ENH: np.random.default_gen()

doc/source/reference/random/generator.rst

@@ -12,6 +12,8 @@ random values from useful distributions. The default BitGenerator used by
 can be changed by passing an instantized BitGenerator to ``Generator``.
 
 
+.. autofunction:: default_gen
+
 .. autoclass:: Generator
 	:exclude-members:
 

doc/source/reference/random/index.rst

@@ -48,9 +48,10 @@ the random values are generated by `~.PCG64`. The
 
 .. code-block:: python
 
-  # As replacement for RandomState()
-  from numpy.random import Generator
-  rg = Generator()
+  # As replacement for RandomState(); default_gen() instantiates Generator with
+  # the default PCG64 BitGenerator.
+  from numpy.random import default_gen
+  rg = default_gen()
   rg.standard_normal()
   rg.bit_generator
 

doc/source/reference/random/new-or-different.rst

@@ -19,15 +19,15 @@ Quick comparison of legacy `mtrand <legacy>`_ to the new `Generator`
 ================== ==================== =============
 Feature            Older Equivalent     Notes
 ------------------ -------------------- -------------
-`Generator`        `RandomState`        ``Generator`` requires a stream
+`~.Generator`      `~.RandomState`      ``Generator`` requires a stream
                                         source, called a `BitGenerator
                                         <bit_generators>` A number of these
                                         are provided.  ``RandomState`` uses
-                                        only the Box- Muller method.
+                                        only the Mersenne Twister.
 ------------------ -------------------- -------------
-``np.random.``     ``np.random.``       Access the values in a BitGenerator,
-``Generator().``   ``random_sample()``  convert them to ``float64`` in the
-``random()``                            interval ``[0.0.,`` `` 1.0)``.
+``random``         ``random_sample``    Access the values in a BitGenerator,
+                                        convert them to ``float64`` in the
+                                        interval ``[0.0.,`` `` 1.0)``.
                                         In addition to the ``size`` kwarg, now
                                         supports ``dtype='d'`` or ``dtype='f'``,
                                         and an ``out`` kwarg to fill a user-
@@ -36,8 +36,8 @@ Feature            Older Equivalent     Notes
                                         Many other distributions are also
                                         supported.
 ------------------ -------------------- -------------
-``Generator().``   ``randint``,         Use the ``endpoint`` kwarg to adjust
-``integers()``     ``random_integers``  the inclusion or exclution of the
+``integers``       ``randint``,         Use the ``endpoint`` kwarg to adjust
+                   ``random_integers``  the inclusion or exclution of the
                                         ``high`` interval endpoint
 ================== ==================== =============
 
@@ -56,7 +56,7 @@ And in more detail:
   random numbers from a discrete uniform distribution. The ``rand`` and
   ``randn`` methods are only available through the legacy `~.RandomState`.
   This replaces both ``randint`` and the deprecated ``random_integers``.
-* The Box-Muller used to produce NumPy's normals is no longer available.
+* The Box-Muller method used to produce NumPy's normals is no longer available.
 * All bit generators can produce doubles, uint64s and
   uint32s via CTypes (`~PCG64.ctypes`) and CFFI (`~PCG64.cffi`).
   This allows these bit generators to be used in numba.

numpy/random/__init__.py

@@ -3,16 +3,42 @@
 Random Number Generation
 ========================
 
-Instantiate a BitGenerator and wrap it in a Generator
-which will convert the uniform stream to a number of distributions. The "bare"
-functions are kept for legacy code, they should be called with the newer API
-via ``np.random.Generator().function`` instead
+Use ``default_gen()`` to create a `Generator` and call its methods.
+
+=============== =========================================================
+Generator
+--------------- ---------------------------------------------------------
+Generator       Class implementing all of the random number distributions
+default_gen     Default constructor for ``Generator``
+=============== =========================================================
+
+============================================= ===
+BitGenerator Streams that work with Generator
+--------------------------------------------- ---
+MT19937
+PCG64
+Philox
+SFC64
+============================================= ===
+
+============================================= ===
+Getting entropy to initialize a BitGenerator
+--------------------------------------------- ---
+SeedSequence
+============================================= ===
+
+
+Legacy
+------
+
+For backwards compatibility with previous versions of numpy before 1.17, the
+various aliases to the global `RandomState` methods are left alone and do not
+use the new `Generator` API.
 
