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bpo-37691: Let math.dist() accept sequences and iterables for coordinates #14975

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Merged
merged 7 commits into from
Jul 27, 2019
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bpo-37691: Let math.dist() accept sequences and iterables for coordinates #14975

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74f78d2
Allow sequence arguments to math_dist()
rhettinger Jul 26, 2019
634c470
Update the argument clinic
rhettinger Jul 27, 2019
a9e3d42
Update tests
rhettinger Jul 27, 2019
3b18d77
Update the argument clinic
rhettinger Jul 27, 2019
2c341ca
Update the documentation
rhettinger Jul 27, 2019
95df88c
Add blurb
rhettinger Jul 27, 2019
4303073
Restore assertions
rhettinger Jul 27, 2019
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3 changes: 2 additions & 1 deletion Doc/library/math.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -400,7 +400,8 @@ Trigonometric functions
.. function:: dist(p, q)

Return the Euclidean distance between two points *p* and *q*, each
given as a tuple of coordinates. The two tuples must be the same size.
given as a sequence (or iterable) of coordinates. The two points
must have the same dimension.

Roughly equivalent to::

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6 changes: 4 additions & 2 deletions Lib/test/test_math.py
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Expand Up @@ -833,6 +833,10 @@ def testDist(self):
sqrt(sum((px - qx) ** 2.0 for px, qx in zip(p, q)))
)

# Test non-tuple inputs
self.assertEqual(dist([1.0, 2.0, 3.0], [4.0, 2.0, -1.0]), 5.0)
self.assertEqual(dist(iter([1.0, 2.0, 3.0]), iter([4.0, 2.0, -1.0])), 5.0)

# Test allowable types (those with __float__)
self.assertEqual(dist((14.0, 1.0), (2.0, -4.0)), 13.0)
self.assertEqual(dist((14, 1), (2, -4)), 13)
Expand Down Expand Up @@ -873,8 +877,6 @@ class T(tuple):
dist((1, 2, 3), (4, 5, 6), (7, 8, 9))
with self.assertRaises(TypeError): # Scalars not allowed
dist(1, 2)
with self.assertRaises(TypeError): # Lists not allowed
dist([1, 2, 3], [4, 5, 6])
with self.assertRaises(TypeError): # Reject values without __float__
dist((1.1, 'string', 2.2), (1, 2, 3))
with self.assertRaises(ValueError): # Check dimension agree
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2019-07-26-22-30-01.bpo-37691.1Li3rx.rst
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@@ -0,0 +1,2 @@
Let math.dist() accept coordinates as sequences (or iterables) rather than
just tuples.
14 changes: 3 additions & 11 deletions Modules/clinic/mathmodule.c.h
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42 changes: 36 additions & 6 deletions Modules/mathmodule.c
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Expand Up @@ -2427,31 +2427,49 @@ vector_norm(Py_ssize_t n, double *vec, double max, int found_nan)
/*[clinic input]
math.dist

p: object(subclass_of='&PyTuple_Type')
q: object(subclass_of='&PyTuple_Type')
p: object
q: object
/

Return the Euclidean distance between two points p and q.

The points should be specified as tuples of coordinates.
Both tuples must be the same size.
The points should be specified as sequences (or iterables) of
coordinates. Both inputs must have the same dimension.

Roughly equivalent to:
sqrt(sum((px - qx) ** 2.0 for px, qx in zip(p, q)))
[clinic start generated code]*/

static PyObject *
math_dist_impl(PyObject *module, PyObject *p, PyObject *q)
/*[clinic end generated code: output=56bd9538d06bbcfe input=937122eaa5f19272]*/
/*[clinic end generated code: output=56bd9538d06bbcfe input=74e85e1b6092e68e]*/
{
PyObject *item;
double max = 0.0;
double x, px, qx, result;
Py_ssize_t i, m, n;
int found_nan = 0;
int found_nan = 0, p_allocated = 0, q_allocated = 0;
double diffs_on_stack[NUM_STACK_ELEMS];
double *diffs = diffs_on_stack;

if (!PyTuple_Check(p)) {
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Why not call just PySequence_Tuple() (which is a no-op for tuples)? This would simplify the setup and the cleanup code.

It may be also worth to use PySequence_Fast() and PySequence_Fast_GET_ITEM() in the loop. This will save you allocating a new tuple. For general iterable PySequence_Tuple() creates a list and a tuple, but PySequence_Fast() creates just a list.

But you will need to call PySequence_Fast_GET_SIZE() in a loop because list's size can be changed when you convert items to the C double.

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@rhettinger rhettinger Jul 27, 2019 •
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I didn't want any external function calls on the fast path for the common case.

I did try it out. The patch was shorter but it caused a 15% performance degradation:

# baseline
$ pytime -r11 -s 'from math import dist' 'dist((10.5, 12.5), (13.5, 8.5))'
5000000 loops, best of 11: 57.3 nsec per loop

# patched to always call PySequence_Tuple() and always Py_DECREF on exit
$ pytime -r11 -s 'from math import dist' -s 'p, q = (10.5, 12.5), (13.5, 8.5)' 'dist(p, q)'
5000000 loops, best of 11: 64.7 nsec per loop

p = PySequence_Tuple(p);
if (p == NULL) {
return NULL;
}
p_allocated = 1;
}
if (!PyTuple_Check(q)) {
q = PySequence_Tuple(q);
if (q == NULL) {
if (p_allocated) {
Py_DECREF(p);
}
return NULL;
}
q_allocated = 1;
}

m = PyTuple_GET_SIZE(p);
n = PyTuple_GET_SIZE(q);
if (m != n) {
Expand Down Expand Up @@ -2482,12 +2500,24 @@ math_dist_impl(PyObject *module, PyObject *p, PyObject *q)
if (diffs != diffs_on_stack) {
PyObject_Free(diffs);
}
if (p_allocated) {
Py_DECREF(p);
}
if (q_allocated) {
Py_DECREF(q);
}
return PyFloat_FromDouble(result);

error_exit:
if (diffs != diffs_on_stack) {
PyObject_Free(diffs);
}
if (p_allocated) {
Py_DECREF(p);
}
if (q_allocated) {
Py_DECREF(q);
}
return NULL;
}

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