Choose random seed and save it

Question

I would like to choose a random seed for numpy.random and save it to a variable. I can set the seed using numpy.random.seed(seed=None) but how do you

Answer 1

The full state of the MT19937 PRNG that underlies RandomState cannot be contained in a single (normally-sized, e.g. 32-bit or 64-bit) integer. It has an array of 624 32-bit integers for its state. Seeding with an integer actually runs a smaller, simpler PRNG to generate those 624 words. It is just a convenient way for humans to manually set the state of the PRNG to a state that can be consistently replicated. But most states that the PRNG gets into cannot be reduced back to a convenient 32-bit integer. That initializer PRNG cannot work "backwards" in this way. Instead, the whole state of RandomState is contained in that 624-entry array. You can get this array and set it using the get_state() and set_state() methods.

>>> import numpy as np
>>> prng = np.random.RandomState()
>>> state = prng.get_state()
>>> state
('MT19937',
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        497650124, 3782308076, 4180165271, 3190969185, 1284472452, 2868357773, 1148940887,  433865334,  643839653, 3091921054, 2157305915, 4079505239,
       1396964105,  221256094, 2789328727, 3216471912, 1782932723, 1704818545, 3880597634, 2060476197, 2599008138, 1389874875,   56765165, 1173841349,
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        922778621, 1805422791, 3344418665, 1738799711, 1367565729,   34977430, 4008589298, 2239856842, 1717530303,   32049105, 3468621644, 2269299060,
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       2961031222, 1709451377,  134371222, 4217784577, 3792528752, 1278543741,  291978547, 1987232116, 2685749450,  948431490, 3550698848, 1384058130,
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       3762934166, 3303914085, 1910775932, 2241726842, 3836262483,  905479357, 2974032168, 3187395363, 3071243546, 3571439927, 3756380578,   53494506,
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        153287562, 2302436235, 3852961194, 2073555800, 3034065218, 1997718747, 3343015031, 3198064720, 4286393046, 3338997777, 1383744819, 1553624825,
       1183357509, 1141531260,   25823987, 2951322047, 4066666075, 3687780778, 3680053857,  478734258, 3674686218, 1457141125, 3673486342, 3224971043,
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       1457126476, 3694269669, 4248613755, 3161380741, 3396304589,   26218095, 4262314194, 3090365505, 2603976562, 1742639443, 3357356842, 2527908520,
       2744118109,  764708873,  608716002,  218517036, 2028062957,  123264851, 3930797933, 1358280349, 3770182726, 1475205800, 4083653367,  728440387,
        578359463, 3792859449, 2660424205,  866268419, 2680711984, 1892477918, 3473675890,    5948212,  590585309, 1434154869, 4019090587, 3447601971,
       3777365598,  502271900,  933280098,  551410763, 4178545332, 2426657681,  435161245,  103552671, 2751130089, 1664159723, 2124278140, 3518289293,
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       4133763948, 2773874577,  459104952, 3336058631,  791669682,   79496438, 1268256964, 1327605157, 3196785479, 3094404795, 3971934915,  967528556,
       1680157581, 1508139540, 3821158380, 3603819236,  593155253, 1875654417, 3734837198, 3315972391, 2450938455, 1863178045,  619766009, 1376779265,
        843230528, 1818810226, 1508689309, 1353144904, 3459699509,  734863896, 1593154156, 4178196553,  559982910, 1937392142, 3328058492, 2417976146,
       3197182411, 2233439700,  196920494, 3714701774, 4104568606,  850977604,  382851029, 4143478133, 3024891142, 2455897904,   28681198, 3438784382,
        578301023, 2215641381,   59642080, 2913625733, 2063824530, 2113835214,  563503294, 2261300428, 1156324177, 3080988993, 1485826140,  291045970,
