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What is the difference between 32 and 64 bit Python on Windows 7 64 bit?

+2 votes
309 views

I want to install Python on a PC with the 64 bit version of Windows 7. I want Python to be able to use as much as possible of the RAM.

When I install the 64 bit version of Python I find that sys.maxint == 2**31 - 1 Whereas the Pythpon installed on my 64 bit linux system returns sys.maxint == 2**63 - 1.

It looks to me as though 32 and 64 bit versions of Python on 64 bit Windows are both really 32 bit Python, differing only in how they interact with Windows. So I wouldnt expect 64 bit Python running on 64 bit Windows to allow the large data struictures I could have with 64 bit Python running on 64 bit linux.

Is that true?I have spent a couple of hours searching for a definitive description of the difference between the 32 and 64 bit versions of Python for Windows and haven't found anything.

posted May 11, 2014 by Abhay

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2 Answers

+1 vote

Since sys.maxint is gone in 3.x, you must be using some version of 2.x. Do yourself a favor and install 3.4 unless you absolutely need 2.x.

With 3.4:

 >>> a = [None]*1000000000
 >>> sys.getsizeof(a)
8000000064

That is 1000000000 8-byte pointers, as I expected.

answer May 11, 2014 by Bob Wise
0 votes

When I install the 64 bit version of Python I find that sys.maxint == 2**31 - 1 Whereas the Python installed on my 64 bit Linux system returns sys.maxint == 2**63 - 1.

That comes from the underlying C implementation. 64-bit MSVC still has long int as 32-bit. You need to specify long long int to get a 64-bit number even on a 64-bit compiler. Microsoft is a little nuts on the
backwards compatiblity.

Is that true? I have spent a couple of hours searching for a definitive description of the difference between the 32 and 64 bit versions of Python for Windows and haven't found anything.

long int (the size of an integer) != size_t (the size of an object). 64-bit Python still uses 64-bit pointers so it can still address more than 4GB of memory. It just rolls over into longs after 32-bit int max instead of after 64-bit int max.

answer May 11, 2014 by Amit Parthsarthi
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