Updates from Python SVN, Part 19

December 27, 2007 at 4:21 pm · tags: Python Python SVN

Here we are with another update from Python 2.x SVN.

• Added os.O_NOATIME constant. It serves the purpose to not update the access time within read operations.

• Added os.fchmod() and os.fchown().

• The new module has been deprecated. Use types instead.

• sys.py3kwarning flag has been exposed. True when python is started with -3 flag on command line. Also warning.warnpy3k() has been added to help the transition.

• Added PyFloat_GetMax, PyFloat_GetMin, PyFloat_GetInfo to the C API and float_info dictionary to the sys module which contains information about the internal floating point type.

• Added test suite for the cmd module.

• Added Python on Windows documentation.

• Implemented PEP 366 (Main module explicit relative imports).

• Support loading pickles of random.Random objects created on 32-bit systems on 64-bit systems, and vice versa. As a consequence of the change, Random pickles created by Python 2.6 cannot be loaded in Python 2.5.

• Changed GeneratorExit’s base class from Exception to BaseException.

• os.access now always returns True on Windows for any existing directory since there are no read only directories on Windows.

• Added msvcrt.getwch(), msvcrt.getwche(), msvcrt.putwch(), msvcrt.ungetwch() to handle wide chars.

• namedtuple.asdict and namedtuple.replace are now namedtuple._asdict() and namedtuple._replace()

• Dictionary construction had a speed-up of about 10%. There is a new opcode, STORE_MAP that saves the compiler from awkward stack manipulations and specializes for dicts using PyDict_SetItem instead of PyObject_SetItem. From the log message:

Old disassembly:
              0 BUILD_MAP                0
              3 DUP_TOP             
              4 LOAD_CONST               1 (1)
              7 ROT_TWO             
              8 LOAD_CONST               2 ('x')
             11 STORE_SUBSCR        
             12 DUP_TOP             
             13 LOAD_CONST               3 (2)
             16 ROT_TWO             
             17 LOAD_CONST               4 ('y')
             20 STORE_SUBSCR 

New disassembly:
              0 BUILD_MAP                0
              3 LOAD_CONST               1 (1)    
              6 LOAD_CONST               2 ('x')
              9 STORE_MAP                
             10 LOAD_CONST               3 (2)  
             13 LOAD_CONST               4 ('y')
             16 STORE_MAP

• Another optimization has been added: BUILD_MAP now has a meaning. It’s the estimated size of the dictionary. Allows dictionaries to be pre-sized (upto 255 elements) saving time lost to re-sizes with their attendant mallocs and re-insertions. Has zero effect on small dictionaries (5 elements or fewer), a slight benefit for dicts upto 22 elements (because they had to resize once anyway), and more benefit for dicts upto 255 elements (saving multiple resizes during the build-up and reducing the number of collisions on the first insertions). Beyond 255 elements, there is no addional benefit.

• Renamed Py_Size, Py_Type and Py_Refcnt to Py_SIZE, Py_TYPE and Py_REFCNT. Macros for compatibility are available.

• Added signal.set_wakeup_fd(). There is a correspondent C API as well: PySignal_SetWakeupFd.

• Slightly change in __ hash __ behavior and rich comparison: __ hash __ can be inherited when one __ lt __, __ le __, __ gt __, __ ge __ are overridden, as long as __ eq __ and __ ne __ aren’t.

• Improved performance of built-in any()/all() by avoiding PyIter_Next().

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