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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 get_client_username(request: AxesHttpRequest, credentials: dict = None) -> str: """ Resolve client username from the given request or credentials if supplied. The order of preference for fetching the username is as follows: 1. If configured, use ``AXES_USERNAME_CALLABLE``, and supply ``request, credentials`` as arguments 2. If given, use ``credentials`` and fetch username from ``AXES_USERNAME_FORM_FIELD`` (defaults to ``username``) 3. Use request.POST and fetch username from ``AXES_USERNAME_FORM_FIELD`` (defaults to ``username``) :param request: incoming Django ``HttpRequest`` or similar object from authentication backend or other source :param credentials: incoming credentials ``dict`` or similar object from authentication backend or other source """


    if settings.AXES_USERNAME_CALLABLE:
        log.debug('Using settings.AXES_USERNAME_CALLABLE to get username')

        if callable(settings.AXES_USERNAME_CALLABLE):
            return settings.AXES_USERNAME_CALLABLE(request, credentials)
        if isinstance(settings.AXES_USERNAME_CALLABLE, str):
            return import_string(settings.AXES_USERNAME_CALLABLE)(request, credentials)
        raise TypeError('settings.AXES_USERNAME_CALLABLE needs to be a string, callable, or None.')

    if credentials:
        log.debug('Using parameter credentials to get username with key settings.AXES_USERNAME_FORM_FIELD')
        return credentials.get(settings.AXES_USERNAME_FORM_FIELD, None)

    log.debug('Using parameter request.POST to get username with key settings.AXES_USERNAME_FORM_FIELD')
    return request.POST.get(settings.AXES_USERNAME_FORM_FIELD, None)