<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def build_url_base(host, port, is_https):
 """ Make base of url based on config """

    base = "http"
    if is_https:
        base += 's'

    base += "://"
    base += host

    if port:
        base += ":"
        base += str(port)

    return base