Array of Chars to String

[Michael Spencer]

Martin v. Löwis wrote:
> Apparently nobody has proposed this yet:
> >>>filter(letters.__contains__, astr)
> 'Bad'
> 
> >>>filter(set(letters).__contains__, astr)
> 'Bad'


Everyone is seeking early PEP 3000 compliance ;-)

filter wins on conciseness - it's short enought to use in-line, but for a fair 
speed comparison, I've wrapped it in a function, below; str.translate is far 
ahead on speed for all but the shortest strings:

def func_translate1(s, letters, table=string.maketrans("","")):
     return s.translate(table, table.translate(table, letters))

def func_filter1(s, letters):
     in_set = letters.__contains__
     return filter(in_set, s)

def func_filter2(s, letters):
     in_set = set(letters).__contains__
     return filter(in_set, s)


  >>> for m in (1, 10, 100, 1000, 10000):
  ...     s = "Bob Carol Ted Alice" * m
  ...     letters = "adB"
  ...     print "List length: %s" % len(s)
  ...     print shell.timefunc(func_translate1, s, letters)
  ...     print shell.timefunc(func_filter1, s, letters)
  ...     print shell.timefunc(func_filter2, s, letters)
  ...
  List length: 19
  func_translate1(...)  64179 iterations, 7.79usec per call
  func_filter1(...)  63706 iterations, 7.85usec per call
  func_filter2(...)  45336 iterations, 11.03usec per call
  List length: 190
  func_translate1(...)  54950 iterations, 9.10usec per call
  func_filter1(...)  12224 iterations, 40.90usec per call
  func_filter2(...)  10737 iterations, 46.57usec per call
  List length: 1900
  func_translate1(...)  22760 iterations, 21.97usec per call
  func_filter1(...)  1293 iterations, 386.87usec per call
  func_filter2(...)  1184 iterations, 422.52usec per call
  List length: 19000
  func_translate1(...)  3713 iterations, 134.67usec per call
  func_filter1(...)  137 iterations, 3.67msec per call
  func_filter2(...)  124 iterations, 4.05msec per call
  List length: 190000
  func_translate1(...)  426 iterations, 1.18msec per call
  func_filter1(...)  14 iterations, 38.29msec per call
  func_filter2(...)  13 iterations, 40.59msec per call
  >>>

Michael