Changes between Version 74 and Version 75 of DeveloperGuidelines/Py_2_3

Timestamp:

07/10/19 22:31:41 (6 years ago)

Author:

Dominic König

Comment:

--

DeveloperGuidelines/Py_2_3

@@ -315 +315 @@
 l.sort(key=lambda item: item if item is not None else -float('inf'))
 }}}
+
+=== Turkish letters İ and ı ===
+
+In Turkish, the letters {{{I}}} and {{{i}}} are not a upper/lowercase pair. Instead, there are two pairs {{{(İ, i)}}} and {{{(I, ı)}}}, i.e. one with and one without the dot above.
+
+According to the Unicode spec, the lowercase pendant for {{{İ}}} is a sequence of two unicode characters, namely the {{{i}}} (with the dot) and the code point U0307 which mean "with dot above". The latter is there to preserve the information about the dot for the conversion back to uppercase.
+
+Python-2 did not implement the U0307 character, so it converted the letters like this:
+{{{#!python
+>>> u"İ".lower().upper()
+u'I'
+>>> u"ı".upper().lower()
+u'i'
+
+# NB with utf-8-encoded str, Python-2 doesn't "İ".lower() at all!
+>>> print "İ".lower()
+İ
+}}}
+
+Python-3 does implement the U0307 character, so the behavior is different:
+{{{#!python
+>>> "İ".lower().upper()
+'İ'
+>>> "ı".upper().lower()
+'i'
+}}}
+
+Critically, the U0307 character changes the string length (it's an extra character!):
+{{{#!python
+# Python-2
+>>> len(u"İ".lower())
+1
+
+# Python-3
+>>> len("İ".lower())
+2
+}}}
+
+This is just something to keep in mind - an actual forward/backward compatibility pattern must be developed for the specific use-case. Neither the Python-2 nor the Python-3 are particularly helpful for generalization, the Turkish I's always need special treatment.