How to create a new dataframe column from existing columns using if-else

I have data frame and target value like this:

target = 'Math'

df:
Col1   Col2 
Math   Science
Music  Math
Social Math
Arts   Math

I want to create a new column(New_Col) such that 
if Col1 == target i.e Math:
    New_Col = Col2 value
else:
    New_Col = Col1 value

So the output looks like this:

df:

Col1   Col2        New_Col
Math   Science      Science
Music  Math         Music
Social Math         Social
Arts   Math         Arts

Can anyone help me with this?

>Solution :

My solution:

import pandas as pd

a = {'Col1':['Math', 'Music', 'Social','Arts'],  'Col2':['Science','Math', 'Math', 'Math']}
 
df = pd.DataFrame(a)
#if Col1 != Math: copy Col1
df['New_Col'] = df[df['Col1'] != 'Math' ]['Col1']
#if Col1 == Math: copy Col2
df.loc[df['New_Col'].isna(), 'New_Col'] = df[ df['Col1']== 'Math' ]['Col2']
df

Output:

     Col1     Col2  New_Col
0    Math  Science  Science
1   Music     Math    Music
2  Social     Math   Social
3    Arts     Math     Arts