----- Original Message -----
> From: Steven D'Aprano <st...@pearwood.info>
> To: tutor@python.org
> Cc:
> Sent: Friday, June 13, 2014 3:08 PM
> Subject: Re: [Tutor] global variables/constants versus volatile
> variables/constants
>
> On Fri, Jun 13, 2014 at 05:10:28AM -0700, Albert-Jan Roskam wrote:
>
>> The other day I used collections.namedtuple and I re-initialized
>> Record (see below) with every function*) call. Bad idea! It looks
>> nicer because I did not need a global (and globals are baaad, mkay?),
>> but it was *much* slower. I processed a log of a few million lines, I
>> think.
>>
>> # bad --> time-consuming
>> import collections
>>
>> def do_something_with(raw_record):
>> Record = collections.namedtuple("_", "
> ".join("v%%03d" % i for i in range(100)))
>> return Record(*raw_record.split())
>
> Look at how much work you do here. First, you create a long string of
> the form:
>
> "v000 v001 v002 v003 ... v099"
>
> representing 1000 v-digits names. Then you create a brand new Record
> class that takes those 100 v-digits names as arguments. Creating that
> class requires building a string, parsing it as Python code, and then
> running it. (You're not expected to know that, but if you read the
> source code for namedtuple you will see that's how it works.) So
> creating that class is slow. Every time you call the function, it builds
> a new "v000 ... v099" string, from scratch, then builds a new class,
> also from scratch, and finally populates an instance of that class with
> 100 values from the raw_record.
>
> Only that last step needs to be done inside the function.
Hmm, if I create the namedtuple with 'verbose=True' it *really* makes clear why
it took so much longer.
(what's '_property' btw? I know 'property' and the newer decorator wih the same
name, but not _property).
In [1]: import collections
In [2]: Record = collections.namedtuple("_", " ".join("v%03d" % i for i in
range(100)),verbose=True)
class _(tuple):
'_(v000, v001, v002, v003, v004, v005, v006, v007, v008, v009, v010, v011,
v012, v013, v014, v015, v016, v017, v018, v019, v020, v021, v022, v023, v024,
v025, v026, v027, v028, v029, v030, v031, v032, v033, v034, v035, v036, v037,
v038, v039, v040, v041, v042, v043, v044, v045, v046, v047, v048, v049, v050,
v051, v052, v053, v054, v055, v056, v057, v058, v059, v060, v061, v062, v063,
v064, v065, v066, v067, v068, v069, v070, v071, v072, v073, v074, v075, v076,
v077, v078, v079, v080, v081, v082, v083, v084, v085, v086, v087, v088, v089,
v090, v091, v092, v093, v094, v095, v096, v097, v098, v099)'
__slots__ = ()
_fields = ('v000', 'v001', 'v002', 'v003', 'v004', 'v005', 'v006', 'v007',
'v008', 'v009', 'v010', 'v011', 'v012', 'v013', 'v014', 'v015', 'v016', 'v017',
'v018', 'v019', 'v020', 'v021', 'v022', 'v023', 'v024', 'v025', 'v026', 'v027',
'v028', 'v029', 'v030', 'v031', 'v032', 'v033', 'v034', 'v035', 'v036', 'v037',
'v038', 'v039', 'v040', 'v041', 'v042', 'v043', 'v044', 'v045', 'v046', 'v047',
'v048', 'v049', 'v050', 'v051', 'v052', 'v053', 'v054', 'v055', 'v056', 'v057',
'v058', 'v059', 'v060', 'v061', 'v062', 'v063', 'v064', 'v065', 'v066', 'v067',
'v068', 'v069', 'v070', 'v071', 'v072', 'v073', 'v074', 'v075', 'v076', 'v077',
'v078', 'v079', 'v080', 'v081', 'v082', 'v083', 'v084', 'v085', 'v086', 'v087',
'v088', 'v089', 'v090', 'v091', 'v092', 'v093', 'v094', 'v095', 'v096', 'v097',
'v098', 'v099')
def __new__(_cls, v000, v001, v002, v003, v004, v005, v006, v007, v008,
v009, v010, v011, v012, v013, v014, v015, v016, v017, v018, v019, v020, v021,
v022, v023, v024, v025, v026, v027, v028, v029, v030, v031, v032, v033, v034,
v035, v036, v037, v038, v039, v040, v041, v042, v043, v044, v045, v046, v047,
v048, v049, v050, v051, v052, v053, v054, v055, v056, v057, v058, v059, v060,
v061, v062, v063, v064, v065, v066, v067, v068, v069, v070, v071, v072, v073,
