bpo-36018: Address more reviewer feedback (GH-15733)
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@ -514,15 +514,14 @@ However, for reading convenience, most of the examples show sorted sequences.
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Set *n* to 4 for quartiles (the default). Set *n* to 10 for deciles. Set
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*n* to 100 for percentiles which gives the 99 cuts points that separate
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*data* in to 100 equal sized groups. Raises :exc:`StatisticsError` if *n*
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*data* into 100 equal sized groups. Raises :exc:`StatisticsError` if *n*
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is not least 1.
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The *data* can be any iterable containing sample data or it can be an
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instance of a class that defines an :meth:`~inv_cdf` method. For meaningful
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The *data* can be any iterable containing sample data. For meaningful
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results, the number of data points in *data* should be larger than *n*.
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Raises :exc:`StatisticsError` if there are not at least two data points.
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For sample data, the cut points are linearly interpolated from the
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The cut points are linearly interpolated from the
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two nearest data points. For example, if a cut point falls one-third
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of the distance between two sample values, ``100`` and ``112``, the
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cut-point will evaluate to ``104``.
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@ -547,9 +546,6 @@ However, for reading convenience, most of the examples show sorted sequences.
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values, the method sorts them and assigns the following percentiles:
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0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%.
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If *data* is an instance of a class that defines an
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:meth:`~inv_cdf` method, setting *method* has no effect.
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.. doctest::
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# Decile cut points for empirically sampled data
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@ -561,11 +557,6 @@ However, for reading convenience, most of the examples show sorted sequences.
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>>> [round(q, 1) for q in quantiles(data, n=10)]
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[81.0, 86.2, 89.0, 99.4, 102.5, 103.6, 106.0, 109.8, 111.0]
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>>> # Quartile cut points for the standard normal distribution
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>>> Z = NormalDist()
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>>> [round(q, 4) for q in quantiles(Z, n=4)]
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[-0.6745, 0.0, 0.6745]
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.. versionadded:: 3.8
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@ -607,6 +598,18 @@ of applications in statistics.
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<https://en.wikipedia.org/wiki/Arithmetic_mean>`_ of a normal
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distribution.
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.. attribute:: median
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A read-only property for the `median
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<https://en.wikipedia.org/wiki/Median>`_ of a normal
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distribution.
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.. attribute:: mode
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A read-only property for the `mode
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<https://en.wikipedia.org/wiki/Mode_(statistics)>`_ of a normal
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distribution.
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.. attribute:: stdev
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A read-only property for the `standard deviation
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@ -678,6 +681,16 @@ of applications in statistics.
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the two probability density functions
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<https://www.rasch.org/rmt/rmt101r.htm>`_.
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.. method:: NormalDist.quantiles()
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Divide the normal distribution into *n* continuous intervals with
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equal probability. Returns a list of (n - 1) cut points separating
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the intervals.
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Set *n* to 4 for quartiles (the default). Set *n* to 10 for deciles.
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Set *n* to 100 for percentiles which gives the 99 cuts points that
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separate the normal distribution into 100 equal sized groups.
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Instances of :class:`NormalDist` support addition, subtraction,
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multiplication and division by a constant. These operations
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are used for translation and scaling. For example:
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@ -733,9 +746,9 @@ Find the `quartiles <https://en.wikipedia.org/wiki/Quartile>`_ and `deciles
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.. doctest::
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>>> list(map(round, quantiles(sat)))
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>>> list(map(round, sat.quantiles()))
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[928, 1060, 1192]
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>>> list(map(round, quantiles(sat, n=10)))
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>>> list(map(round, sat.quantiles(n=10)))
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[810, 896, 958, 1011, 1060, 1109, 1162, 1224, 1310]
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To estimate the distribution for a model than isn't easy to solve
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@ -624,9 +624,8 @@ def quantiles(data, /, *, n=4, method='exclusive'):
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Set *n* to 100 for percentiles which gives the 99 cuts points that
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separate *data* in to 100 equal sized groups.
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The *data* can be any iterable containing sample data or it can be
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an instance of a class that defines an inv_cdf() method. For sample
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data, the cut points are linearly interpolated between data points.
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The *data* can be any iterable containing sample.
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The cut points are linearly interpolated between data points.
