详解python中的 is 操作符

class A():
 def __init__(self, v): 
  self.value = v
 def __eq__(self, t): 
  return self.value == t.value
a = A(3)
b = A(3)
print a == b
print a is b

a = 10
b = 10
print a is b
a = 10.0
b = 10.0
print a is b
a = 10
def f():
 return 10
print f() is a
a = 1000
def f():
 return 1000
print f() is a
a = 10.0
def f():
 return 10.0
print f() is a

a = 10
b = 10
print a is b
a = 10
def f():
 return 10
print f() is a

a = 10.0
b = 10.0
print a is b
a = 10.0
def f():
 return 10.0
print f() is a

python -m compileall testis.py

 <argcount> 0 </argcount>
 <nlocals> 0</nlocals>
 <stacksize> 2</stacksize>
 <flags> 0040</flags>
 <code>
  6400005a00006400005a01006500006501006b080047486400005a000064
  01008400005a02006502008300006500006b0800474864020053
 </code>
 <dis>
 1   0 LOAD_CONST    0 (10.0)
    3 STORE_NAME    0 (a)

 2   6 LOAD_CONST    0 (10.0)
    9 STORE_NAME    1 (b)

 3   12 LOAD_NAME    0 (a)
    15 LOAD_NAME    1 (b)
    18 COMPARE_OP    8 (is)
    21 PRINT_ITEM   
    22 PRINT_NEWLINE  

 5   23 LOAD_CONST    0 (10.0)
    26 STORE_NAME    0 (a)

 6   29 LOAD_CONST    1 (<code object f>)
    32 MAKE_FUNCTION   0
    35 STORE_NAME    2 (f)

 8   38 LOAD_NAME    2 (f)
    41 CALL_FUNCTION   0
    44 LOAD_NAME    0 (a)
    47 COMPARE_OP    8 (is)
    50 PRINT_ITEM   
    51 PRINT_NEWLINE  
    52 LOAD_CONST    2 (None)
    55 RETURN_VALUE  
 </dis>
 <names> ('a', 'b', 'f')</names>
 <varnames> ()</varnames>
 <freevars> ()</freevars>
 <cellvars> ()</cellvars>
 <filename> 'testis.py'</filename>
 <name> '<module>'</name>
 <firstlineno> 1</firstlineno>
 <consts>
  10.0
  <code>
   <argcount> 0 </argcount>
   <nlocals> 0</nlocals>
   <stacksize> 1</stacksize>
   <flags> 0043</flags>
   <code> 64010053</code>
   <dis>
 7   0 LOAD_CONST    1 (10.0)
    3 RETURN_VALUE  
   </dis>
   <names> ()</names>
   <varnames> ()</varnames>
   <freevars> ()</freevars>
   <cellvars> ()</cellvars>
   <filename> 'testis.py'</filename>
   <name> 'f'</name>
   <firstlineno> 6</firstlineno>
   <consts>
   None
   10.0
   </consts>
   <lnotab> 0001</lnotab>
  </code>
  None
 </consts>
 <lnotab> 060106010b0206010902</lnotab>