How to set column headers to the first row in Pandas dataframe?

How do I set the column header of a dataframe to the first row of a dataframe and reset the column names?

# Creation of dataframe

df = pd.DataFrame({"A": ["1", "4", "7"],
                   "B": ["2", "5", "8"],
                   "C": ['3','6','9']})

# df:

   A  B  C
0  1  2  3
1  4  5  6
2  7  8  9

Desired Outcome:

   0  1  2
0  A  B  C
1  1  2  3
2  4  5  6
3  7  8  9

>Solution :

You can use np.vstack on a list of column names and the DataFrame to create an array with one extra row; then cast it into pd.DataFrame:

out = pd.DataFrame(np.vstack([df.columns, df]))

Output:

   0  1  2
0  A  B  C
1  1  2  3
2  4  5  6
3  7  8  9