String completion as you move to Python 3 (OR, how curly braces became important)
I am currently in the midst of (FINALLY!!) making the shift from trusted Python 2.7 to Python 3.x (while recovering from an extended holiday thanks to a somewhat lengthy visa renewal process). Making the shift itself is pretty simple, thanks to a nifty, command line tool built within the Python standard library itself (at least on Linux) called, very simply, 2to3.
Its always a good idea to keep backups of legacy code (of course!), and to actually write changes to file, so the command goes something like:
2to3 -w *.py
I am in the habit of using % as a placeholder for string completion in Python 2.x. That behavior doesn't go out of use entirely in Python 3.x, but using the str.format() method is recommended instead - see more details.
Most of string completion code worked out of the box in Python 3 - I only realized that the norm had changed when I had curly braces "{}" in my strings. It turns out that curly braces have a special meaning in Python 3 strings - they are placeholders, in addition to the % sign. The format goes something like this:
However, the braces themselves need to be encapsulated in a second set of braces to be printed. So, for example:
In brief, the braces outside the number placeholder {:d} have to be encapsulated in a second (or third, depending on how you look at it) set of braces :)