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If *method* is set to *inclusive*, *data* is treated as population
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data. The minimum value is treated as the 0th percentile and the
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@ -634,8 +633,6 @@ def quantiles(data, /, *, n=4, method='exclusive'):
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"""
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if n < 1:
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raise StatisticsError('n must be at least 1')
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if hasattr(data, 'inv_cdf'):
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return [data.inv_cdf(i / n) for i in range(1, n)]
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data = sorted(data)
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ld = len(data)
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if ld < 2:
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@ -955,6 +952,17 @@ class NormalDist:
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raise StatisticsError('cdf() not defined when sigma at or below zero')
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return _normal_dist_inv_cdf(p, self._mu, self._sigma)
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def quantiles(self, n=4):
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"""Divide into *n* continuous intervals with equal probability.
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Returns a list of (n - 1) cut points separating the intervals.
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Set *n* to 4 for quartiles (the default). Set *n* to 10 for deciles.
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Set *n* to 100 for percentiles which gives the 99 cuts points that
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separate the normal distribution in to 100 equal sized groups.
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"""
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return [self.inv_cdf(i / n) for i in range(1, n)]
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def overlap(self, other):
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"""Compute the overlapping coefficient (OVL) between two normal distributions.
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@ -994,6 +1002,20 @@ class NormalDist:
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"Arithmetic mean of the normal distribution."
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return self._mu
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@property
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def median(self):
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"Return the median of the normal distribution"
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return self._mu
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@property
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def mode(self):
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"""Return the mode of the normal distribution
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The mode is the value x where which the probability density
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function (pdf) takes its maximum value.
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"""
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return self._mu
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@property
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def stdev(self):
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"Standard deviation of the normal distribution."
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@ -2198,16 +2198,6 @@ class TestQuantiles(unittest.TestCase):
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exp = list(map(f, expected))
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act = quantiles(map(f, data), n=n)
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self.assertTrue(all(math.isclose(e, a) for e, a in zip(exp, act)))
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# Quartiles of a standard normal distribution
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for n, expected in [
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(1, []),
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(2, [0.0]),
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(3, [-0.4307, 0.4307]),
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(4 ,[-0.6745, 0.0, 0.6745]),
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]:
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actual = quantiles(statistics.NormalDist(), n=n)
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self.assertTrue(all(math.isclose(e, a, abs_tol=0.0001)
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for e, a in zip(expected, actual)))
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# Q2 agrees with median()
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for k in range(2, 60):
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data = random.choices(range(100), k=k)
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@ -2248,16 +2238,6 @@ class TestQuantiles(unittest.TestCase):
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exp = list(map(f, expected))
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act = quantiles(map(f, data), n=n, method="inclusive")
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self.assertTrue(all(math.isclose(e, a) for e, a in zip(exp, act)))
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# Quartiles of a standard normal distribution
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for n, expected in [
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(1, []),
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(2, [0.0]),
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(3, [-0.4307, 0.4307]),
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(4 ,[-0.6745, 0.0, 0.6745]),
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]:
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actual = quantiles(statistics.NormalDist(), n=n, method="inclusive")
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self.assertTrue(all(math.isclose(e, a, abs_tol=0.0001)
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for e, a in zip(expected, actual)))
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# Natural deciles
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self.assertEqual(quantiles([0, 100], n=10, method='inclusive'),
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[10.0, 20.0, 30.0, 40.0, 50.0, 60.0, 70.0, 80.0, 90.0])
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@ -2546,6 +2526,19 @@ class TestNormalDist:
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# Special values
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self.assertTrue(math.isnan(Z.inv_cdf(float('NaN'))))
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def test_quantiles(self):
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# Quartiles of a standard normal distribution
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Z = self.module.NormalDist()
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for n, expected in [
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(1, []),
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(2, [0.0]),
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(3, [-0.4307, 0.4307]),
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(4 ,[-0.6745, 0.0, 0.6745]),
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]:
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actual = Z.quantiles(n=n)
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self.assertTrue(all(math.isclose(e, a, abs_tol=0.0001)
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for e, a in zip(expected, actual)))
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def test_overlap(self):
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NormalDist = self.module.NormalDist
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@ -2612,6 +2605,8 @@ class TestNormalDist:
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def test_properties(self):
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X = self.module.NormalDist(100, 15)
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self.assertEqual(X.mean, 100)
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self.assertEqual(X.median, 100)
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self.assertEqual(X.mode, 100)
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self.assertEqual(X.stdev, 15)
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self.assertEqual(X.variance, 225)
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