Not x.islower() Versus x.isupper Output Results

[Christopher Reimer]

Greetings,

I was playing around with a piece of code to remove lowercase letters
and leave behind uppercase letters from a string when I got unexpected
results.

string = 'Whiskey Tango Foxtrot'

list(filter((lambda x: not x.islower()), string))

['W', ' ', 'T', ' ', 'F']

Note the space characters in the list.

list(filter((lambda x: x.isupper()), string))

['W', 'T', 'F']

Note that there are no space characters in the list.

Shouldn't the results between 'not x.islower()' and 'x.isupper()' be
identical?

The final form of this code is this:

list(filter(str.isupper, string))

['W', 'T', 'F']

Thank you,

Chris R.

[Steven D'Aprano]

On Sat, 30 Apr 2016 11:14 am, Christopher Reimer wrote:

> Shouldn't the results between 'not x.islower()' and 'x.isupper()' be
> identical?

Of course not.

py> "2 #".islower(), "2 #".isupper()
(False, False)

py> not "2 #".islower(), "2 #".isupper()
(True, False)

"Is Lower" versus "Is Upper" is not a dichotomy. There are:

- lowercase characters, like "abc"
- uppercase characters, like "ABC"
- characters which are neither lowercase nor uppercase, like "2 #"

In unicode, there are also:

- titlecase characters, like "DžLjῼ"

If those characters don't show up for you, they are:

U+01C5 LATIN CAPITAL LETTER D WITH SMALL LETTER Z WITH CARON
U+01C8 LATIN CAPITAL LETTER L WITH SMALL LETTER J
U+1FFC GREEK CAPITAL LETTER OMEGA WITH PROSGEGRAMMENI


So not islower() is very different from isupper.




--
Steven

[Steven D'Aprano]

On Sat, 30 Apr 2016 11:31 am, Steven D'Aprano wrote:

> In unicode, there are also:
>
> - titlecase characters, like "DžLjῼ"

To be clear, each of those three characters is considered titlecased
individually. The three of them together is not considered a title-cased
string.

"Is Title" is not just for Unicode. In Python 2, strings (ASCII byte
strings) also have an istitle() method:

py> "Dz".istitle()
True
py> "DZ".istitle()
False



--
Steven