[Tutor] global variables/constants versus volatile variables/constants
diliup gabadamudalige
diliupg at gmail.com
Fri Jun 13 20:20:53 CEST 2014
pardon my ignorance. last few questions.
I declare the following dict at the beginning of the program.
KEY_SIGNATURES = {"C": [], "G": ["F"], "D": ["F", "C"], "A": ["F", "C",
"G"], "E": ["F", "C", "G", "D"], "B": ["F", "C", "G", "D", "A"], "F#":
["F", "C", "G", "D", "A", "E"], "C#": ["F", "C", "G", "D", "A", "E", "B"],
"F": ["B"], "Bb": ["B", "E"], "Eb": ["B", "E", "A"], "Ab": ["B", "E", "A",
"D"], "Db": ["B", "E", "A", "D", "G"], "Gb": ["B", "E", "A", "D", "G",
"C"], "Cb": ["B", "E", "A", "D", "G", "C", "F"], "Ahm": [], "Ehm": ["F"],
"Bhm": ["F", "C"], "F#hm": ["F", "C", "G"], "C#hm": ["F", "C", "G", "D"],
"G#hm": ["F", "C", "G", "D", "A"], "D#hm": ["F", "C", "G", "D", "A", "E"],
"A#hm": ["F", "C", "G", "D", "A", "E", "B"], "Dhm": ["B"], "Ghm": ["B",
"E"], "Chm": ["B", "E", "A"], "Fhm": ["B", "E", "A", "D"], "Bbhm": ["B",
"E", "A", "D", "G"], "Ebhm": ["B", "E", "A", "D", "G", "C"], "Abhm": ["B",
"E", "A", "D", "G", "C", "F"], "Amm": [], "Emm": ["F"], "Bmm": ["F", "C"],
"F#mm": ["F", "C", "G"], "C#mm": ["F", "C", "G", "D"], "G#mm": ["F", "C",
"G", "D", "A"], "D#mm": ["F", "C", "G", "D", "A", "E"], "A#mm": ["F", "C",
"G", "D", "A", "E", "B"], "Dmm": ["B"], "Gmm": ["B", "E"], "Cmm": ["B",
"E", "A"], "Fmm": ["B", "E", "A", "D"], "Bbmm": ["B", "E", "A", "D", "G"],
"Ebmm": ["B", "E", "A", "D", "G", "C"], "Abmm": ["B", "E", "A", "D", "G",
"C", "F"]}
now in the functions when ever I need to access i just use it.
eg:
sharps_or_flats = KEY_SIGNATURES[key]
or I can create it like this
class Variables():
def __init__(self, adv):
self.choice = choice # level of advancement in questions
self.mousepos = (SCREENW / 2, SCREENH / 2)
self.SCREEN = pygame.display.get_surface()
self.KEY_SIGNATURES = {"C": [], "G": ["F"], "D":
["F", "C"], "A": ["F", "C", "G"], "E": ["F", "C", "G", "D"], "B": ["F",
"C", "G", "D", "A"], "F#": ["F", "C", "G", "D", "A", "E"], "C#": ["F", "C",
"G", "D", "A", "E", "B"], "F": ["B"], "Bb": ["B", "E"], "Eb": ["B", "E",
"A"], "Ab": ["B", "E", "A", "D"], "Db": ["B", "E", "A", "D", "G"], "Gb":
["B", "E", "A", "D", "G", "C"], "Cb": ["B", "E", "A", "D", "G", "C", "F"],
"Ahm": [], "Ehm": ["F"], "Bhm": ["F", "C"], "F#hm": ["F", "C", "G"],
"C#hm": ["F", "C", "G", "D"], "G#hm": ["F", "C", "G", "D", "A"], "D#hm":
["F", "C", "G", "D", "A", "E"], "A#hm": ["F", "C", "G", "D", "A", "E",
"B"], "Dhm": ["B"], "Ghm": ["B", "E"], "Chm": ["B", "E", "A"], "Fhm": ["B",
"E", "A", "D"], "Bbhm": ["B", "E", "A", "D", "G"], "Ebhm": ["B", "E", "A",
"D", "G", "C"], "Abhm": ["B", "E", "A", "D", "G", "C", "F"], "Amm": [],
"Emm": ["F"], "Bmm": ["F", "C"], "F#mm": ["F", "C", "G"], "C#mm": ["F",
"C", "G", "D"], "G#mm": ["F", "C", "G", "D", "A"], "D#mm": ["F", "C", "G",
"D", "A", "E"], "A#mm": ["F", "C", "G", "D", "A", "E", "B"], "Dmm": ["B"],
"Gmm": ["B", "E"], "Cmm": ["B", "E", "A"], "Fmm": ["B", "E", "A", "D"],
"Bbmm": ["B", "E", "A", "D", "G"], "Ebmm": ["B", "E", "A", "D", "G", "C"],
"Abmm": ["B", "E", "A", "D", "G", "C", "F"]}
now I call the class with
v=Variables()
now the same dict is
v.Key_SIGNATURES
sharps_or_flats = v.KEY_SIGNATURES[key]
my questions:
which is better to use and why?
Do both remain in memory(separately of course) till I exit the program once
I run it?
Will memory usage be the same?
will the creation of the dict take the same time in both above?
On Fri, Jun 13, 2014 at 10:44 PM, Albert-Jan Roskam <
fomcl at yahoo.com.dmarc.invalid> wrote:
>
>
> ----- Original Message -----
>
> > From: Steven D'Aprano <steve at pearwood.info>
> > To: tutor at 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
>
> _______________________________________________
> Tutor maillist - Tutor at python.org
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>
--
Diliup Gabadamudalige
http://www.diliupg.com
http://soft.diliupg.com/
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