Sometimes, white space (spaces, tabs, newlines, and their ilk) is more trouble than it's worth. Maybe you want to be able to break a single line of expected output across several lines in your test file, or maybe you're testing a system that uses lots of white space but doesn't convey any useful information with it.
The doctest gives you a way to "normalize" white space, turning any sequence of white space characters, in both the expected output and in the actual output, into a single space. It then checks whether these normalized versions match.
We're going to write a couple of tests that demonstrate how whitespace normalization works.
Insert the following code into your doctest file:
Next, a demonstration of whitespace normalization.
>>> [1, 2, 3, 4, 5, 6, 7, 8, 9]
... # doctest: +NORMALIZE_WHITESPACE
[1, 2, 3,
4, 5, 6,
7, 8, 9]
>>> sys.stdout.write("This text
contains weird spacing.
")
... # doctest: +NORMALIZE_WHITESPACE
This text contains weird spacing.
39Both of these tests pass, in spite of the fact that the result of the first one has been wrapped across multiple lines to make it easy for humans to read, and the result of the second one has had its strange newlines and indentations left out, also for human convenience.
Notice how one of the tests inserts extra whitespace in the expected output, while the other one ignores extra whitespace in the actual output? When you use +NORMALIZE_WHITESPACE, you gain a lot of flexibility with regard to how things are formatted in the text file.
Note
You may have noted the value 39 on the last line of the last example. Why is that there? It's because the write() method returns the number of bytes that were written, which in this case happens to be 39. If you're trying this example in an environment that maps ASCII characters to more than one byte, you will see a different number here; this will cause the test to fail until you change the expected number of bytes.