In [71]:

    

import sys


    

In [82]:

    

# python reuses small integer objects within its runtime.
x = None
print(sys.getrefcount(0))


    

    




2489

In [83]:

    

x = 0
print(sys.getrefcount(0))


    

    




2491

In [74]:

    

# for small objects, "is" and "==" are true.
print(0 == 0)
print(0 is 0)


    

    




True
True

In [95]:

    

# when does this end? somewhere between 100 and 1000.
for i in range(10):
    print ("value: %d, is-comparison: %s" % (10 ** i, 10 ** i is 10 ** i))


    

    




value: 1, is-comparison: True
value: 10, is-comparison: True
value: 100, is-comparison: True
value: 1000, is-comparison: False
value: 10000, is-comparison: False
value: 100000, is-comparison: False
value: 1000000, is-comparison: False
value: 10000000, is-comparison: False
value: 100000000, is-comparison: False
value: 1000000000, is-comparison: False

In [86]:

    

# the boundary is actually between 256 and 257!
sys.getrefcount(256)
print (256 + 0 is 256 + 0)


    

    




True

In [87]:

    

# bigger objects are not cached and created one off.
sys.getrefcount(257)
print (256 + 1 is 256 + 1)


    

    




False

In [91]:

    

# we had to use 256 + 1 to fight interpreter optimization.
# constant literals in a single statement uses same references.
lhs = 257
rhs = 257
print (lhs is rhs)
print (257 is 257)


    

    




False
True

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