Set the current selection indent to the indent of the line above it with <C-Tab> in vim

vimrc

function! IndentAsPrevLine()
python << EOF
import itertools as I
from vim import *

if current.range.start > 0:

  def takewhile(pred,l): return ''.join(I.takewhile(pred,l))

  prev_line = current.buffer[current.range.start - 1]

  spaces = takewhile(lambda c:c.isspace(),prev_line)

  for idx in xrange(current.range.start,current.range.end+1):
    line = current.buffer[idx]
    curr_spaces = takewhile(lambda c:c.isspace(),line)
    
    # avoid multiple indent
    if len(spaces) != len(curr_spaces):
      current.buffer[idx] = spaces + line.lstrip()
EOF
endfunction

map <C-Tab> :call IndentAsPrevLine()<CR>