When comparing 2 numbers as "self.assertAlmostEqual(a, b, delta=1000)" the error message looks like this:

    AssertionError: 27332885 != 27391120 within 1000 delta

Especially when a and b are big numbers or differ a lot, it would be useful to see the absolute difference between the 2 numbers as in:

    AssertionError: 27332885 != 27391120 within 1000 delta (58235 difference)

PR: https://github.com/python/cpython/pull/1331/

Is it worth to output a difference when the delta argument is not passed?

Is it worth to output a signed difference rather than an absolute value?

Thanks for chiming in.

> Is it worth to output a difference when the delta argument is not passed?

Yes, probably. I will change that.

> Is it worth to output a signed difference rather than an absolute value?

Mmmm probably not IMHO. Personally I never care about the position of left and right arguments. I just want to check whether a and b are almost equal.

Done.

The patch looks good to me.

New changeset 5d7a8d0c13737fd531b722ad76c505ef47aac96a by Giampaolo Rodola in branch 'master':
bpo-30190: improved error msg for assertAlmostEqual(delta=...) (#1331)
https://github.com/python/cpython/commit/5d7a8d0c13737fd531b722ad76c505ef47aac96a

New test produce deprecation warnings:

/home/serhiy/py/cpython/Lib/unittest/test/test_assertions.py:228: DeprecationWarning: invalid escape sequence \(
  ["^1 != 2 within 7 places \(1 difference\)$", "^oops$",
/home/serhiy/py/cpython/Lib/unittest/test/test_assertions.py:229: DeprecationWarning: invalid escape sequence \(
  "^1 != 2 within 7 places \(1 difference\)$",
/home/serhiy/py/cpython/Lib/unittest/test/test_assertions.py:230: DeprecationWarning: invalid escape sequence \(
  "^1 != 2 within 7 places \(1 difference\) : oops$"])

Mmm I can't see them. Am I supposed to enable this kind of warning somehow?

$ ./python -Wa Lib/unittest/test/test_assertions.py
Lib/unittest/test/test_assertions.py:228: DeprecationWarning: invalid escape sequence \(
  ["^1 != 2 within 7 places \(1 difference\)$", "^oops$",
Lib/unittest/test/test_assertions.py:229: DeprecationWarning: invalid escape sequence \(
  "^1 != 2 within 7 places \(1 difference\)$",
Lib/unittest/test/test_assertions.py:230: DeprecationWarning: invalid escape sequence \(
  "^1 != 2 within 7 places \(1 difference\) : oops$"])
...................................
----------------------------------------------------------------------
Ran 35 tests in 0.052s

OK

Warnings are not shown when the source is already compiled to .pyc file.

$ find -name '*.py[co]' -exec rm '{}' +
$ ./python -Wa -m test test_unittest
Run tests sequentially
0:00:00 load avg: 0.54 [1/1] test_unittest
/home/serhiy/py/cpython/Lib/unittest/test/test_assertions.py:228: DeprecationWarning: invalid escape sequence \(
  ["^1 != 2 within 7 places \(1 difference\)$", "^oops$",
/home/serhiy/py/cpython/Lib/unittest/test/test_assertions.py:229: DeprecationWarning: invalid escape sequence \(
  "^1 != 2 within 7 places \(1 difference\)$",
/home/serhiy/py/cpython/Lib/unittest/test/test_assertions.py:230: DeprecationWarning: invalid escape sequence \(
  "^1 != 2 within 7 places \(1 difference\) : oops$"])
1 test OK.

Total duration: 5 sec
Tests result: SUCCESS

OK thanks. Fix coming.

Reopening as it needs backports for 2.7, 3.3, 3.4, 3.5 and 3.6.

Sorry, I accidentally picked up the wrong thread.