How to Solve the UnicodeDecodeError: 'ascii' codec can't decode byte in Python 2.x?

UnicodeDecodeError: 'ascii' Codec Can't Decode Byte

Facing the UnicodeDecodeError: 'ascii' codec can't decode byte in Python 2.x indicates an attempt to convert a Python 2.x str containing non-ASCII characters to a Unicode string without specifying the encoding of the original string.

Unicode Zen in Python 2.x

Unicode strings, distinct from strings, hold Unicode point codes and can represent any Unicode point across the spectrum. Strings, on the other hand, contain encoded text like UTF-8, UTF-16, or ISO-8895-1. Strings are decoded into Unicode and vice versa. Files and text data are always transferred in encoded strings.

The Markdown module employs unicode() to validate incoming strings, ensuring they are either ASCII or re-wrapped Unicode strings. Since the Markdown authors can't determine the encoding of the incoming string, they rely on users to decode strings into Unicode before passing them on.

Unicode strings can be declared in code using the 'u' prefix before the string. For instance:

my_u = u'my ünicôdé strįng'

Gotchas

Even without an explicit unicode() call, conversions from str to Unicode can occur. The following situations can trigger UnicodeDecodeError exceptions:

• Explicit conversion without encoding: unicode('€')
• Using new style format strings with Unicode strings: u"The currency is: {}".format('€')
• Using old style format strings with Unicode strings: u'The currency is: %s' % '€'
• Appending strings to Unicode: u'The currency is: ' '€'

Input and Decoding

Source Code: Non-ASCII characters can be included in the source code using Unicode strings with the 'u' prefix. To enable Python to decode source code properly, a correct encoding header must be included. For UTF-8 files, use:

# encoding: utf-8

Files: Use io.open with the correct encoding to decode files on the fly. For example, for a UTF-8 file:

import io
with io.open("my_utf8_file.txt", "r", encoding="utf-8") as my_file:
  my_unicode_string = my_file.read()

Databases: Configure databases to return Unicode strings and use Unicode strings for SQL queries.

HTTP: Web pages can have varying encodings. Python-Requests returns Unicode in response.text.

Manually: Decode strings manually using my_string.decode(encoding), where encoding is the appropriate encoding.

Python 3

Python 3 handles Unicode slightly differently than Python 2.x. The regular str is now a Unicode string, and the old str is now bytes.

In Python 3, the default encoding is UTF-8, so decoding a byte string without specifying an encoding uses UTF-8. Additionally, open() operates in text mode by default, returning decoded str (Unicode strings).

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