Lesson One - Messing Around Until Something Useful Happens

The first step to enriching your life with a fine programming language like Python is having it available. If you are using Linux or a recent Mac OS, then it's already there. If you are not, you should work on that problem. (If you're really in a bind, this is a nice workaround: http://www.cygwin.com/.)

At this point I'll assume that you have access to Python. How would you know for sure? Type something like this at a terminal's command prompt:

$ python -V

If you're lucky, this spits out something like:

Python 2.4.2

"Programming in Python" sounds so intense, so let's start by "messing around with Python" which is gratifying in a much more instantaneous way. Simply type:

$ python

And you get some mess like this:

Python 2.4.2 (#1, Oct 27 2005, 10:21:56) [GCC 3.3.6 (Gentoo 3.3.6, ssp-3.3.6-1.0, pie-8.7.8)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>>

Now you are not in your normal shell's interactive mode - you are in the Python shell. It turns out that you could use this Python shell instead of your normal shell (bash or tcsh), but that would be weird and you'd better wait until you're really gung-ho about Python for that.

The reason the Python shell is so great is that one can test little bits of code to see how they work. This is a fantasticly helpful ability when programming, debugging, and especially when learning Python. This is why we're starting with it.

Since you may not know any Python now, you'll have nothing to test. That's ok. The Python shell (or Python Interactive Interpreter) is extremely handy in day to day life without much knowledge of Python at all. I find that it makes a terrific desktop calculator.

Let's say you want to know how much time per year you waste driving to work measured in days. Say 50 work weeks a year, 5 days per week, .6 hour each way. Just type this:

>>> 50 * 5 * .6 * 2 300.0

That's pretty easy. Now here comes a little problem. Let's say you wanted to put that in context of how many equivalent 8 hour workdays are lost. One might assume that this would work:

>>> 300 / 8 37

The problem is, this answer is kind of wrong. Python does a great job as a personal calculator, but you must be very careful about this fact: Python prefers integer division. This means that if you give Python 2 whole integers (no decimal), it will give you an answer that is also a whole integer, and that will be inaccurate most of the time. Fortunately, the answer to the problem is simple:

>>> 300 / 8.0 37.5

There you go. In this hypothetical situation, a person who traded a .6 hour commute for a productive bus/limo ride would get the equivalent of 37.5 days at work to do whatever they wanted!

Python has other tricks that are helpful when using it as a calculator. One of Python's strengths is a large and well-organized collection of "modules" which can be imported into a Python environment at any time on an as needed basis. Here is an example:

>>> import math

Nothing much seems to happen, but now you can do stuff like this:

>>> math.sin( math.pi / 2 ) 1.0

Note that here you don't need to say 2.0 because pi is a decimal number, and therefore so is the result. There are lots of things the math module can do, but the most intersting thing to explore now is this Python trick:

>>> help('math')

Don't worry if you don't think you'll ever need this kind of fancy math. The point here is the built-in help facility that can often help you out when you don't know what your options are or how to use them.

Play around with the Python interpreter and see if you can convince yourself that it would sometimes make a nice calculator.