PyFloat_FromString() is very restrictive.  In our case, for example, the floats in question don't come from text files.

I'm adding a new file with changes suggested by Antoine.  only 0.0 and 1.0 are interned.  It turns out that the "int" test is expensive, and special casing it to check for '0.0' and '1.0' with direct float comparison makes the performance hit go away.  Here are the figures:


D:\pydev\hg\cpython2>pcbuild10\python.exe Tools\pybench\pybench.py -s interned8 -c normal
-------------------------------------------------------------------------------
PYBENCH 2.1
-------------------------------------------------------------------------------
* using CPython 3.3.0a1+ (default, Mar 22 2012, 15:39:50) [MSC v.1600 32 bit (Intel)]
* disabled garbage collection
* system check interval set to maximum: 2147483647
* using timer: time.clock

-------------------------------------------------------------------------------
Benchmark: interned8
-------------------------------------------------------------------------------

    Rounds: 10
    Warp:   10
    Timer:  time.clock

    Machine Details:
       Platform ID:    Windows-7-6.1.7601-SP1
       Processor:      Intel64 Family 6 Model 26 Stepping 5, GenuineIntel

    Python:
       Implementation: CPython
       Executable:     D:\pydev\hg\cpython2\pcbuild10\python.exe
       Version:        3.3.0a1+
       Compiler:       MSC v.1600 32 bit (Intel)
       Bits:           32bit
       Build:          Mar 22 2012 15:39:50 (#default)
       Unicode:        UCS4


-------------------------------------------------------------------------------
Comparing with: normal
-------------------------------------------------------------------------------

    Rounds: 10
    Warp:   10
    Timer:  time.clock

    Machine Details:
       Platform ID:    Windows-7-6.1.7601-SP1
       Processor:      Intel64 Family 6 Model 26 Stepping 5, GenuineIntel

    Python:
       Implementation: CPython
       Executable:     D:\pydev\hg\cpython2\pcbuild10\python.exe
       Version:        3.3.0a1+
       Compiler:       MSC v.1600 32 bit (Intel)
       Bits:           32bit
       Build:          Mar 22 2012 13:53:45 (#default)
       Unicode:        UCS4


Test                             minimum run-time        average  run-time
                                 this    other   diff    this    other   diff
-------------------------------------------------------------------------------
          BuiltinFunctionCalls:    59ms    59ms   -0.7%    60ms    60ms   -0.3%
           BuiltinMethodLookup:    40ms    40ms   -0.2%    40ms    40ms   -0.2%
                 CompareFloats:    47ms    46ms   +2.3%    47ms    46ms   +2.3%
         CompareFloatsIntegers:   125ms   126ms   -0.8%   129ms   131ms   -2.0%
               CompareIntegers:    76ms    76ms   -0.2%    76ms    76ms   -0.3%
        CompareInternedStrings:    60ms    60ms   -0.0%    61ms    61ms   +0.2%
                  CompareLongs:    44ms    44ms   -0.4%    44ms    44ms   -0.4%
                CompareStrings:    59ms    58ms   +2.1%    59ms    58ms   +1.8%
    ComplexPythonFunctionCalls:    59ms    60ms   -1.7%    60ms    61ms   -2.5%
                 ConcatStrings:    49ms    55ms  -10.7%    49ms    55ms  -10.6%
               CreateInstances:    67ms    66ms   +1.1%    68ms    68ms   -0.1%
            CreateNewInstances:    50ms    50ms   +1.3%    51ms    50ms   +0.4%
       CreateStringsWithConcat:    70ms    71ms   -1.3%    70ms    72ms   -1.7%
                  DictCreation:    45ms    46ms   -1.7%    46ms    46ms   -1.5%
             DictWithFloatKeys:    81ms    84ms   -2.8%    81ms    84ms   -2.7%
           DictWithIntegerKeys:    52ms    55ms   -5.4%    52ms    55ms   -5.1%
            DictWithStringKeys:    47ms    51ms   -6.6%    48ms    51ms   -6.6%
                      ForLoops:    42ms    42ms   +0.2%    42ms    42ms   +0.2%
                    IfThenElse:    63ms    59ms   +5.5%    63ms    59ms   +5.6%
                   ListSlicing:    39ms    39ms   +0.0%    39ms    39ms   -0.4%
                NestedForLoops:    67ms    67ms   -0.2%    68ms    68ms   +0.0%
      NestedListComprehensions:    63ms    62ms   +1.2%    64ms    63ms   +1.2%
          NormalClassAttribute:   102ms   100ms   +1.3%   102ms   101ms   +1.4%
       NormalInstanceAttribute:    62ms    62ms   +0.2%    63ms    63ms   +0.2%
           PythonFunctionCalls:    60ms    60ms   +0.8%    61ms    60ms   +1.3%
             PythonMethodCalls:    74ms    74ms   -0.0%    74ms    74ms   -0.3%
                     Recursion:   103ms   102ms   +1.4%   104ms   102ms   +1.3%
                  SecondImport:   109ms   109ms   -0.4%   110ms   110ms   -0.6%
           SecondPackageImport:   111ms   112ms   -0.6%   113ms   113ms   +0.2%
         SecondSubmoduleImport:   154ms   153ms   +0.7%   155ms   155ms   -0.2%
       SimpleComplexArithmetic:    56ms    54ms   +3.7%    57ms    56ms   +1.9%
        SimpleDictManipulation:    94ms    93ms   +0.3%    94ms    94ms   -0.2%
         SimpleFloatArithmetic:    45ms    44ms   +3.2%    45ms    45ms   +1.7%
      SimpleIntFloatArithmetic:    57ms    56ms   +1.8%    57ms    57ms   +0.1%
       SimpleIntegerArithmetic:    56ms    56ms   +1.2%    57ms    56ms   +1.0%
      SimpleListComprehensions:    53ms    52ms   +1.8%    54ms    53ms   +2.4%
        SimpleListManipulation:    49ms    53ms   -8.0%    50ms    53ms   -6.7%
          SimpleLongArithmetic:    41ms    40ms   +1.6%    41ms    41ms   +0.1%
                    SmallLists:    66ms    68ms   -2.8%    67ms    68ms   -2.5%
                   SmallTuples:    76ms    72ms   +5.5%    76ms    72ms   +5.8%
         SpecialClassAttribute:   144ms   140ms   +2.8%   145ms   142ms   +2.1%
      SpecialInstanceAttribute:    64ms    64ms   +0.7%    65ms    64ms   +1.1%
                StringMappings:   126ms   132ms   -4.2%   127ms   132ms   -4.0%
              StringPredicates:    71ms    70ms   +2.3%    72ms    70ms   +2.5%
                 StringSlicing:    66ms    67ms   -0.6%    67ms    67ms   -1.1%
                     TryExcept:    44ms    43ms   +1.5%    44ms    44ms   +0.7%
                    TryFinally:    49ms    53ms   -7.4%    49ms    54ms   -8.1%
                TryRaiseExcept:    24ms    22ms   +8.6%    25ms    23ms   +8.9%
                  TupleSlicing:    61ms    61ms   -0.7%    61ms    62ms   -0.5%
                   WithFinally:    65ms    65ms   -0.3%    65ms    65ms   -0.0%
               WithRaiseExcept:    62ms    62ms   -0.4%    62ms    63ms   -0.6%
-------------------------------------------------------------------------------
Totals:                          3448ms  3454ms   -0.2%  3474ms  3487ms   -0.4%

(this=interned8, other=normal)


D:\pydev\hg\cpython2>