Python 2.7 io.open: Use "from io import open" or "io.open()"? [duplicate]

Question

I’m working on some code that should run under both Python 2.7.x and Python 3.3+ unchanged, and uses Unicode data text file I/O.

So which is better—and why?

Variant 1:

import io
encoding = 'utf-8'

with io.open('Unicode.txt', 'w', encoding=encoding) as f:
    …
with io.open('Unicode.txt', 'r', encoding=encoding) as f:
    …

Variant 2:

from io import open
encoding = 'utf-8'

with open('Unicode.txt', 'w', encoding=encoding) as f:
    …
with open('Unicode.txt', 'r', encoding=encoding) as f:
    …

Personally, I’d tend to use Variant 2, because the code should be as Python-3-ish as possible, just providing backport stubs for Python 2.7.x. It also looks cleaner and I wouldn’t have to change existing code much. Also I think maybe I could save a little by not importing the whole io module.

You always import a whole module. The only difference this makes is what name is bound in your current module globals (so either io is bound, or open is bound). — Martijn Pieters
– Martijn Pieters, Commented Nov 25, 2016 at 17:23
@MartijnPieters this is not a duplicate of the other question. It's specific to 'open'. Using Variant 2 means that you can just delete the whole import line once Python 3 has been fully adopted. — Emil
– Emil, Commented Dec 5, 2017 at 20:43
Voting to reopen because the duplicate is about general importing style, while this question was really about future-proofing the open() function. — joanis
– joanis, Commented Jul 19, 2022 at 16:35

lmiguelvargasf · Accepted Answer · 2019-06-26 04:07:10Z

0

As @smido has pointed out in a comment, open is a built-in in both Python 2 and 3, then it is already available in both versions of Python without any imports.

Now, assuming that you are asking about what is a better way to import a package, i.e., import module vs from module import ..., formally there is no better way, it is up to you, but I think it is good to use variant 1 since in case you will use another module that has a function called open(), the last import will override the former.

You are right that in general in Python 3 is very common to use from module import field, but I personally would use the first variant. In the end, if you are worried about typing more, a good editor or IDE would help you. :-)

edited Jun 26, 2019 at 4:07

answered Nov 25, 2016 at 17:23

lmiguelvargasf

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4 Comments

smido Over a year ago

open is a built-in in both python 2 and python 3, so you already have the open imported on both pythons. the import from io import open will only change what's used in python2. This is against the argument that 'you shouldn't do this because you might want to use some other open from other module'

lmiguelvargasf Over a year ago

@smido, thanks for the observation. I have updated my answer.

joanis Over a year ago

This answer is missing the whole point of the question. The question was not at all about the best import style. It was specifically about future-proofing the code. And OP's variant 2 in the option that would best future-proof the code.

joanis Over a year ago

The key point of this question is that Python 2's default open() function does not support utf-8, whereas Python 3's does, and so does io.open. Adding the line from io import open makes code look the same in Python 2 and Python 3 from that point on in the file.

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