fix this code please:

def flatten$($L$)$:

$"""$Flattens list L recursively"""

if L $==[]$:

return $[]$

if L $!=[]$:

if isinstance$($L$[0],$ list$)$:

firstitem $=$ L$[0].$flatten$()$

else:

firstitem $=$ L$[$:$1]$

return firstitem $+$ flatten$($L$[1$:$])$