<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def git_str(self):
 """ If the distribution is not installed via git, return an empty string. If the distribution is installed via git and pip recognizes the git source, return the pip requirement string specifying the git URL and commit, with an '*' appended if :py:attr:`~.git_is_dirty` is True. Otherwise, return a string of the form: url@ref[*] Where URL is the remote URL, ref is the tag name if the repo is checked out to a commit that matches a tag or else the commit hex SHA, and '*' is appended if :py:attr:`~.git_is_dirty` is True. :return: description of the git repo remote and state :rtype: str """

        dirty = '*' if self._git_is_dirty else ''
        if 'git' in self._pip_requirement:
            return self._pip_requirement + dirty
        if self._git_commit is None and self._git_remotes is None:
            return ''
        ref = self._git_tag if self._git_tag is not None else self._git_commit
        return '%s@%s%s' % (self.git_remote, ref, dirty)