How can I duplicate a row and append it directly after the duplicated row using pandas?

Question

I've been trying to figure this problem for a couple of hours now and seem to reach a dead end everytime. A small example of what I want to do is shown below.

Normal Series
a
b
c
d

Duplicated Series
a
a
b
b
c
c
d
d

Answer 1

Try with loc and df.index.repeat:

>>> df.loc[df.index.repeat(2)]
  Normal Series
0             a
0             a
1             b
1             b
2             c
2             c
3             d
3             d
>>> 

Or with reset_index:

>>> df.loc[df.index.repeat(2)].reset_index(drop=True)
  Normal Series
0             a
1             a
2             b
3             b
4             c
5             c
6             d
7             d
>>>