Question

I have a function:

from django.contrib.gis.measure import Distance, D

def RunLengthCalc(mod_ewdim, mod_ewspacing, cols):
    y = D(inch=mod_ewspacing)  # user input
    x = D(inch=mod_ewdim)  # user input
    z = D(inch=3)  # constant
    lrun = ((x * cols) + (y * (cols - 1))) + zrun
    return lrun

and my test:

def test_run_length_calculation(self):
    l = RunLengthCalc(26.5, 1, 25)
    self.assertEquals(l, D(inch=689.5))

but when I run the test I get this very confusing error:

AssertionError: Distance(inch=689.5) != Distance(inch=689.5)

I can’t work out what the problem is here.

Any help would be much appreciated.

Answer 1

There seems to be some funny business with how the Distance class equality is actually implemented:

https://github.com/django/django/blob/master/django/contrib/gis/measure.py#L87

Reading that code, it looks like what you have should work… but apparently it doesn’t.

I suspect you can fix your problem by comparing specific unit values like so:


self.assertEquals(l.inch, D(inch=689.5).inch)