 ==================== =========================================================
 Utility functions
 -------------------- ---------------------------------------------------------
 random               Uniformly distributed floats over ``[0, 1)``
-integers             Uniformly distributed integers, replaces ``randint``
 bytes                Uniformly distributed random bytes.
 permutation          Randomly permute a sequence / generate a random sequence.
 shuffle              Randomly permute a sequence in place.
@@ -94,20 +120,6 @@
 set_state            Set state of generator.
 ==================== =========================================================
 
-============================================= ===
-BitGenerator Streams that work with Generator
---------------------------------------------- ---
-MT19937
-PCG64
-Philox
-SFC64
-============================================= ===
-
-============================================= ===
-Getting entropy to initialize a BitGenerator
---------------------------------------------- ---
-SeedSequence
-============================================= ===
 
 """
 from __future__ import division, absolute_import, print_function
@@ -167,7 +179,7 @@
 
 from . import mtrand
 from .mtrand import *
-from .generator import Generator
+from .generator import Generator, default_gen
 from .bit_generator import SeedSequence
 from .mt19937 import MT19937
 from .pcg64 import PCG64
@@ -176,7 +188,7 @@
 from .mtrand import RandomState
 
 __all__ += ['Generator', 'RandomState', 'SeedSequence', 'MT19937',
-            'Philox', 'PCG64', 'SFC64']
+            'Philox', 'PCG64', 'SFC64', 'default_gen']
 
 
 def __RandomState_ctor():

numpy/random/bit_generator.pxd

@@ -13,7 +13,6 @@ cdef class BitGenerator():
 
 cdef class SeedSequence():
     cdef readonly object entropy
-    cdef readonly object program_entropy
     cdef readonly tuple spawn_key
     cdef readonly int pool_size
     cdef readonly object pool

numpy/random/bit_generator.pyx

@@ -116,7 +116,7 @@ def _coerce_to_uint32_array(x):
     Examples
     --------
     >>> import numpy as np
-    >>> from seed_seq import _coerce_to_uint32_array
+    >>> from np.random.bit_generator import _coerce_to_uint32_array
     >>> _coerce_to_uint32_array(12345)
     array([12345], dtype=uint32)
     >>> _coerce_to_uint32_array('12345')
@@ -473,17 +473,20 @@ ISpawnableSeedSequence.register(SeedSequence)
 
 cdef class BitGenerator():
     """
-    BitGenerator(seed_seq=None)
+    BitGenerator(seed=None)
 
     Base Class for generic BitGenerators, which provide a stream
     of random bits based on different algorithms. Must be overridden.
 
     Parameters
     ----------
-    seed_seq : {None, ISeedSequence, int, sequence[int]}, optional
-        A ISeedSequence to initialize the BitGenerator. If None, one will be
-        created. If an int or a sequence of ints, it will be used as the
-        entropy for creating a SeedSequence.
+    seed : {None, int, array_like[ints], ISeedSequence}, optional
+        A seed to initialize the `BitGenerator`. If None, then fresh,
+        unpredictable entropy will be pulled from the OS. If an ``int`` or
+        ``array_like[ints]`` is passed, then it will be passed to
+        `SeedSequence` to derive the initial `BitGenerator` state. One may also
+        pass in an implementor of the `ISeedSequence` interface like
+        `SeedSequence`.
 
     Attributes
     ----------
@@ -498,7 +501,7 @@ cdef class BitGenerator():
     SeedSequence
     """
 
-    def __init__(self, seed_seq=None):
+    def __init__(self, seed=None):
         self.lock = Lock()
         self._bitgen.state = <void *>0
         if type(self) is BitGenerator:
@@ -509,9 +512,9 @@ cdef class BitGenerator():
 
         cdef const char *name = "BitGenerator"
         self.capsule = PyCapsule_New(<void *>&self._bitgen, name, NULL)
-        if not isinstance(seed_seq, ISeedSequence):
-            seed_seq = SeedSequence(seed_seq)
-        self._seed_seq = seed_seq
+        if not isinstance(seed, ISeedSequence):
+            seed = SeedSequence(seed)
+        self._seed_seq = seed
 
     # Pickling support:
     def __getstate__(self):