v074, v075, v076, v077, v078, v079, v080, v081, v082, v083, v084, v085, v086,
v087, v088, v089, v090, v091, v092, v093, v094, v095, v096, v097, v098, v099):
'Create new instance of _(v000, v001, v002, v003, v004, v005, v006,
v007, v008, v009, v010, v011, v012, v013, v014, v015, v016, v017, v018, v019,
v020, v021, v022, v023, v024, v025, v026, v027, v028, v029, v030, v031, v032,
v033, v034, v035, v036, v037, v038, v039, v040, v041, v042, v043, v044, v045,
v046, v047, v048, v049, v050, v051, v052, v053, v054, v055, v056, v057, v058,
v059, v060, v061, v062, v063, v064, v065, v066, v067, v068, v069, v070, v071,
v072, v073, v074, v075, v076, v077, v078, v079, v080, v081, v082, v083, v084,
v085, v086, v087, v088, v089, v090, v091, v092, v093, v094, v095, v096, v097,
v098, v099)'
return _tuple.__new__(_cls, (v000, v001, v002, v003, v004, v005, v006,
v007, v008, v009, v010, v011, v012, v013, v014, v015, v016, v017, v018, v019,
v020, v021, v022, v023, v024, v025, v026, v027, v028, v029, v030, v031, v032,
v033, v034, v035, v036, v037, v038, v039, v040, v041, v042, v043, v044, v045,
v046, v047, v048, v049, v050, v051, v052, v053, v054, v055, v056, v057, v058,
v059, v060, v061, v062, v063, v064, v065, v066, v067, v068, v069, v070, v071,
v072, v073, v074, v075, v076, v077, v078, v079, v080, v081, v082, v083, v084,
v085, v086, v087, v088, v089, v090, v091, v092, v093, v094, v095, v096, v097,
v098, v099))
@classmethod
def _make(cls, iterable, new=tuple.__new__, len=len):
'Make a new _ object from a sequence or iterable'
result = new(cls, iterable)
if len(result) != 100:
raise TypeError('Expected 100 arguments, got %d' % len(result))
return result
def __repr__(self):
'Return a nicely formatted representation string'
return '_(v000=%r, v001=%r, v002=%r, v003=%r, v004=%r, v005=%r,
v006=%r, v007=%r, v008=%r, v009=%r, v010=%r, v011=%r, v012=%r, v013=%r,
v014=%r, v015=%r, v016=%r, v017=%r, v018=%r, v019=%r, v020=%r, v021=%r,
v022=%r, v023=%r, v024=%r, v025=%r, v026=%r, v027=%r, v028=%r, v029=%r,
v030=%r, v031=%r, v032=%r, v033=%r, v034=%r, v035=%r, v036=%r, v037=%r,
v038=%r, v039=%r, v040=%r, v041=%r, v042=%r, v043=%r, v044=%r, v045=%r,
v046=%r, v047=%r, v048=%r, v049=%r, v050=%r, v051=%r, v052=%r, v053=%r,
v054=%r, v055=%r, v056=%r, v057=%r, v058=%r, v059=%r, v060=%r, v061=%r,
v062=%r, v063=%r, v064=%r, v065=%r, v066=%r, v067=%r, v068=%r, v069=%r,
v070=%r, v071=%r, v072=%r, v073=%r, v074=%r, v075=%r, v076=%r, v077=%r,
v078=%r, v079=%r, v080=%r, v081=%r, v082=%r, v083=%r, v084=%r, v085=%r,
v086=%r, v087=%r, v088=%r, v089=%r, v090=%r, v091=%r, v092=%r, v093=%r,
v094=%r, v095=%r, v096=%r, v097=%r, v098=%r, v099=%r)' % self
def _asdict(self):
'Return a new OrderedDict which maps field names to their values'
return OrderedDict(zip(self._fields, self))
__dict__ = property(_asdict)
def _replace(_self, **kwds):
'Return a new _ object replacing specified fields with new values'
result = _self._make(map(kwds.pop, ('v000', 'v001', 'v002', 'v003',
'v004', 'v005', 'v006', 'v007', 'v008', 'v009', 'v010', 'v011', 'v012', 'v013',
'v014', 'v015', 'v016', 'v017', 'v018', 'v019', 'v020', 'v021', 'v022', 'v023',
'v024', 'v025', 'v026', 'v027', 'v028', 'v029', 'v030', 'v031', 'v032', 'v033',
'v034', 'v035', 'v036', 'v037', 'v038', 'v039', 'v040', 'v041', 'v042', 'v043',
'v044', 'v045', 'v046', 'v047', 'v048', 'v049', 'v050', 'v051', 'v052', 'v053',
'v054', 'v055', 'v056', 'v057', 'v058', 'v059', 'v060', 'v061', 'v062', 'v063',
'v064', 'v065', 'v066', 'v067', 'v068', 'v069', 'v070', 'v071', 'v072', 'v073',
'v074', 'v075', 'v076', 'v077', 'v078', 'v079', 'v080', 'v081', 'v082', 'v083',
'v084', 'v085', 'v086', 'v087', 'v088', 'v089', 'v090', 'v091', 'v092', 'v093',
'v094', 'v095', 'v096', 'v097', 'v098', 'v099'), _self))
if kwds:
raise ValueError('Got unexpected field names: %r' % kwds.keys())
return result
def __getnewargs__(self):
'Return self as a plain tuple. Used by copy and pickle.'
