<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_expstart(header,primary_hdr):
 """shouldn't this just be defined in the instrument subclass of imageobject?"""


    if 'expstart' in primary_hdr:
        exphdr = primary_hdr
    else:
        exphdr = header

    if 'EXPSTART' in exphdr:
        expstart = float(exphdr['EXPSTART'])
        expend = float(exphdr['EXPEND'])
    else:
        expstart = 0.
        expend = 0.0

    return (expstart,expend)