tuple syntax ',' (ending in comma?)

[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:

[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

[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.

[Lawrence D'Oliveiro]

In article <ma***************************************@python. org>,
"Michael Yanowitz" <m.********@kearfott.com> 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>