When is `string.swapcase().swapcase()` not equal to `string`?

Question

Click on this documentation for str.swapcase(), which says:

Return a copy of the string with uppercase characters converted to lowercase and vice versa. Note that it is not necessarily true that s.swapcase().swapcase() == s.

I can't think about an example where s.swapcase().swapcase() != s, would anyone be able to consider one?

Answer 1

Look at this simple example:

s = "ß"

print(s.swapcase().swapcase())

output:

ss

ß is German lowercase double s (The right capitalized form would be ß). The explanation for this happens is that Python doesn't "know" or need to characterize an uppercase conversion for each and every Unicode symbol. So it takes the simple course by assessing s.swapcase() as "SS", so in this manner s.swapcase().swapcase() is "ss".

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