How does Python manage int and long

Question

Does anybody know how Python manage internally int and long types     Does it choose the right type dynamically   What is the limit for an int  I am using Python 2 6  Is is different with previous versions    How should I understand the code below    gt  gt  gt  print type 65535   lt type  int  gt   gt  gt  gt  print type 65536 65536   lt type  long  gt    Update     gt  gt  gt  print type 0x7fffffff   lt type  int  gt   gt  gt  gt  print type 0x80000000   lt type  long  gt

User · Answer

Python 2 will automatically set the type based on the size of the value. A guide of max values can be found below.

The Max value of the default Int in Python 2 is 65535, anything above that will be a long

For example:

>> print type(65535)
<type 'int'>
>>> print type(65536*65536)
<type 'long'>

In Python 3 the long datatype has been removed and all integer values are handled by the Int class. The default size of Int will depend on your CPU architecture.

For example:

32 bit systems the default datatype for integers will be 'Int32'
64 bit systems the default datatype for integers will be 'Int64'

The min/max values of each type can be found below:

Int8: [-128,127]
Int16: [-32768,32767]
Int32: [-2147483648,2147483647]
Int64: [-9223372036854775808,9223372036854775807]
Int128: [-170141183460469231731687303715884105728,170141183460469231731687303715884105727]
UInt8: [0,255]
UInt16: [0,65535]
UInt32: [0,4294967295]
UInt64: [0,18446744073709551615]
UInt128: [0,340282366920938463463374607431768211455]

If the size of your Int exceeds the limits mentioned above, python will automatically change it's type and allocate more memory to handle this increase in min/max values. Where in Python 2, it would convert into 'long', it now just converts into the next size of Int.

Example: If you are using a 32 bit operating system, your max value of an Int will be 2147483647 by default. If a value of 2147483648 or more is assigned, the type will be changed to Int64.

There are different ways to check the size of the int and it's memory allocation. Note: In Python 3, using the built-in type() method will always return <class 'int'> no matter what size Int you are using.

User · Answer

On my machine    gt  gt  gt  print type 1 lt  lt 30   lt type  int  gt   gt  gt  gt  print type 1 lt  lt 31   lt type  long  gt   gt  gt  gt  print type 0x7FFFFFFF   lt type  int  gt   gt  gt  gt  print type 0x7FFFFFFF 1   lt type  long  gt    Python uses ints  32 bit signed integers  I don t know if they are C ints under the hood or not  for values that fit into 32 bit  but automatically switches to longs  arbitrarily large number of bits - i e  bignums   for anything larger  I m guessing this speeds things up for smaller values while avoiding any overflows with a seamless transition to bignums

User · Answer

int and long were  unified  a few versions back  Before that it was possible to overflow an int through math ops   3 x has further advanced this by eliminating long altogether and only having int    Python 2  sys maxint contains the maximum value a Python int can hold    On a 64-bit Python 2 7  the size is 24 bytes  Check with sys getsizeof     Python 3  sys maxsize contains the maximum size in bytes a Python int can be    This will be gigabytes in 32 bits  and exabytes in 64 bits  Such a large int would have a value similar to 8 to the power of sys maxsize

User · Answer

Interesting   On my 64-bit  i7 Ubuntu  box    gt  gt  gt  print type 0x7FFFFFFF   lt type  int  gt   gt  gt  gt  print type 0x7FFFFFFF 1   lt type  int  gt    Guess it steps up to 64 bit ints on a larger machine

User · Answer

Python 2 7 9 auto promotes numbers  For a case where one is unsure to use int   or long      gt  gt  gt  a   int  123    gt  gt  gt  type a   lt type  int  gt   gt  gt  gt  a   int  111111111111111111111111111111111111111111111111111    gt  gt  gt  type a   lt type  long  gt

User · Answer

Just to continue to all the answers that were given here  especially  James Lanes  the size of the integer type can be expressed by this formula   total range     2   bit system   lower limit   - 2   bit system  0 5 upper limit      2   bit system  0 5  - 1

User · Answer

This PEP should help    Bottom line is that you really shouldn t have to worry about it in python versions   2 4

User · Answer

It manages them because int and long are sibling class definitions   They have appropriate methods for    -        etc   that will produce results of the appropriate class   For example   gt  gt  gt  a 1 lt  lt 30  gt  gt  gt  type a   lt type  int  gt   gt  gt  gt  b a 2  gt  gt  gt  type b   lt type  long  gt    In this case  the class int has a   mul   method  the one that implements    which creates a long result when required

User · Answer

From python 3 x  the unified integer libries are even more smarter than older versions  On my  i7 Ubuntu  box I got the following    gt  gt  gt  type math factorial 30    lt class  int  gt    For implementation details refer Include longintrepr h  Objects longobject c and Modules mathmodule c files  The last file is a dynamic module  compiled to an so file   The code is well commented to follow

[python] How does Python manage int and long?

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