Set literal confusion

[kaoruAngel]

I recently decided to implement a small project in python after being
away from the language for a while, so, in learning the language over
again, I experimented.

---------------------------------------
Python 3.1.1 (r311:74483, Aug 17 2009, 16:45:59) [MSC v.1500 64 bit
(AMD64)] on win32

True
False
False
False

{range(0, 10)}
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
------------------------------------------

After a few days of sitting on what seemed at first to be seemingly
buggy, inconsistent set-creation behaviour, I've finally decided it's
not a bug, but a misunderstanding of mine. However, that does still
leave me with one question: why does Python 3.1.1 allow me to get
caught up in my confusion while Python 3.0 (an EARLIER version) spouts
an error pointing me in the right direction? (see below for Python 3.0
behaviour)

----------------------------------------
Python 3.0 (r30:67507, Dec 3 2008, 20:14:27) [MSC v.1500 32 bit
(Intel)] on win32

True
False

Traceback (most recent call last):
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'range'

 

[Peter Otten]

I recently decided to implement a small project in python after being
away from the language for a while, so, in learning the language over
again, I experimented.

---------------------------------------
Python 3.1.1 (r311:74483, Aug 17 2009, 16:45:59) [MSC v.1500 64 bit
(AMD64)] on win32

True
False
False
False

{range(0, 10)}
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
------------------------------------------

After a few days of sitting on what seemed at first to be seemingly
buggy, inconsistent set-creation behaviour, I've finally decided it's
not a bug, but a misunderstanding of mine. However, that does still
leave me with one question: why does Python 3.1.1 allow me to get
caught up in my confusion while Python 3.0 (an EARLIER version) spouts
an error pointing me in the right direction? (see below for Python 3.0
behaviour)

That is probably a bug: http://bugs.python.org/issue4701

----------------------------------------
Python 3.0 (r30:67507, Dec 3 2008, 20:14:27) [MSC v.1500 32 bit
(Intel)] on win32

True
False

Traceback (most recent call last):
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'range'

My younger 3.0.1 doesn't show that behaviour:

Python 3.0.1+ (r301:69556, Apr 15 2009, 17:25:52)
[GCC 4.3.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.{range(0, 10)}

Peter

 

[Vlastimil Brom]

I recently decided to implement a small project in python after being
away from the language for a while, so, in learning the language over
again, I experimented.

---------------------------------------
Python 3.1.1 (r311:74483, Aug 17 2009, 16:45:59) [MSC v.1500 64 bit
(AMD64)] on win32

True
False
False
False

{range(0, 10)}
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}

You might also try the set comprehension:

Python 3.1 (r31:73574, Jun 26 2009, 20:21:35) [MSC v.1500 32 bit
(Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
For these simple cases without conditions, it probably doesn't make
much difference.
The character of the single items is maybe more obvious.

vbr

 

[Dennis Lee Bieber]

I recently decided to implement a small project in python after being
away from the language for a while, so, in learning the language over
again, I experimented.

Read the changes between 2.x and 3.x

False

range() is what used to be xrange() -- an on-demand generator of
values. You created a set containing a single generator. Try something
like:

5 in {list(range(10))}

 

[Peter Otten]

range() is what used to be xrange() -- an on-demand generator of
values. You created a set containing a single generator. Try something
like:

5 in {list(range(10))}

No. {expr} is always a set with a single element.
{range(0, 10)}

That element cannot be a list, by the way, because lists aren't hashable.
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

Peter

 

[Dennis Lee Bieber]

No. {expr} is always a set with a single element.

Accepted -- shows how often I use sets in my small jobs...

The main thing I was trying to implement was something that would
consume the generator leaving the values... Which probably means (again,
my set-less experience shows)

5 in set(range(10))

is the proper one <G>