4 ms·

What I wonder is why one would assume the python command would run python 2, instead of running python 1, assuming python 1 was a thing. By your logic, shouldn

What I wonder is why one would assume the python command would run python 2, instead of running python 1, assuming python 1 was a thing. By your logic, shouldn't python2, run python3 run python 3, etc. What I'm getting at, is we get used to things being a certain way, but often we're just following a convention that was set in place before we got onboard. Why do we still type "bash" instead of "bash4"?

gravypod 10y ago
> Why do we still type "bash" instead of "bash4" Because Bash was made by, and is maintained by, people who understand how backwards compatability in their program is important.
- hobarrera 10y ago
  Just like python. That's why they bumped the major when release backwards-incompatible changes, which is the right thing to do.
CJefferson 10y ago
The reason you would assume it is that, for a long time on every Linux distribution, there was a single way to run python2, and it was called 'python'. I'm not sure what you are getting at, this was just the way it was. You couldn't run python 2 any other way in some linux distros. The reason we don't need a 'bash4' is that, by and large, bash tried very hard to make sure they didn't break any bash3 scripts, so there is no need for old bash3 scripts to know they are now running in bash4, unlike python3.
- michrassena 10y ago
  I get the point, python 2 scripts aren't fully compatible with python 3. I've written a little python and know that to be the case. However, I can predict with near certaintly, if python 4 doesn't break python 3 scripts, people will complain if "python3" doesn't invoke python 4, because they've always used "python3" to run the new python and "python" to run python 2.
- deleted 10y ago
  [deleted]
AsyncAwait 10y ago
Why not be explicit with 'python2' and be done with it?
- Zancarius 10y ago
  I agree, but I'd guess the chief complaint is that doing so requires the `python2` symlink to be available. There's at least one claim up thread that it doesn't exist on all systems (create it yourself?). I didn't catch the distribution used, but I DID check an older Ubuntu image I have (I run Arch) and there's definitely a python2 link pointing to python2.7 (`python` also points to python2.7 and there's a `python3` symlink that does what you'd expect). So outside some LTS build, it seems surprising to me that it wouldn't exist in 2017 on a modern distro. I still can't shake the feeling that the thread started around a relatively insignificant complaint (dumping Arch because they use Python3 by default? Come on...). Personally, I'd rather just use `/usr/bin/env python2` to invoke the appropriate interpreter (if you don't need to pass arguments to it), and if the symlink doesn't exist, the onus is on the user to create it. This is ESPECIALLY true for older distros. Plus, for a sufficiently complicated application, why would someone want to pollute the global site-packages anyway? I'd rather manage most things inside a virtualenv or similar (pick your Python version), because I've seen far too many install_requires/requirements locking to a specific library version.
  - CJefferson 10y ago
    In 2017, indeed everyone has added python2, but I assure you it wasn't that way when Arch originally did the python3 -> python rename. While this is a small issue, this original thread used it as an example of how Arch is good and pragmatic. To me it seemed like the opposite -- it broke lots of code and packages for no good reason. Why should users of older distros have to add a symlink, when before Arch everyone could be sure that '/usr/bin/python' if present would be python2, and '/usr/bin/python3', if present, would be python3? Now I agree that using virtualenv or similar is a good idea, but this actually caused the most problems for little 20 line python scripts, because often the users of those didn't even realise they were using python.
    - 10y ago

gravypod 10y ago

> Why do we still type "bash" instead of "bash4" Because Bash was made by, and is maintained by, people who understand how backwards compatability in their program is important.

hobarrera 10y ago
Just like python. That's why they bumped the major when release backwards-incompatible changes, which is the right thing to do.

CJefferson 10y ago

The reason you would assume it is that, for a long time on every Linux distribution, there was a single way to run python2, and it was called 'python'. I'm not sure what you are getting at, this was just the way it was. You couldn't run python 2 any other way in some linux distros. The reason we don't need a 'bash4' is that, by and large, bash tried very hard to make sure they didn't break any bash3 scripts, so there is no need for old bash3 scripts to know they are now running in bash4, unlike python3.

michrassena 10y ago
I get the point, python 2 scripts aren't fully compatible with python 3. I've written a little python and know that to be the case. However, I can predict with near certaintly, if python 4 doesn't break python 3 scripts, people will complain if "python3" doesn't invoke python 4, because they've always used "python3" to run the new python and "python" to run python 2.
deleted 10y ago
[deleted]

AsyncAwait 10y ago

Why not be explicit with 'python2' and be done with it?

Zancarius 10y ago
I agree, but I'd guess the chief complaint is that doing so requires the `python2` symlink to be available. There's at least one claim up thread that it doesn't exist on all systems (create it yourself?). I didn't catch the distribution used, but I DID check an older Ubuntu image I have (I run Arch) and there's definitely a python2 link pointing to python2.7 (`python` also points to python2.7 and there's a `python3` symlink that does what you'd expect). So outside some LTS build, it seems surprising to me that it wouldn't exist in 2017 on a modern distro. I still can't shake the feeling that the thread started around a relatively insignificant complaint (dumping Arch because they use Python3 by default? Come on...). Personally, I'd rather just use `/usr/bin/env python2` to invoke the appropriate interpreter (if you don't need to pass arguments to it), and if the symlink doesn't exist, the onus is on the user to create it. This is ESPECIALLY true for older distros. Plus, for a sufficiently complicated application, why would someone want to pollute the global site-packages anyway? I'd rather manage most things inside a virtualenv or similar (pick your Python version), because I've seen far too many install_requires/requirements locking to a specific library version.
- CJefferson 10y ago
  In 2017, indeed everyone has added python2, but I assure you it wasn't that way when Arch originally did the python3 -> python rename. While this is a small issue, this original thread used it as an example of how Arch is good and pragmatic. To me it seemed like the opposite -- it broke lots of code and packages for no good reason. Why should users of older distros have to add a symlink, when before Arch everyone could be sure that '/usr/bin/python' if present would be python2, and '/usr/bin/python3', if present, would be python3? Now I agree that using virtualenv or similar is a good idea, but this actually caused the most problems for little 20 line python scripts, because often the users of those didn't even realise they were using python.
  - 10y ago