Revision 11 as of 2005-09-03 02:27:14

Clear message

This page discusses the benefits of replacing the current print statement with an equivalent builtin. The output function presented below does everything the print statement does without requiring any hacking of the grammar, and also makes a number of things significantly easier.

Benefits of using a function instead of a statement

Sample implementation

This is a Python 2.4 compatible sample implementation, which is why it uses the name output rather than print. Try not to get too hung up on names at this stage :)

   1 def output(*args, **kwds):
   2     """Functional replacement for the print statement
   3 
   4     >>> output(1, 2, 3)
   5     1 2 3
   6     >>> output(1, 2, 3, sep='')
   7     123
   8     >>> output(1, 2, 3, sep=', ')
   9     1, 2, 3
  10     >>> output(1, 2, 3, term='Alternate line terminator')
  11     1 2 3Alternate line terminator
  12     >>> import sys
  13     >>> output(1, 2, 3, stream=sys.stderr)
  14     1 2 3
  15     >>> output(*range(10))
  16     0 1 2 3 4 5 6 7 8 9
  17     >>> output(*(x*x for x in range(10)))
  18     0 1 4 9 16 25 36 49 64 81
  19     """
  20     # Parse the keyword-only optional arguments
  21     defaults = {
  22         "sep": " ",
  23         "term": "\n",
  24         "stream": sys.stdout,
  25     }
  26     for name, default in defaults.items():
  27         item = None
  28         try:
  29             item = kwds[name]
  30         except KeyError:
  31             pass
  32         if item is None:
  33             kwds[name] = default
  34     sep, term, stream = kwds["sep"], kwds["term"], kwds["stream"]
  35     # Perform the print operation without building the whole string
  36     for arg in args[:1]:
  37         stream.write(str(arg))
  38     for arg in args[1:]:
  39         stream.write(sep)
  40         stream.write(str(arg))
  41     stream.write(term)

Code comparisons

These are some comparisons of current print statements with the equivalent code using the builtin (again, don't get too hung up on names here).

Standard printing:

   1 print 1, 2, 3
   2 output(1, 2, 3)

Printing without any spaces:

   1 print "%d%d%d" % (1, 2, 3)
   2 output(1, 2, 3, sep='')

Print as comma separated list:

   1 print "%d, %d%, d" % (1, 2, 3)
   2 output(1, 2, 3, sep=', ')

Print without a trailing newline:

   1 print 1, 2, 3,
   2 output(1, 2, 3, term='')

Print to a different stream:

   1 print >> sys.stderr, 1, 2, 3
   2 output(1, 2, 3, stream=sys.stderr)

Print a simple sequence:

   1 print " ".join(map(str, range(10)))
   2 output(*range(10))

Print a generator expression:

   1 print " ".join(str(x*x) for x in range(10))
   2 output(*(x*x for x in range(10)))

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