return tuple(self)
v000 = _property(_itemgetter(0), doc='Alias for field number 0')
v001 = _property(_itemgetter(1), doc='Alias for field number 1')
v002 = _property(_itemgetter(2), doc='Alias for field number 2')
v003 = _property(_itemgetter(3), doc='Alias for field number 3')
v004 = _property(_itemgetter(4), doc='Alias for field number 4')
v005 = _property(_itemgetter(5), doc='Alias for field number 5')
v006 = _property(_itemgetter(6), doc='Alias for field number 6')
v007 = _property(_itemgetter(7), doc='Alias for field number 7')
v008 = _property(_itemgetter(8), doc='Alias for field number 8')
v009 = _property(_itemgetter(9), doc='Alias for field number 9')
v010 = _property(_itemgetter(10), doc='Alias for field number 10')
v011 = _property(_itemgetter(11), doc='Alias for field number 11')
v012 = _property(_itemgetter(12), doc='Alias for field number 12')
v013 = _property(_itemgetter(13), doc='Alias for field number 13')
v014 = _property(_itemgetter(14), doc='Alias for field number 14')
v015 = _property(_itemgetter(15), doc='Alias for field number 15')
v016 = _property(_itemgetter(16), doc='Alias for field number 16')
v017 = _property(_itemgetter(17), doc='Alias for field number 17')
v018 = _property(_itemgetter(18), doc='Alias for field number 18')
v019 = _property(_itemgetter(19), doc='Alias for field number 19')
v020 = _property(_itemgetter(20), doc='Alias for field number 20')
v021 = _property(_itemgetter(21), doc='Alias for field number 21')
v022 = _property(_itemgetter(22), doc='Alias for field number 22')
v023 = _property(_itemgetter(23), doc='Alias for field number 23')
v024 = _property(_itemgetter(24), doc='Alias for field number 24')
v025 = _property(_itemgetter(25), doc='Alias for field number 25')
v026 = _property(_itemgetter(26), doc='Alias for field number 26')
v027 = _property(_itemgetter(27), doc='Alias for field number 27')
v028 = _property(_itemgetter(28), doc='Alias for field number 28')
v029 = _property(_itemgetter(29), doc='Alias for field number 29')
v030 = _property(_itemgetter(30), doc='Alias for field number 30')
v031 = _property(_itemgetter(31), doc='Alias for field number 31')
v032 = _property(_itemgetter(32), doc='Alias for field number 32')
v033 = _property(_itemgetter(33), doc='Alias for field number 33')
v034 = _property(_itemgetter(34), doc='Alias for field number 34')
v035 = _property(_itemgetter(35), doc='Alias for field number 35')
v036 = _property(_itemgetter(36), doc='Alias for field number 36')
v037 = _property(_itemgetter(37), doc='Alias for field number 37')
v038 = _property(_itemgetter(38), doc='Alias for field number 38')
v039 = _property(_itemgetter(39), doc='Alias for field number 39')
v040 = _property(_itemgetter(40), doc='Alias for field number 40')
v041 = _property(_itemgetter(41), doc='Alias for field number 41')
v042 = _property(_itemgetter(42), doc='Alias for field number 42')
v043 = _property(_itemgetter(43), doc='Alias for field number 43')
v044 = _property(_itemgetter(44), doc='Alias for field number 44')
v045 = _property(_itemgetter(45), doc='Alias for field number 45')
v046 = _property(_itemgetter(46), doc='Alias for field number 46')
v047 = _property(_itemgetter(47), doc='Alias for field number 47')
v048 = _property(_itemgetter(48), doc='Alias for field number 48')
v049 = _property(_itemgetter(49), doc='Alias for field number 49')
v050 = _property(_itemgetter(50), doc='Alias for field number 50')
v051 = _property(_itemgetter(51), doc='Alias for field number 51')
v052 = _property(_itemgetter(52), doc='Alias for field number 52')
v053 = _property(_itemgetter(53), doc='Alias for field number 53')
v054 = _property(_itemgetter(54), doc='Alias for field number 54')
