Backporting Python 3 Open to Python 2

General Discussions
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1

How can I backport Python 3’s open(encoding="utf-8") to Python 2?

I have a Python codebase built for Python 3, which uses the open() function with the encoding parameter:

with open(fname, "rt", encoding="utf-8") as f:

Now, I want to backport this code to Python 2.x, so that it works with both Python 2 and Python 3. What’s the recommended strategy to handle the differences in the open() function and the lack of the encoding parameter in Python 2?

Is there a way to use a Python 3-style open() that works with bytestrings, so it behaves like Python 2’s open()?

2

Oh, I’ve handled this before, and I can tell you what works best.

Use io.open() for Compatibility In Python 2, the open() function does not support the encoding parameter. However, you can use the io module to bridge the gap. The io.open() function behaves like Python 3’s open() and supports the encoding argument.

Here’s how you can do it:

import io

with io.open(fname, "rt", encoding="utf-8") as f:
    # Your code here

This works seamlessly in both Python 2 and Python 3 because io.open() correctly handles the encoding parameter in both versions. If you ask me, it’s the simplest and most portable approach.

3

I’ve done something similar in one of my projects and have an alternative perspective.

Handle Python 2 and 3 Separately with Compatibility Libraries If you’re looking for flexibility and want your codebase to adapt across Python versions without worrying about io, libraries like six or future can simplify this process. They provide utilities for version-agnostic compatibility.

Here’s an example using six:

import six

with six.open(fname, "rt", encoding="utf-8") as f:
    # Your code here

The six.open() function acts as a wrapper, adding support for the encoding argument and behaving consistently across Python 2 and 3. Using a library like six keeps your code cleaner and more maintainable in mixed environments.

If you already use six for other cross-version compatibility, this approach integrates beautifully into your workflow.

4

Adding to the great suggestions above, here’s another option for those times when external libraries or io.open() aren’t feasible.

Manual Encoding Handling for Python 2 If you cannot rely on io.open() or compatibility libraries, you can manage encoding yourself. While slightly less elegant, this approach is straightforward and works reliably.

import sys

if sys.version_info[0] < 3:
    # Python 2.x
    with open(fname, "rb") as f:
        content = f.read().decode("utf-8")
else:
    # Python 3.x
    with open(fname, "rt", encoding="utf-8") as f:
        content = f.read()

# Use the 'content' variable for further processing

In this method, you open the file in binary mode (rb) in Python 2, then manually decode the content to utf-8. For Python 3, you use the native open() with the encoding parameter. While this introduces a bit more boilerplate, it ensures that your python open encoding logic is explicit and adaptable.