Replace part column value with value from another column of same dataframe
Your solution is close
Maybe just needed to add an apply.
Try:
df = pd.DataFrame({&quot;Name&quot;:[&quot;Name1&quot;, &quot;Name2&quot;, &quot;Name#DATE#&quot;], &quot;Date&quot;:[20200126, 20200127, 20200210]})

df[&quot;NewColumn&quot;] = df.apply(lambda row: row[&quot;Name&quot;].replace(&quot;#DATE#&quot;, str(row[&quot;Date&quot;])), axis = 1)

Outputs: