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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def plotres(psr,deleted=False,group=None,**kwargs):
 """Plot residuals, compute unweighted rms residual."""


    res, t, errs = psr.residuals(), psr.toas(), psr.toaerrs
    
    if (not deleted) and N.any(psr.deleted != 0):
        res, t, errs = res[psr.deleted == 0], t[psr.deleted == 0], errs[psr.deleted == 0]
        print("Plotting {0}/{1} nondeleted points.".format(len(res),psr.nobs))

    meanres = math.sqrt(N.mean(res**2)) / 1e-6
    
    if group is None:
        i = N.argsort(t)
        P.errorbar(t[i],res[i]/1e-6,yerr=errs[i],fmt='x',**kwargs)
    else:
        if (not deleted) and N.any(psr.deleted):
            flagmask = psr.flagvals(group)[~psr.deleted]
        else:
            flagmask = psr.flagvals(group)

        unique = list(set(flagmask))
            
        for flagval in unique:
            f = (flagmask == flagval)
            flagres, flagt, flagerrs = res[f], t[f], errs[f]
            i = N.argsort(flagt)
            P.errorbar(flagt[i],flagres[i]/1e-6,yerr=flagerrs[i],fmt='x',**kwargs)
        
        P.legend(unique,numpoints=1,bbox_to_anchor=(1.1,1.1))

    P.xlabel('MJD'); P.ylabel('res [us]')
    P.title("{0} - rms res = {1:.2f} us".format(psr.name,meanres))