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Editor: NickCoghlan
Comment: Add the output function
Revision 5 as of 2005-09-03 01:53:26
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Editor: NickCoghlan
Comment: Change line terminator keyword to 'term'
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=== Benefits of using a function instead of a statement ===
 * Extended call syntax provides better interaction with sequences
 * Keyword argument `sep` allows separator to be changed easily and obviously
 * Keyword argument `term` allows line terminator to be changed easily and obviously
 * Keyword argument `stream` allows easy and obvious redirection
 * The builtin can be replaced for application wide customisation (e.g. per-thread logging)
 * Interacts well with PEP 309's partial function application

=== 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 :)
Line 13: Line 24:
    >>> output(1, 2, 3, end='Alternate line ending')
    1 2 3Alternate line ending
    >>> output(1, 2, 3, term='Alternate line terminator')
    1 2 3Alternate line terminator
Line 37: Line 48:
    sep, end, stream = kwds["sep"], kwds["end"], kwds["stream"]     sep, term, stream = kwds["sep"], kwds["term"], kwds["stream"]
Line 44: Line 55:
    stream.write(end)     stream.write(term)

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 an hacking of the grammar, and also makes a number of things significantly easier.

Benefits of using a function instead of a statement

  • Extended call syntax provides better interaction with sequences
  • Keyword argument sep allows separator to be changed easily and obviously

  • Keyword argument term allows line terminator to be changed easily and obviously

  • Keyword argument stream allows easy and obvious redirection

  • The builtin can be replaced for application wide customisation (e.g. per-thread logging)
  • Interacts well with PEP 309's partial function application

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         "end": "\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)

PrintAsFunction (last edited 2011-08-14 09:25:04 by eth595)

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