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There are pieces of Python 3 that are syntax errors in Python 2. And there are Python 2-isms that are valid syntax in Python 3 but have a different interpretati

by aston 13y ago

There are pieces of Python 3 that are syntax errors in Python 2. And there are Python 2-isms that are valid syntax in Python 3 but have a different interpretation. It's not as simple as importing certain features (which creates a sort of language version hybrid). The idea to allow one project to switch between Python 2 and Python 3 for individual files is more interesting, but practically speaking would lead to sort of a mess.

pak 13y ago
>The idea to allow one project to switch between Python 2 and 3 for individual files Yes, I believe key parts of the standard object model changed between the two (e.g. strings vs bytes, many of the magic methods and operators) making this nearly impossible. Every time objects would pass back and forth, they'd have to be converted, which is wasteful and bug-prone (and this is a whole mess of library code that the python3 guys probably did not want to write). You'd also need to load two different standard libraries, which would waste memory. You only need to scan through the upgrade feature list to see how hard intercompatibility would have been. http://docs.python.org/3.0/whatsnew/3.0.html http://docs.python.org/3.0/whatsnew/3.0.html Although I totally agree with Aaron that this would have allowed people to actually use Python 3 without fear, anything short of forcing the entire program and all of its modules to run in v3 mode as opposed to v2 mode would have been a disaster from a reliability and technical design standpoint. And that's closer to how things actually went down with 2to3, etc.
- jfaucett 13y ago
  thanks for that link, now I see the problems Text Data vs. Unicode alone would be an enormous overhaul. Though the syntax changes dont seem that problematic.
  - bskap 13y ago
    They aren't. And there are automatic tools for converting between them (2to3 and 3to2), along with those __future__ imports that Aaron mentioned: doing "from __future__ import print_function, unicode_literals, absolute_import, division" would give you most of the Python 3 syntax changes in Python 2. The "everything expects bytes" to "everything expects text" change is the biggest hurdle for a lot of projects.

by aston 13y ago

pak 13y ago

>The idea to allow one project to switch between Python 2 and 3 for individual files Yes, I believe key parts of the standard object model changed between the two (e.g. strings vs bytes, many of the magic methods and operators) making this nearly impossible. Every time objects would pass back and forth, they'd have to be converted, which is wasteful and bug-prone (and this is a whole mess of library code that the python3 guys probably did not want to write). You'd also need to load two different standard libraries, which would waste memory. You only need to scan through the upgrade feature list to see how hard intercompatibility would have been. http://docs.python.org/3.0/whatsnew/3.0.html http://docs.python.org/3.0/whatsnew/3.0.html Although I totally agree with Aaron that this would have allowed people to actually use Python 3 without fear, anything short of forcing the entire program and all of its modules to run in v3 mode as opposed to v2 mode would have been a disaster from a reliability and technical design standpoint. And that's closer to how things actually went down with 2to3, etc.

jfaucett 13y ago
thanks for that link, now I see the problems Text Data vs. Unicode alone would be an enormous overhaul. Though the syntax changes dont seem that problematic.
- bskap 13y ago
  They aren't. And there are automatic tools for converting between them (2to3 and 3to2), along with those __future__ imports that Aaron mentioned: doing "from __future__ import print_function, unicode_literals, absolute_import, division" would give you most of the Python 3 syntax changes in Python 2. The "everything expects bytes" to "everything expects text" change is the biggest hurdle for a lot of projects.