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string convert with python re
>>> line = "  abcn  defnn  ghin  jkl"
>>> print line
  abc
  def

  ghi
  jkl

>>> print "  abcdefnn  ghijkl"
  abcdef

  ghijkl

re.sub('(?P<word1>[^ns])ns*(?P<word2>[^ns])', 'g<word1>g<word2>', line)

>>> re.sub('(?P<word1>[^ns])ns*(?P<word2>[^ns])', 'g<word1>g<word2>', line)
Out: '  abcdefghijkl'

newline = re.sub(r"(?<!n)n[ t]*(?!n)", "", line)

(?<!n) # Assert that the previous character isn't a newline
n      # Match a newline
[ t]*  # Match any number of spaces/tabs
(?!n)  # Assert that the next character isn't a newline

>>> line = "  abcn  defnn  ghin  jkl"
>>> newline = re.sub(r"(?<!n)n[ t]*(?!n)", "", line)
>>> print newline
  abcdef

  ghijkl

line = "  abcn  defnn  ghin  jkl"
print re.sub(r'n(?!n)s*', '', line)

>>>  re.sub(r'([^n])n(?!n)s*', r'1', line)
'  abcdefnn  ghijkl'

>>> line = "  abcn  defnn  ghin  jkln"
>>> re.sub("([ ])|((?:[^n])n(?:[^n]))","",line)
'abdefnnghjkln'
>>>

>>> re.sub("([ t])|((?:[^n])n(?:[^n]))","",line)

>>> ''.join(x if 'nn' in x else x[:-1] for x in line.expandtabs(1).split(' ') if x != '')
'abcdefnnghijkl'

>>> import re
>>> line = "  abcn  defnn  ghin  jkl"
>>> print re.sub(r'(S+)ns*(S+)', r'12', line)
  abcdef

  ghijkl

>>> print re.sub(r'(?P<word1>[^ns]+)ns*(?P<word2>[^ns]+)', r'g<word1>g<word2>', line)
  abcdef

  ghijkl