       3740234437, 2802003429,  804278225, 1715783317, 3683156408, 2855890524, 2390104305,  172369852, 3358371994, 1184782876, 2087670358,  840924195,
       2727925375, 1806621317, 2785628046, 4163132724, 3580142689, 1107366902,  809125531, 3131770778, 1922818283,  888842000, 2875999147, 2752567229,
        170460348, 1952532683, 1705378473, 1784443344, 1111435234, 2373828316, 1440965774, 3986117425,  849160375, 1233392480, 4073490673, 3948548975,
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       3414530672, 2739562683,  670592573, 3517927973, 3902124497, 4085960935,  823980090,  982263838, 1807290575, 1182843877, 3543714667, 1403590968,
        329717243, 1055811172, 3550329386, 3998515559, 3251582755, 2201054306, 3347834116, 1211790680,   62972368,   88227180, 2967020240, 1937245345,
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       3025460765, 1087397787, 1520908724, 3979084899, 3800423495,  139799221,  644687977, 1080267251,  599331265,  379370383, 3716980301, 2450151406,
       1223752702,  300351842,  295249068, 1870733374, 2986315084, 1323736886,  306347366, 2697516131, 3896227616, 2556699990,  578928278, 2356101730,
        171880210,  722319049,  740054230, 3855145369, 1468149367,  311954206, 4099077708, 2941657479,  119786529, 3197372768, 2115311247, 2469241538,
       2636086203, 2206369175,  374899905, 3730393440, 2288141890,  719446033, 4096038147, 4294410470,   19272682, 1964868281, 3192582061, 3934009074,
       1135732985,  682697379, 3290113635, 1489105351,  347638343,  147496092, 4175447059,  341595821, 3117140389, 1003085251, 1889252416,  913732530,
       3459561042, 3662473182, 3839509269, 1519115576,     677113,  597583022, 3031451769,  607339281,   55523370, 2676982537, 1238056185, 1550912054,
       3112284354, 1345961520, 1541909925, 3726796822, 2696250478, 3254836471, 1362613883, 3129122359, 1550126204,  129690651, 2386622242,  407302605,
       1753882614, 2376840660, 1076064874, 2449053256, 3162294193, 3779999195, 3925427556, 2601606505, 1901788890, 2217639773,  406665902, 3640687773,
       2061876750,  968895635,  587973195, 2778479214,  668417883, 2226398520, 1464491431, 2792659882, 3481258691, 2339776369, 2747947338, 3000199533,
       3712567952,  376206272, 2149616269,  985682501,  865295391, 1812641626,  567425379, 1468520640, 2273677177, 2267568076, 3898328230,  898149034,
       3750298043,  394538907, 4101461357, 2781824777, 2719406676, 3415420393,  122661889, 1452536307, 1463257506, 2874481787, 2250093815, 1439068642,
        597070280, 1439076517, 4207797347, 2579732532, 3704826787, 3847236064, 4155289003,  990963026, 2602619627,  701644802, 3629646548, 1110000288,
       3609356614, 2748019645,  638526248, 3265491895, 2839687161,  913026615, 2748040592,  975131382,   83378202, 4236013846,  764917668, 1887262417], dtype=uint32),
 624,
 0,
 0.0)
>>> prng.random_sample()
0.20598058788141316
>>> prng.random_sample()
0.6864005375257146
>>> prng.random_sample()
0.08407651896523582
>>> prng.set_state(state)
>>> prng.random_sample()
0.20598058788141316
>>> prng.random_sample()
0.6864005375257146

You can also pickle RandomState objects. We implemented this using the get_state() data, so it will reliably reproduce the state of the PRNG. Depending on exactly what you want to do (you don't say), this is frequently the most convenient thing to do rather than mucking about with get_state() and set_state() manually.

>>> import cPickle
>>> pickled = cPickle.dumps(prng)
>>> prng.random_sample()
0.08407651896523582
>>> prng.random_sample()
0.3501860271954601
>>> prng2 = cPickle.loads(pickled)
>>> prng2.random_sample()
0.08407651896523582
>>> prng2.random_sample()
0.3501860271954601