Python Roadmap Amplifications and Clarifications

Some additional points on using Python 2.7 in a way that bridges the gap to Python 3.2. The steps are small and simple. You can start taking them now.

Recently I suggested that one should always include from __future__ import division, print_function on every module. Always. Every Module.

I also suggested using input=raw_input in those few scripts where input might be expected. This  isn't the best idea, but it forces you to depend on the semantics of the Python 3 input() function.

I failed to mention that you must stop using the % operator for string formatting. This operator will be removed from Python 3.2. Start using "".format() string formatting right now. Always. Every Module.

A follow-up question was "What the heck is from __future__?"

The Python __future__ package contains proposed language changes.

There are a number of modules. Of those, two are highly relevant to easing the switch to 3.2.

Division.

The division module changes the semantics of division. The "/" operator becomes "exact" division instead of "depends on the arguments" division.

In Python2.7, do

>>> 22/7
>>> 22/7.0

To see the "depends on the arguments" (or classical) mode.

Then try

>>> from __future__ import division
>>> 22/7

This is the exact division operation that's used in Python 3.

For integer division, the "//" operator is used.

>>> 22//7

Start now. Use them like this.

Print Function.

The print_function module actually changes the Python compiler to reject the print statement as a syntax error. This allows you to use the (less quirky) print() function.

In Python 3, the print statement has been removed.  It's easiest to simply get out of the habit of using the print statement by switching to the print() function as soon as possible.

This means that examples from older books will have to be translated.

print "hello world"  

becomes

print("hello world")

Not too significant a change, really.

In some later chapters, they may introduce print >> somefile, data, data.

The "chevron print". This syntax was a HUGE blunder, and is one of the reasons for eliminating the print statement and replacing it with the print() function. The print function equivalent is print( data, data, file=somefile ). Much more regular; much less quirky.