From my interpreter prompt:
[color=blue][color=green][color=darkred]
>>> tuple = ("blah")
>>> len(tuple)[/color][/color][/color]
4[color=blue][color=green][color=darkred]
>>> tuple2 = ("blah",)
>>> len (tuple2)[/color][/color][/color]
1

So why is a tuple containing the string "blah" without the comma of
length four? Is there a good reason for this or is this a bug?

--

Carl J. Van Arsdall
cvanarsdall@mvista.com
Build and Release
MontaVista Software

Carl J. Van Arsdall wrote:
[color=blue]
>
> From my interpreter prompt:
>[color=green][color=darkred]
> >>> tuple = ("blah")
> >>> len(tuple)[/color][/color]
> 4[color=green][color=darkred]
> >>> tuple2 = ("blah",)
> >>> len (tuple2)[/color][/color]
> 1
>
> So why is a tuple containing the string "blah" without the comma of
> length four? Is there a good reason for this or is this a bug?
>[/color]

Hello,

Thats because the expression ("blah") actually resolves to "blah" instead of
a tuple containing the string "blah".
[color=blue][color=green][color=darkred]
>>> type(("spam"))[/color][/color][/color]
<type 'str'>

Adding a comma after spam results in the tuple being created.
[color=blue][color=green][color=darkred]
>>> type(("spam",))[/color][/color][/color]
<type 'tuple'>

And to make things even more confusing, just adding a comma without braces
will give you a tuple too.
[color=blue][color=green][color=darkred]
>>> "spam",[/color][/color][/color]
('spam',)

The explanation for this all can be found at:
http://docs.python.org/ref/parenthesized.html

Regards,

Maas

On Wed, 14 Dec 2005 09:54:31 -0800, Carl J. Van Arsdall wrote:
[color=blue]
>
> From my interpreter prompt:
>[color=green][color=darkred]
> >>> tuple = ("blah")[/color][/color][/color]

There is a special place in Hell reserved for people who overwrite
built-in functions like tuple(), list(), str() and so forth. *wink*

[color=blue][color=green][color=darkred]
> >>> len(tuple)[/color][/color]
> 4[/color]

Brackets on their own are just used for grouping, so ("blah") is the same
as just "blah", namely a string with four characters.

The only exception to this is the empty tuple, which is made with an empty ().

[color=blue][color=green][color=darkred]
> >>> tuple2 = ("blah",)
> >>> len (tuple2)[/color][/color]
> 1[/color]

Tuples are made with commas, not brackets. You could write just "blah",
without the brackets and it would still work.

py> t = "blah",
py> t
('blah',)

[color=blue]
> So why is a tuple containing the string "blah" without the comma of
> length four? Is there a good reason for this or is this a bug?[/color]

It's not a bug.


--
Steven.

Carl J. Van Arsdall wrote:[color=blue]
>
> From my interpreter prompt:
>[color=green][color=darkred]
>>>> tuple = ("blah")
>>>> len(tuple)[/color][/color]
> 4[color=green][color=darkred]
>>>> tuple2 = ("blah",)
>>>> len (tuple2)[/color][/color]
> 1
>
> So why is a tuple containing the string "blah" without the comma of
> length four? Is there a good reason for this or is this a bug?[/color]

Additional note:

You should not give a tuple a variable name of tuple, it masks
the built-in tuple() function. This also goes for str, or other
built-ins. This will "bite" you at some point if it hasn't already.

-Larry Bates