I want to append exactly one corresponding row from df_eng at the end of df12. df_eng & df12 have similar column size. I tried appending by df index (see my try in bold below), because len(Project_List) = len(df_eng). It can also be done by ‘Project’ row match I presume, but not sure how.

df_eng
Project Discipline
0 X1 AAA
1 X2 AAA
2 X3 AAA
3 X3 BBB
4 X3 CCC
…

df12
Project Discipline
0 X1 ZZZ
1 X2 ZZZ
2 X3 ZZZ
3 X4 ZZZ
4 X5 ZZZ
…

def X()
   ...
   a_pivot = pd.pivot_table(data_a,index=['Discipline'],values=['Hours'],aggfunc=np.sum)
   b_pivot = pd.pivot_table(data_b,index=['Discipline'],values=['Hours'],aggfunc=np.sum)
   dfa = a_pivot.reset_index()
   dfb = b_pivot.reset_index()
   df12 = pd.merge(dfa, dfb, how='left', on='Discipline')
   df12.insert(0, "Project", name, True)
   df12['Hours_x'] = df12['Hours_x'].fillna(0)
   df12['Hours_y'] = df12['Hours_y'].fillna(0)
   df12['Hours_x'] = df12['Hours_x'] - df12['Hours_y']

   **df12 = df12.append(df_eng.iloc[[i]], ignore_index=True)**

   ...
   df12.plot()
   pdf.savefig()
   pdf.close()
   ...

for i in Project_List:
    if i =='nan':
        continue
    try:
        X(df_eng, data_a, data_b, name = i)
    except:
        print('This project encountered an error - ' + str(i))

Anyone keen enough to help out a coding rookie? Thanks!