Variable s memory size in Python

Question

I am writing Python code to do some big number calculation  and have serious concern about the memory used in the calculation   Thus  I want to count every bit of each variable   For example  I have a variable x  which is a big number  and want to count the number of bits for representing x   The following code is obviously useless   x 2  1000 len x    Thus  I turn to use the following code   x 2  1000 len repr x     The variable x is  in decimal  is      10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376   but the above code returns 303  The above long long sequence is of length 302  and so I believe that 303 should be related to the string length only   So  here comes my original question   How can I know the memory size of variable x   One more thing  in C C   language  if I define  int z 1    This means that there are 4 bytes  32 bits allocated for z  and the bits are arranged as 00  001 31 0 s and one 1    Here  my variable x is huge  I don t know whether it follows the same memory allocation rule

User · Accepted Answer

Use sys getsizeof to get the size of an object  in bytes    gt  gt  gt  from sys import getsizeof  gt  gt  gt  a   42  gt  gt  gt  getsizeof a  12  gt  gt  gt  a   2  1000  gt  gt  gt  getsizeof a  146  gt  gt  gt    Note that the size and layout of an object is purely implementation-specific  CPython  for example  may use totally different internal data structures than IronPython  So the size of an object may vary from implementation to implementation

User · Answer

Regarding the internal structure of a Python long  check sys int info  or sys long info for Python 2 7     gt  gt  gt  import sys  gt  gt  gt  sys int info sys int info bits per digit 30  sizeof digit 4    Python either stores 30 bits into 4 bytes  most 64-bit systems  or 15 bits into 2 bytes  most 32-bit systems   Comparing the actual memory usage with calculated values  I get   gt  gt  gt  import math  sys  gt  gt  gt  a 0  gt  gt  gt  sys getsizeof a  24  gt  gt  gt  a 2  100  gt  gt  gt  sys getsizeof a  40  gt  gt  gt  a 2  1000  gt  gt  gt  sys getsizeof a  160  gt  gt  gt  24 4 math ceil 100 30  40  gt  gt  gt  24 4 math ceil 1000 30  160   There are 24 bytes of overhead for 0 since no bits are stored  The memory requirements for larger values matches the calculated values   If your numbers are so large that you are concerned about the 6 25  unused bits  you should probably look at the gmpy2 library  The internal representation uses all available bits and computations are significantly faster for large values  say  greater than 100 digits

[python] Variable's memory size in Python

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