Diagnosing a Linux-only unit test failure

Post by smitherfield » Mon, Oct 09, 2017, 7:41 PM UTC

philh wrote: post #14

half-kh-hacker wrote: post #10

Earlier quoted context omitted.

I'm not versed in C#, what should you use otherwise?

It's not a C# thing, it's a floating-point thing. Two numbers which mathematically "should" be equal, might not be due to rounding errors. (In python, 0.15 + 0.15 != 0.1 + 0.2.) So it's risky to compare them with ==, sometimes you'll get the result you expect (and sometimes you can be confident of that) but sometimes you won't. If you can't be sure, you should compare that they're the same within some threshold, but…

Post by cyphar » Tue, Oct 10, 2017, 12:47 AM UTC

vog wrote: post #15

cyphar wrote: post #8

Earlier quoted context omitted.

Python added "f strings" recently (read: in 2015)[1], which look like f"{some_var}" which evaluates "some_var" in the local scope. Sort of like Ruby's "#{...}" (if I'm remembering that syntax correctly). Rust supports named parameters in format strings[2] but that's not quite the same. [1]: https://www.python.org/dev/peps/pep-0498/ [2]: https://doc.rust-lang.org/std/fmt/#named-parameters

Note that you can do this in old version of Python, too, using the "format-locals" idiom: some_var = ... "{some_var}".format(**locals()) Although this does have some limitations regarding variables to strictly being in the local scope, this is a fine idiom if you need to be compatible with older Python versions.

  some_var = ...
  "%(some_var)s" % locals()

  some_var = ...
  "%(some_var)s" % dict(globals(), **locals())

  "%(some_var)s" % {**globals(), **locals()}

Post by philh » Tue, Oct 10, 2017, 11:15 AM UTC

estomagordo wrote: post #24

smitherfield wrote: post #21

Earlier quoted context omitted.

`0.1 + 0.2 != 0.3` is a property of all (base-2) floating-point arithmetic, no matter the precision or programming language.

Well yeah, but this was 0.1 + 0.2 != 0.15 + 0.15, and there's no obvious reason why 0.15 + 0.15 = 0.3 imo.