Decoding bytes to text strings in Python 2
I'm curious about something I've encountered while updating a very old Tk app (originally written in Python 1, but I've ported it to Python 2 as a first step towards getting it running on modern systems). The app downloads emails from a POP server and displays them. At the moment, the code is completely unaware of character encodings (which is something I plan to fix), and I have found that I don't understand what Python is doing when no character encoding is specified. To demonstrate, I have written this short example program that displays a variety of UTF-8 characters to check whether they are decoded properly: Example Code import Tkinter as tk window = tk.Tk() mytext = """ \xc3\xa9 LATIN SMALL LETTER E WITH ACUTE \xc5\x99 LATIN SMALL LETTER R WITH CARON \xc4\xb1 LATIN SMALL LETTER DOTLESS I \xef\xac\x84 LATIN SMALL LIGATURE FFL \xe2\x84\x9a DOUBLE-STRUCK CAPITAL Q \xc2\xbd VULGAR FRACTION ONE HALF \xe2\x82\xac EURO SIGN \xc2\xa5 YEN SIGN \xd0\x96 CYRILLIC CAPITAL LETTER ZHE \xea\xb8\x80 HANGUL SYLLABLE GEUL \xe0\xa4\x93 DEVANAGARI LETTER O \xe5\xad\x97 CJK UNIFIED IDEOGRAPH-5B57 \xe2\x99\xa9 QUARTER NOTE \xf0\x9f\x90\x8d SNAKE \xf0\x9f\x92\x96 SPARKLING HEART """ mytext = mytext.decode(encoding="utf-8") greeting = tk.Label(text=mytext) greeting.pack() window.mainloop() End Example Code This works exactly as expected, with all the characters displaying correctly. However, if I comment out the line 'mytext = mytext.decode (encoding="utf-8")', the program still displays *almost* everything correctly. All of the characters appear correctly apart from the two four-byte emoji characters at the end, which instead display as four characters. For example, the "SNAKE" character actually displays as: U+00F0 LATIN SMALL LETTER ETH U+FF9F HALFWIDTH KATAKANA SEMI-VOICED SOUND MARK U+FF90 HALFWIDTH KATAKANA LETTER MI U+FF8D HALFWIDTH KATAKANA LETTER HE What's Python 2 doing here? sys.getdefaultencoding() returns 'ascii', but it's clearly not attempting to display the bytes as ASCII (or cp1252, or ISO-8859-1). How is it deciding on some sort of almost-but- not-quite UTF-8 decoding? I am using Python 2.7.18 on a Windows 10 system. If there's any other relevant information I should provide please let me know. Many thanks, Rayner -- https://mail.python.org/mailman/listinfo/python-list
Re: Decoding bytes to text strings in Python 2
In article , [email protected] says... > > If you switch to a Linux system, it should work correctly, and you'll > be able to migrate the rest of the way onto Python 3. Once you achieve > that, you'll be able to operate on Windows or Linux equivalently, > since Python 3 solved this problem. At least, I *think* it will; my > current system has a Python 2 installed, but doesn't have tkinter > (because I never bothered to install it), and it's no longer available > from the upstream Debian repos, so I only tested it in the console. > But the decoding certainly worked. Thank you for the idea of trying it on a Linux system. I did so, and my example code generated the error: _tkinter.TclError: character U+1f40d is above the range (U+-U+) allowed by Tcl So it looks like the problem is ultimately due to a limitation of Tcl/Tk. I'm still not sure why it doesn't give an error on Windows and instead either works (when UTF-8 encoding is specified) or converts the out-of-range characters to ones it can display (when the encoding isn't specified). But now I know what the root of the problem is, I can deal with it appropriately (and my curiosity is at least partly satisfied). This has given me a much better understanding of what I need to do in order to migrate to Python 3 and add proper support for non-ASCII characters, so I'm very grateful for your help! Thanks, Rayner -- https://mail.python.org/mailman/listinfo/python-list
Re: Decoding bytes to text strings in Python 2
In article , [email protected] berlin.de says... > > I didn't really do a super thorough deep dive on this, > but I'm just giving the initial impression without > actually being familiar with Tkinter under Python 2, > so I might be wrong! > > The Text widget typically expects text in Tcl encoding, > which is usually UTF-8. > > This is independent of the result returned by sys.get- > defaultencoding()! > > If a UTF-8 string is inserted directly as a bytes object, > its code points will be displayed correctly by the Text > widget as long as they are in the BMP (Basic Multilingual > Plane), as you already found out yourself. Many thanks, you've helped me greatly in understanding what's happening. When I tried running my example code on a different system (Python 2.7.18 on Linux, with Tcl/Tk 8.5), I got the error: _tkinter.TclError: character U+1f40d is above the range (U+-U+) allowed by Tcl So, as your reply suggests, the problem is ultimately a limitation of Tcl/Tk itself. Perhaps I should have spent more time studying the docs for that instead of puzzling over the details of character encodings in Python! I'm not sure why it doesn't give the same error on Windows, but at least now I know where the root of the issue is. I am now much better informed about how to migrate the code I'm working on, so I am very grateful for your help. Thanks, Rayner -- https://mail.python.org/mailman/listinfo/python-list
