from pandas.stats.api import ols
grps = df.groupby(['FID'])
for fid, grp in grps:
    result = ols(y=grp.loc[:, ('MEAN')], x=grp.loc[:, (['Accum_Prcp',
        'Accum_HDD'])])
text_file = open('Output {}.txt'.format(fid), 'w')
text_file.write(result.summary)
text_file.close()
Print OLS regression summary to text file