Re: tuple syntax ',' (ending in comma?)

2006-04-05 Thread Lawrence D'Oliveiro 
In article [EMAIL PROTECTED],
 Michael Yanowitz [EMAIL PROTECTED] wrote:

I am confused by the syntax for tuples.
...
   The way I fixed this error was I added an extra , (comma) to the tuple:
  thread.start_new_thread(read_data_thread, (strDataFilename,))

  I am just confused by the syntax. I am used to a comma meaning that there
should be another parameter after the comma and if no additional parameter
the comma would not be necessary.

http://python.org/doc/2.4.2/ref/parenthesized.html
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Re: tuple syntax ',' (ending in comma?)

2006-04-05 Thread Steven D'Aprano 
On Wed, 05 Apr 2006 08:17:07 +1000, Ben Finney wrote:

 Michael Yanowitz [EMAIL PROTECTED] writes:
 
I am still relatively new to Python. I am confused by the syntax
 for tuples.
 
 Well, it's reassuring to know that this is still as confusing for
 newcomers now as it was when I started.

With the introduction of generator expressions, I'm sure the next
generation of newcomers will have a brand new source of confusion whenever
they see a pair of parentheses, ensuring plenty of work for those writing
tutorials and books. And they say that language designers don't think of
the future.

*wink*



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tuple syntax ',' (ending in comma?)

2006-04-04 Thread Michael Yanowitz 
Hello:

   I am still relatively new to Python. I am confused by the syntax for
tuples.
I had:
  thread.start_new_thread(read_data_thread, (strDataFilename))
  and got back the following error:

  File scene.py, line 256, in readData
thread.start_new_thread(read_data_thread, (strDataFilename))
TypeError: 2nd arg must be a tuple

   The way I fixed this error was I added an extra , (comma) to the tuple:
  thread.start_new_thread(read_data_thread, (strDataFilename,))

  I am just confused by the syntax. I am used to a comma meaning that there
should be another parameter after the comma and if no additional parameter
the comma would not be necessary.

Thanks in advance:



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Re: tuple syntax ',' (ending in comma?)

2006-04-04 Thread Georg Brandl 
Michael Yanowitz wrote:
 Hello:
 
I am still relatively new to Python. I am confused by the syntax for
 tuples.
 I had:
   thread.start_new_thread(read_data_thread, (strDataFilename))
   and got back the following error:
 
   File scene.py, line 256, in readData
 thread.start_new_thread(read_data_thread, (strDataFilename))
 TypeError: 2nd arg must be a tuple
 
The way I fixed this error was I added an extra , (comma) to the tuple:
   thread.start_new_thread(read_data_thread, (strDataFilename,))
 
   I am just confused by the syntax. I am used to a comma meaning that there
 should be another parameter after the comma and if no additional parameter
 the comma would not be necessary.

What would you expect

 3 * (5 + 2)

to print? Certainly not (7, 7, 7), but it would if all expressions in
parentheses were tuples.

Thus, the comma is necessary to disambiguate and explicitly tell the parser
that you mean to construct a tuple.

Georg
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Re: tuple syntax ',' (ending in comma?)

2006-04-04 Thread John Salerno 
Michael Yanowitz wrote:

   I am just confused by the syntax. I am used to a comma meaning that there
 should be another parameter after the comma and if no additional parameter
 the comma would not be necessary.

But isn't it incorrect to think in terms of 'parameters' when referring 
to tuples? Tuples just contain elements, not parameters, so it might 
help not to think of it as function call syntax.
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Re: tuple syntax ',' (ending in comma?)

2006-04-04 Thread Ben Finney 
Michael Yanowitz [EMAIL PROTECTED] writes:

I am still relatively new to Python. I am confused by the syntax
 for tuples.

Well, it's reassuring to know that this is still as confusing for
newcomers now as it was when I started.

   File scene.py, line 256, in readData
 thread.start_new_thread(read_data_thread, (strDataFilename))
 TypeError: 2nd arg must be a tuple

Yes, parentheses are not sufficient (and often are unnecessary) to
make a tuple. The important syntax for a tuple is the comma.

URL:http://docs.python.org/lib/typesseq.html

 The way I fixed this error was I added an extra , (comma) to the
 tuple:

   thread.start_new_thread(read_data_thread, (strDataFilename,))

That's the correct way to do it, yes.

   I am just confused by the syntax. I am used to a comma meaning
 that there should be another parameter after the comma and if no
 additional parameter the comma would not be necessary.

This is a known wart, one that many people would like to see fixed.

For more discussion (which will likely be repeated in this thread),
see this thread from around this time last year:

URL:http://mail.python.org/pipermail/python-list/2005-March/271180.html

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  `\ action, where it often substitutes for both.  -- John Andrew |
_o__)  Holmes, _Wisdom in Small Doses_ |
Ben Finney

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