Duplicate & switch case The goal is, having taken a string as input, duplicate each latin letter and "toggle" its case (i.e. uppercase becomes lowercase and vice-versa).

Example inputs &amp; outputs:

Input      Output
bad        bBaAdD
Nice       NniIcCeE
T e S t    Tt eE Ss tT
s E t      sS Ee tT
1!1!1st!   1!1!1sStT!
n00b       nN00bB     
(e.g.)     (eE.gG.)
H3l|@!     Hh3lL|@!


The input consists of printable ASCII symbols.

You shouldn't duplicate non-latin letters, numbers, special chars.
Python, 56 54 bytes



lambda s:''.join(c+c.swapcase()*c.isalpha()for c in s)


Test it on Ideone.