calculating the real size of a python string -

first of computer spec :

memory - https://gist.github.com/vyscond/6425304

cpu - https://gist.github.com/vyscond/6425322

so morning i've tested following 2 code snippets:

code a

a = 'a' * 1000000000 

and code b

a = 'a' * 10000000000 

the code works fine. code b give me error message :

traceback (most recent call last):   file "<stdin>", line 1, in <module> memoryerror 

so started researching method measuring size of data on python.

the first thing i've found classic built-in function len().

for code function len() returned value 1000000000, code b same memory error returned.

after decided more precision on tests. i've found function sys module called getsizeof(). function made same test on code a:

sys.getsizeof( 'a' * 1000000000 ) 

the result return 1000000037 (in bytes)

• question 1 - means 0.9313226090744 gigabytes?

so checked amount of bytes of string single character 'a'

sys.getsizeof( 'a' ) 

the result return 38 (in bytes)

• question 02 - means if need string composed of 1000000000 character 'a' result in 38 * 1000000000 = 38.000.000.000 bytes?

• question 03 - means need 35.390257835388 gigabytes hold string this?

i know error in reasoning! because not sense me '-'

python objects have minimal size, overhead of keeping several pieces of bookkeeping data attached object.

a python str object no exception. take @ difference between string no, one, 2 , 3 characters:

>>> import sys >>> sys.getsizeof('') 37 >>> sys.getsizeof('a') 38 >>> sys.getsizeof('aa') 39 >>> sys.getsizeof('aaa') 40 

the python str object overhead 37 bytes on machine, each character in string takes 1 byte on fixed overhead.

thus, str value 1000 million characters requires 1000 million bytes + 37 bytes overhead of memory. indeed 0.931 gigabytes.

your sample code 'b' created ten times more characters, needed 10 gigabyte of memory hold 1 string, not counting rest of python, , os , whatever else might running on machine.