Python UnicodeDecodeError - Am I misunderstanding encode?

Question

Any thoughts on why this isn't working? I really thought 'ignore' would do the right thing.

>>> 'add \x93Monitoring\x93 to list '.encode('latin-1','ignore')
Traceback (most recent call last):
  File "<interactive input>", line 1, in ?
UnicodeDecodeError: 'ascii' codec can't decode byte 0x93 in position 4: ordinal not in range(128)

Answer 1

encode is available to unicode strings, but the string you have there does not seems unicode (try with u'add \x93Monitoring\x93 to list ')

>>> u'add \x93Monitoring\x93 to list '.encode('latin-1','ignore')
'add \x93Monitoring\x93 to list '

Answer 2

This seems to work:

'add \x93Monitoring\x93 to list '.decode('latin-1').encode('latin-1')

Any issues with that? I wonder when 'ignore', 'replace' and other such encode error handling comes in?

Answer 3

…there's a reason they're called "encodings"…

A little preamble: think of unicode as the norm, or the ideal state. Unicode is just a table of characters. №65 is latin capital A. №937 is greek capital omega. Just that.
In order for a computer to store and-or manipulate Unicode, it has to encode it into bytes. The most straightforward encoding of Unicode is UCS-4; every character occupies 4 bytes, and all ~1000000 characters are available. The 4 bytes contain the number of the character in the Unicode tables as a 4-byte integer. Another very useful encoding is UTF-8, which can encode any Unicode character with one to four bytes. But there also are some limited encodings, like "latin1", which include a very limited range of characters, mostly used by Western countries. Such encodings use only one byte per character.

Basically, Unicode can be encoded with many encodings, and encoded strings can be decoded to Unicode. The thing is, Unicode came quite late, so all of us that grew up using an 8-bit character set learned too late that all this time we worked with encoded strings. The encoding could be ISO8859-1, or windows CP437, or CP850, or, or, or, depending on our system default.

So when, in your source code, you enter the string "add “Monitoring“ to list" (and I think you wanted the string "add “Monitoring” to list", note the second quote), you actually are using a string already encoded according to your system's default codepage (by the byte \x93 I assume you use Windows codepage 1252, “Western”). If you want to get Unicode from that, you need to decode the string from the "cp1252" encoding.

So, what you meant to do, was:

"add \x93Monitoring\x94 to list".decode("cp1252", "ignore")

It's unfortunate that Python 2.x includes an .encode method for strings too; this is a convenience function for "special" encodings, like the "zip" or "rot13" or "base64" ones, which have nothing to do with Unicode.

Anyway, all you have to remember for your to-and-fro Unicode conversions is:

• a Unicode string gets encoded to a Python 2.x string (actually, a sequence of bytes)
• a Python 2.x string gets decoded to a Unicode string

In both cases, you need to specify the encoding that will be used.

I'm not very clear, I'm sleepy, but I sure hope I help.

PS A humorous side note: Mayans didn't have Unicode; ancient Romans, ancient Greeks, ancient Egyptians didn't too. They all had their own "encodings", and had little to no respect for other cultures. All these civilizations crumbled to dust. Think about it people! Make your apps Unicode-aware, for the good of mankind. :)

PS2 Please don't spoil the previous message by saying "But the Chinese…". If you feel inclined or obligated to do so, though, delay it by thinking that the Unicode BMP is populated mostly by chinese ideograms, ergo Chinese is the basis of Unicode. I can go on inventing outrageous lies, as long as people develop Unicode-aware applications. Cheers!

Answer 4

I also wrote a long blog about this subject:

The Hassle of Unicode and Getting on With It