add multiple columns in dataframe python code example

Example 1: pandas merge two columns from different dataframes

#suppose you have two dataframes df1 and df2, and 
#you need to merge them along the column id
df_merge_col = pd.merge(df1, df2, on='id')

Example 2: add two column values of a datframe into one

df["period"] = df["Year"] + df["quarter"]