Post by Bryan Post by Miki Tebeka
If you have an interesting/common "Gotcha" (warts/dark corners ...) please share.
Python 3(K) likes to use the same '.py' file extension as its
And so it should.
Python 2 and Python 3 are two dialects of the same language, with just a
very few minor changes in syntax (although a fair number of changes in
libraries). With a modicum of care, it is quite possible, even trivially
easy, to write useful code that is compatible with both Python 2 and 3.
Here's an example:
Post by Bryan
and in some/many/most *nix implementations,
it likes to install in the same place.
I won't speak for Unixes, but that is certainly not the case with Linux.
Each Python version gets its own location:
[steve at ando ~]$ for vers in 2.4 2.5 2.6 3.2 ; do which python$vers ; done
The first, 2.4, is the system python; the others were installed by me. I
didn't need to take any special effort to install to versioned locations,
the make script does that by default. The only special effort needed was
to run "make altinstall" instead of "make install" to ensure that
"python" without a version number still points to the system python
rather than the freshly installed version.
Post by Bryan
Python 3 is an improvement upon
Python 2, but Python went from, "sure... Python just works," to,
"well... that depends... which Python?"
I think that's nonsense. There has never been a time that you didn't have
to think about "which Python", except maybe the very first public
release. Every version has had differences from previous versions -- they
wouldn't be different versions otherwise. Bugs are fixed, but more
importantly new features are added. Libraries are deprecated and then
removed. If you write code using Python 2.4 features, it may not work
with Python 2.3. If you write code using 2.5 features like ternary if
expressions, it certainly will not work in Python 2.4.
The 2to3 transition isn't the only time that Python has made backwards
incompatible changes. I recently had to upgrade some Python code using
string exceptions from Python 2.3 to 2.6. That was tedious but easy.
However getting the tkinter code to upgrade was exciting and difficult.
Another example: the semantics of hex() and oct() have changed, probably
sometime around 2.4 or 2.5. A third: the introduction of nested scopes
back in 2.1. This changed the behaviour of any code using nested
functions, and was the inspiration for the introduction of __future__. A
fourth: turning None into a keyword in version 2.4.
I don't intent to be rude, but anyone who isn't a complete newbie to
programming but is surprised to the point of "gotcha" by version
compatibilities simply hasn't been paying attention.