Convenience class for doing maths with explicit coordinates
Project description
coordinates
Convenience class for dealing with coordinates which need both maths and explicit ordering.
Motivation
Numpy arrays are great for doing maths with coordinates stored as arrays.
Dicts are great for dealing with coordinate systems where the order keeps changing (e.g. between C and Fortran order).
But what if you want both?
(Note: if you're doing lots of maths... stick with numpy
)
Installation
pip install coordinates
Usage
Coordinate
s are Mapping
s (i.e. dict
like). They don't expose an interface for mutation, but
we're all consenting adults so if you really want to modify the internal _dict
, I won't
stop you.
Instantiation
They can be instantiated in any of the ways a dict
can (from another Mapping
, a sequence of pairs,
some keyword arguments, or a mixture of the above).
from coordinates import Coordinate
Coordinate({'x': 1, 'y': 2})
Coordinate({'x': 1}, y=2)
Coordinate([('x', 1), ('y', 2)])
Coordinate(x=1, y=2)
If an order is defined (more on this later), you can also instantiate a Coordinate
from a single
argument which is a sequence, or from a number of *args
.
Coordinate([1, 2], order='xy')
Coordinate(1, 2, order='xy')
Coordinate.default_order = 'xy'
Coordinate([1, 2])
Coordinate(1, 2)
Because Mapping
s can be instantiated from other Mapping
s, you can "extend" existing coordinates
into new dimensions.
coord_2d = Coordinate(x=1, y=2)
coord_3d = Coordinate(coord_2d, z=3)
Finally, many Coordinate
s can be instantiated lazily using from_sequence
:
Coordinate.from_sequence([(1, 2, 3), (3, 4, 5)], order='xyz')
Coordinate.from_sequence([{'x': 1, 'y': 2}, {'x': 3, 'y': 4}], z=10)
To note:
order
dependent instantiation is incompatible with**kwargs
 Instantiation from a sequence of tuples will fail in 2D because it will be interpreted as
keyvalue pairs. Use a comprehension here instead:
Coordinate.from_sequence(zip('xy', row) for row in sequence)
Maths
Coordinates do maths like you might expect them to, where the other operand is anything dictlike with the same keys, or a number.
coord = Coordinate(x=1, y=2, z=3)
coord * 2 == Coordinate(x=2, y=4, z=6)
>>> True
coord ** 2 == Coordinate(x=1, y=4, z=9)
>>> True
coord + coord == Coordinate(x=2, y=4, z=3)
>>> True
coord += 1 # coord is a reference to a new object; no mutation
coord == Coordinate(x=2, y=3, z=4)
>>> True
abs(Coordinate(x=10, y=10)) == Coordinate(x=10, y=10)
>>> True
import math
math.ceil(Coordinate(x=0.5)) == Coordinate(x=1)
>>> True
math.floor(Coordinate(x=0.5)) == Coordinate(x=0)
>>> True
They also have some convenience methods for getting the sum, product or norm of their keys.
coord.sum() == 9
>>> True
coord.prod() == 24
>>> True
Coordinate(x=3, y=4).norm(order=2) == 5
>>> True
Ordering
You can get the keys, values or items of the Coordinate
in a specific order:
coord.to_list('yxz') == [2, 1, 3]
>>> True
list(coord.items('yxz')) == [('y', 2), ('x', 1), ('z', 3)]
>>> True
The default order for a single instance can be given on instantiation, or mutated (this does not affect equality).
The default order for all Coordinate
s can be set on the class. This affects existing instances, but does not
override their order if it was set explicitly.
If neither an instance order
or a class default_order
is set, it falls back to reverse lexicographic.
coord3 = Coordinate(x=1, y=2, z=3, order='zxy')
coord3.order = 'yzx'
Coordinate.default_order = 'xyz'
Subclassing
If you're working in one space, the spaced_coordinate
factory can create custom subclasses with a fixed set of
keys and optionally a default order.
from coordinates import spaced_coordinate
CoordinateXYZC = spaced_coordinate('CoordinateXYZC', 'xyzc')
# this will raise a ValueError
CoordinateXYZC(x=1, y=2, z=3)
Or you can subclass Coordinate
directly.
Value access
Coordinate values can be accessed with dictlike syntax (coord['x']
, coord.get('y', 2)
) or, for convenience,
attributelike (coord.z
) if the keys are strings.
Note
If you don't want the orderrelated functionality for another application, the base class MathDict
is
implemented here too.
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