Question about tuple lengths

[Carl J. Van Arsdall]

From my interpreter prompt:

tuple = ("blah")
len(tuple) 4 tuple2 = ("blah",)
len (tuple2)

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
cv*********@mvista.com
Build and Release
MontaVista Software

[MM Zeeman]

Carl J. Van Arsdall wrote:

From my interpreter prompt:

>>> tuple = ("blah")
>>> len(tuple) 4 >>> tuple2 = ("blah",)
>>> len (tuple2) 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?

Hello,

Thats because the expression ("blah") actually resolves to "blah" instead of
a tuple containing the string "blah".

type(("spam")) <type 'str'>

Adding a comma after spam results in the tuple being created.
type(("spam",)) <type 'tuple'>

And to make things even more confusing, just adding a comma without braces
will give you a tuple too.
"spam",

('spam',)

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

Regards,

Maas

[Steven D'Aprano]

On Wed, 14 Dec 2005 09:54:31 -0800, Carl J. Van Arsdall wrote:

From my interpreter prompt:

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

>>> len(tuple) 4
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 ().

>>> tuple2 = ("blah",)
>>> len (tuple2)

1

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',)

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?

It's not a bug.
--
Steven.

[Larry Bates]

Carl J. Van Arsdall wrote:

From my interpreter prompt:

tuple = ("blah")
len(tuple) 4 tuple2 = ("blah",)
len (tuple2)

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?

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