Pandas, Assign a value in a row, to another column based on a condition

[klllmmm]

I think I got it. Used a 2 pass approach - first pass to pick up the codes and values to be set in a dictionary. Second pass to set the values.

import pandas as pd
import numpy as np

df = pd.DataFrame(data = {'Code':[100,100,100,200,200],
                          'Value':[np.nan,1000,2000,np.nan,2000],
                          'ValueCount':[np.nan,1,2,np.nan,1],
                          'Expected_Cum_Value':[1000,1000,1000,2000,2000],})
df['Result_Value'] = ''
code_list = dict()
for row in df.itertuples() :
    if row.ValueCount == 1 :
        code_list[row.Code] = row.Value
for row_index in range(len(df)) :
    if df.iloc[row_index,0] in code_list:
        df.iloc[row_index,4] = code_list[df.iloc[row_index,0]]
df

Output:
	Code	Value	ValueCount	Expected_Cum_Value	Result_Value
0	100	NaN	NaN	1000	1000
1	100	1000.0	1.0	1000	1000
2	100	2000.0	2.0	1000	1000
3	200	NaN	NaN	2000	2000
4	200	2000.0	1.0	2000	2000

@jefsummers Thank you so much!!!