Preserving Encoding When Piping Output in Python

When redirecting the standard output of a Python program through a pipe, the interpreter may incorrectly assume an encoding of None, leading to Unicode encoding errors. To resolve this issue, it's essential to explicitly specify the encoding.

Unlike execution in a script, where Python automatically adjusts to the terminal's encoding, piping requires manual encoding. A common practice is to encode the output using 'utf-8':

# -*- coding: utf-8 -*-
print(u"åäö".encode('utf-8'))

This ensures that the piped output is consistent with the Unicode representation, regardless of the target program's encoding.

For complex scenarios involving multiple encodings, it's recommended to adhere to the following principle:

• Decode input using the expected encoding
• Work with data internally using Unicode
• Encode output using the desired encoding

This approach allows for seamless data manipulation and avoids encoding-related errors.

Consider the example of a Python program that converts between ISO-8859-1 and UTF-8, applying uppercase conversion in the process:

import sys

for line in sys.stdin:
    line = line.decode('iso8859-1')
    line = line.upper()
    line = line.encode('utf-8')
    sys.stdout.write(line)

In this case, the input is decoded from ISO-8859-1, processed as Unicode, and then encoded to UTF-8 before output.

Setting the system's default encoding globally is not advised, as it can interfere with modules and libraries that may assume ASCII encoding.