v055 = _property(_itemgetter(55), doc='Alias for field number 55')
v056 = _property(_itemgetter(56), doc='Alias for field number 56')
v057 = _property(_itemgetter(57), doc='Alias for field number 57')
v058 = _property(_itemgetter(58), doc='Alias for field number 58')
v059 = _property(_itemgetter(59), doc='Alias for field number 59')
v060 = _property(_itemgetter(60), doc='Alias for field number 60')
v061 = _property(_itemgetter(61), doc='Alias for field number 61')
v062 = _property(_itemgetter(62), doc='Alias for field number 62')
v063 = _property(_itemgetter(63), doc='Alias for field number 63')
v064 = _property(_itemgetter(64), doc='Alias for field number 64')
v065 = _property(_itemgetter(65), doc='Alias for field number 65')
v066 = _property(_itemgetter(66), doc='Alias for field number 66')
v067 = _property(_itemgetter(67), doc='Alias for field number 67')
v068 = _property(_itemgetter(68), doc='Alias for field number 68')
v069 = _property(_itemgetter(69), doc='Alias for field number 69')
v070 = _property(_itemgetter(70), doc='Alias for field number 70')
v071 = _property(_itemgetter(71), doc='Alias for field number 71')
v072 = _property(_itemgetter(72), doc='Alias for field number 72')
v073 = _property(_itemgetter(73), doc='Alias for field number 73')
v074 = _property(_itemgetter(74), doc='Alias for field number 74')
v075 = _property(_itemgetter(75), doc='Alias for field number 75')
v076 = _property(_itemgetter(76), doc='Alias for field number 76')
v077 = _property(_itemgetter(77), doc='Alias for field number 77')
v078 = _property(_itemgetter(78), doc='Alias for field number 78')
v079 = _property(_itemgetter(79), doc='Alias for field number 79')
v080 = _property(_itemgetter(80), doc='Alias for field number 80')
v081 = _property(_itemgetter(81), doc='Alias for field number 81')
v082 = _property(_itemgetter(82), doc='Alias for field number 82')
v083 = _property(_itemgetter(83), doc='Alias for field number 83')
v084 = _property(_itemgetter(84), doc='Alias for field number 84')
v085 = _property(_itemgetter(85), doc='Alias for field number 85')
v086 = _property(_itemgetter(86), doc='Alias for field number 86')
v087 = _property(_itemgetter(87), doc='Alias for field number 87')
v088 = _property(_itemgetter(88), doc='Alias for field number 88')
v089 = _property(_itemgetter(89), doc='Alias for field number 89')
v090 = _property(_itemgetter(90), doc='Alias for field number 90')
v091 = _property(_itemgetter(91), doc='Alias for field number 91')
v092 = _property(_itemgetter(92), doc='Alias for field number 92')
v093 = _property(_itemgetter(93), doc='Alias for field number 93')
v094 = _property(_itemgetter(94), doc='Alias for field number 94')
v095 = _property(_itemgetter(95), doc='Alias for field number 95')
v096 = _property(_itemgetter(96), doc='Alias for field number 96')
v097 = _property(_itemgetter(97), doc='Alias for field number 97')
v098 = _property(_itemgetter(98), doc='Alias for field number 98')
v099 = _property(_itemgetter(99), doc='Alias for field number 99')
<snip>
> Global variables aren't bad because Moses came down from the mountains
> with a stone tablet that declares that they are bad. They're bad because
> they cause excessive coupling, they operate by side-effect, they spoil
> idepotent code, and they are implicit instead of explicit.
LOL :-) Textbooks conditioned me to have a generalized fear of globals. Like
Little Albert: http://en.wikipedia.org/wiki/Little_Albert_experiment :-)
>> def do_something_with(raw_record):
>> return Record(*raw_record.split())
>
> Much more sensible!
>
>
>
>
> --
> Steven
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