I'm quite new to python, so I'm doing my usual of going through Project Euler to work out the logical kinks in my head.
Basically, I need the largest list size possible, ie range(1,n), without overflowing.
Any ideas?
A:
The size of your lists is only limited by your memory. Note that, depending on your version of Python, range(1, 9999999999999999) needs only a few bytes of RAM since it always only creates a single element of the virtual list it returns.
If you want to instantiate the list, use list(range(1,n)) (this will copy the virtual list).
Aaron Digulla
2010-07-14 15:52:42
Are you assuming 3.x? On 2.x this is incorrect for the reason given in my own answer, and on 3.x it's still incorrect as long as you interpret "list" literally: list size is bound by `ssize_t` . Anyway, it's really silly to simply assume people are using 3.x .
Devin Jeanpierre
2010-07-14 15:56:50
There is no doubt he's assuming 3.x; `sys.getsizeof(range(1e8))` returns `400000036` on 2.6 (and takes a noticeable time to compute). The 3.x analogy would be `sys.getsizeof(xrange(1e8))` that gives `20` and is instant.
Nick T
2010-07-14 16:49:43
Which part if "depending on your version of Python" didn't you understand? :-(
Aaron Digulla
2010-07-15 10:15:44
+3
A:
Look at get_len_of_range and get_len_of_range_longs in the builtin module source
Summary: You'll get an OverflowError if the list has more elements than can be fit into a signed long. On 32bit Python that's 2**31 - 1, and on 64 bit Python that's 2**63 - 1. Of course, you will get a MemoryError even for values just under that.
Devin Jeanpierre
2010-07-14 15:56:24
I thought that the `sys.maxsize` limit only applied to `xrange`, not to Python 2's `range`. Of course it's pretty academic unless you have a great deal of memory...
Scott Griffiths
2010-07-14 16:00:24
Quick follow up question; any easy way to query python as to how much it can cope with at the minute?
Andrew Bolster
2010-07-14 16:18:08