):
        params[u'expand'] = expand
    return self._fetch_pages(User, None, u'user/assignable/search', startAt, maxResults, params)
