<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def urijoin(base, ref, strict=False):
 """Convert a URI reference relative to a base URI to its target URI string. """

    if isinstance(base, type(ref)):
        return urisplit(base).transform(ref, strict).geturi()
    elif isinstance(base, bytes):
        return urisplit(base.decode()).transform(ref, strict).geturi()
    else:
        return urisplit(base).transform(ref.decode(), strict).geturi()