<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _appendTrlFile(trlfile,drizfile):
 """ Append drizfile to already existing trlfile from CALXXX. """

    if not os.path.exists(drizfile):
        return
    # Open already existing CALWF3 trailer file for appending
    ftrl = open(trlfile,'a')
    # Open astrodrizzle trailer file
    fdriz = open(drizfile)

    # Read in drizzle comments
    _dlines = fdriz.readlines()

    # Append them to CALWF3 trailer file
    ftrl.writelines(_dlines)

    # Close all files
    ftrl.close()
    fdriz.close()

    # Now, clean up astrodrizzle trailer file
    os.remove(drizfile)