Why Does Decoding a String with \'utf-8\' Result in a \'UnicodeDecodeError: invalid continuation byte\' While \'latin-1\' Succeeds?

Unicode Encoding Error: Invalid Continuation Byte

Question:

Decoding a string using the 'utf-8' codec results in a 'UnicodeDecodeError: invalid continuation byte' exception, but succeeds with the 'latin-1' codec. Why is this happening?

Code:

o = "a test of \xe9 char"
v = o.decode("utf-8")

Solution:

UTF-8 vs. Latin-1 Encoding

The UTF-8 encoding uses multiple bytes to represent characters, while Latin-1 is a single-byte encoding. In Latin-1, the byte 0xe9 represents the character é.

Invalid Continuation Byte

In UTF-8, the byte 0xe9 is a continuation byte used to indicate that the previous byte is part of a multi-byte character. However, in our string, the byte 0xe9 appears as an isolated byte, which is not allowed in UTF-8.

Using Latin-1

Because Latin-1 interprets 0xe9 as a character rather than a continuation byte, the decoding succeeds with the 'latin-1' codec. However, this approach is not ideal, as it may lead to errors if the expected encoding is actually UTF-8.

Additional Context

This error can occur when reading data from sources that do not explicitly specify the encoding or when working with legacy systems that use Latin-1-encoded data.

Resolution:

To resolve the issue, ensure that the correct encoding is being used for decoding and encoding data. For files with known or expected UTF-8 encoding, use UTF-8 when opening files and decoding text. For data received from untrusted sources or systems with unknown encoding, consider using universal codecs such as 'utf-8-sig' or 'chardet' to automatically detect the correct encoding.

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