How Can I Solve Python's `UnicodeDecodeError: 'ascii' codec can't decode byte...`?

UnicodeDecodeError Resolution: 'ascii' Codec Unable to Decode Byte

Quick Solution

• Avoid unnecessary decoding/encoding.
• Ensure your strings are not assumed as UTF-8 encoded.
• Convert strings to Unicode as early as possible.
• Address locale issues (as described in the linked question).
• Resist the temptation of using quick reload fixes.

Understanding Unicode and Python 2.x

UnicodeDecodeError typically occurs when attempting to convert a Python 2.x string containing non-ASCII characters to Unicode without specifying its encoding.

Unicode strings (type: unicode) represent a sequence of Unicode point codes, while strings (type: str) contain encoded text (e.g., UTF-8, UTF-16). Strings are decoded to Unicode, while Unicodes are encoded to strings.

Numerous scenarios, including explicit conversions, format strings, and string concatenation, can trigger UnicodeDecodeError when handling non-ASCII data.

Input and Decoding

• Use Unicode strings (prefixed with 'u') for non-ASCII characters in source code.
• Provide an encoding header to the source code file to facilitate correct decoding.
• Utilize io.open with appropriate encoding to decode files on the fly.
• Employ backports.csv for non-ASCII CSV files.
• Configure databases to return data in Unicode and use Unicode strings for queries.
• Decode manually using string.decode(encoding) with the correct encoding.

Intermediate Handling

• Operate with Unicode strings as you would with regular strings.

Output

• print encodes Unicodes based on the console's encoding.
• Use io.open to convert Unicodes to encoded byte strings for files.
• Ensure correct database configuration for writing Unicode data.

Python 3 Considerations

While Python 3 handles Unicode better, it's important to understand that it does not come with native Unicode capability. The default encoding is UTF-8, and open() operates in text mode, returning decoded str (Unicode) using the locale encoding.

Avoiding sys.setdefaultencoding('utf8')

This hack masks underlying issues and disrupts the migration to Python 3. Instead, address the root cause and embrace Unicode zen.

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