<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def lon_to_deg(lon):
 """Convert longitude to degrees."""

    if isinstance(lon, str) and (':' in lon):
        # TODO: handle other coordinate systems
        lon_deg = hmsStrToDeg(lon)
    else:
        lon_deg = float(lon)
    return lon_deg