#!/usr/bin/env python
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"""Module for helping to create Iris constraints."""
import iris
[docs]def create_sorted_lambda_constraint(coord_name, values, tolerance=1.0E-7):
"""
Create a lambda constraint for a range. This formulation of specifying
a lambda constraint has the benefit of not needing to hardcode the name
for the coordinate, so that this can be determined at runtime.
The created function uses float values. As a result, a small tolerance is
used to spread the ends of the ranges to help with float equality
matching. Note that the relative tolerance will not affect values of zero.
Adding/subtracting an absolute tolerance is not done due to the
difficulty of selecting an appropriate value given the very small values
of precipitation rates expressed in m s-1.
Args:
coord_name (str):
Name of the coordinate.
values (list):
A list of two values that represent the inclusive end points
of a range.
tolerance (float):
A relative tolerance value to ensure equivalence matching when
using float32 values. Values of zero will be unchanged.
Returns:
iris.Constraint:
Constraint representative of a range of values.
"""
values = [float(i) for i in values]
values = sorted(values)
values[0] = (1. - tolerance) * values[0]
values[1] = (1. + tolerance) * values[1]
constr = (
iris.Constraint(
coord_values={
coord_name: lambda cell: values[0] <= cell <= values[1]}))
return constr