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Comment by rdtsc | Hacker News Reader

> and even most Linux distros are at least at Python 3.2

Why are you spreading lies? You are hurting your cause (advocating Python 3).

Let's take a look at latest Ubuntu:

   $ cat /etc/issue
   Ubuntu 14.04 LTS \n \l

   $ python --version
   Python 2.7.6

How about the popular server distro CentOS 6?

  $ cat /etc/issue
   CentOS release 6.5 (Final)
   Kernel \r on an \m

   $ python --version
   Python 2.6.6

What exactly are these "most" Linux distros everyone is using that I haven't heard of?

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> Why are you spreading lies?

Why are you assuming the worst possible intent on my part, instead of asking what I meant?

I meant the distros have Python 3 available, not that they make it the default that /usr/bin/python points to. Ubuntu has had Python 3 available for quite a number of releases; I run 12.04 which has Python 3.2 (and I've had it installed since I installed Ubuntu). According to the release notes[1], Ubuntu 14.04 makes Python 3.4 available, and work is ongoing to make it the default Python for Ubuntu. They also advise porting to Python 3.

It looks like CentOS makes Python 3.2 available, but I can't be sure from their online documentation.

[1] https://wiki.ubuntu.com/TrustyTahr/ReleaseNotes

> most Linux distros are at least at Python 3.2.

I don't know how else to interpret that besides "the base version of python in those latest distros is at least 3.2"

Shipping it as an "alternative" just splits the library world into to. So that is not a distro being "at" a python version.

> It looks like CentOS makes Python 3.2 available,

It does. Do all the python-* libraries work with it. Or do I have to install those separately?

> I don't know how else to interpret that besides "the base version of python in those latest distros is at least 3.2"

Then you could have said that, or asked if there was another way to interpret it, instead of starting with "why are you spreading lies".

> It does. Do all the python- libraries work with it. Or do I have to install those separately?*

If CentOS works like Ubuntu, then there will be python3-* libraries for use with Python 3.

> "why are you spreading lies".

But I also didn't say you are spreading lies maliciously. You can spread them unknowingly via mis-communication.

I could post something like "Large parts of the Linux kernel are written in C++". And it would be spreading lies. But it could be just be me being confused as well or thinking that a C++ compiler will compile C and that C is a largely a subset of C++.

> I also didn't say you are spreading lies maliciously

My objection wasn't that you imputed malice; it was that you went straight to "spreading lies" instead of expressing uncertainty about what I meant. And you were wrong about what I meant.

> You can spread them unknowingly via mis-communication.

Which, since you were wrong about what I meant, is what you did when you said I was "spreading lies".

Many distros include both Python 2 and Python 3 support. I think pdonis is saying that distros that support Python 3 are not stuck on 3.0. That is, their Python 3 packages are 3.2 or higher, so comparing 2.7 to 3.0 is unreasonable, since it's not a choice anyone has to make. Which seems to be true. For example, the relatively conservative Debian is currently on Python 3.2, with Python 3.3 in the next version. Ubuntu's python3 is currently 3.4. Fedora appears to be 3.2. Arch has Python 3.4, I think.

So what pdonis was saying is, as far as I can tell, true.

They do. But python3 is not the default python.

Download a python script run it and it will run on Python 2.7.6.

Yes that OP meant to say that because he clarified it later. But I don't see how his original comment of:

> most Linux distros are at least at Python 3.2

implies that. To me that says 3.2+ ships as the default version of Python.

> python3 is not the default python.

The post I was responding to talked about books on Python for students, presumably students studying programming. Python 3 doesn't need to be the default python for students studying programming to use it; it just needs to be available. If the post had been talking about, say, sysadmins, that would be a different story.

I think it's recommended for distros to modify the shebang to /usr/bin/env python3 for script that are supposed to run under python 3, although this does pose a problem for scripts that want to run under both without modification. If the distro ships with python3 and most of the system scripts run under python3 I'd say its the default.Ubuntu for one is planning on not shipping a python2 or /usr/bin/python binary by default(although it will still be in repos) eventually.

I think 3.0 was meant to be 3.x not 3.0 specifically.

You should try to run

    $ python3 --version

...instead.

Will the programs or scripts I download know to to that?

Any script worth it's salt that depends on a newer feature of Python 3 can just check `sys.version_info`. This was a thing one had to consider back when new versions of Python 2.x were coming out, too.

It's not quite that simple. Not all code that runs on Python 2 will be syntax-compatible with Python 3, and vice versa. You can, with some effort, use a subset of the Python syntax that is compatible with both interpreters, but many libraries do not do that, but ship separate Python 2 and Python 3 versions if they support both.

Syntax changes can be an issue for backwards compatibility, but that's not what I was talking about.

It's easy to specify what the minimum version of Python you want to support is. Even if there's syntax which is incompatible with Python 2 in the file, a hashbang that specifies `python3` is pretty clear.

Yes, #!/usr/bin/python3 is clear, but I don't think it addresses the question you were responding to, which was whether the scripts the OP of this subthread was talking about, which he knows will run under Python 2 (because he downloaded them and ran them under Python 2--he mentioned this in another subthread), will know to check for the presence of Python 3 and use it. Any such script will have to check sys.version_info to know which version of Python it is running under (and for at least one version the shebang will be irrelevant anyway since it can only specify python or python3, not both), and it will have to be syntax-compatible with both versions. If the script isn't syntax-compatible with Python 3, then he'll have to go find and download a version that is, if it exists.

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