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| -rw-r--r-- | Doc/library/doctest.rst | 18 |
1 files changed, 11 insertions, 7 deletions
diff --git a/Doc/library/doctest.rst b/Doc/library/doctest.rst index 587a0a0..bc5a404 100644 --- a/Doc/library/doctest.rst +++ b/Doc/library/doctest.rst @@ -759,23 +759,27 @@ Warnings :mod:`doctest` is serious about requiring exact matches in expected output. If even a single character doesn't match, the test fails. This will probably surprise you a few times, as you learn exactly what Python does and doesn't -guarantee about output. For example, when printing a dict, Python doesn't -guarantee that the key-value pairs will be printed in any particular order, so a -test like :: +guarantee about output. For example, when printing a set, Python doesn't +guarantee that the element is printed in any particular order, so a test like :: >>> foo() - {"Hermione": "hippogryph", "Harry": "broomstick"} + {"Hermione", "Harry"} is vulnerable! One workaround is to do :: - >>> foo() == {"Hermione": "hippogryph", "Harry": "broomstick"} + >>> foo() == {"Hermione", "Harry"} True instead. Another is to do :: - >>> d = sorted(foo().items()) + >>> d = sorted(foo()) >>> d - [('Harry', 'broomstick'), ('Hermione', 'hippogryph')] + ['Harry', 'Hermione'] + +.. note:: + + Before Python 3.6, when printing a dict, Python did not guarantee that + the key-value pairs was printed in any particular order. There are others, but you get the idea. |