[Tutor] A couple newbie questions about Python

[Steven D'Aprano]

Hi Deb,

My responses below, interleaved with your questions.


On Wed, Jun 11, 2014 at 12:46:11PM -0800, Deb Wyatt wrote:

> Hi.  Everywhere I have read, the 'standard practice' for indentation 
> is 4 spaces, but I am running into 2 space indentation in a lot of 
> tutorials and such.  Should I keep with the 4 spaces, or does it even 
> matter, as long as it is consistent?

Four spaces is common, and recommended by "PEP 8", which describes the 
coding styles for the Python standard library:

https://www.python.org/dev/peps/pep-0008

But it's not compulsory (except for contributions to the standard 
library). There are good reasons for sticking to four spaces, but eight 
spaces or a single tab are also common. In my opinion, two spaces is too 
little, and one space is right out.

But as far as the Python interpreter is concerned, it doesn't care, so 
long as you're consistent. (However, other people reading your code may 
care.)


> I just recently became aware of the inaccuracy of calculations using 
> floats and I am concerned about that.

Floating point mathematics is tricky. What you're seeing is not a bug in 
Python, but a general problem with floating point calculations in 
general. Regardless of whether you use Python, or C, or Java, or some 
other programming language, you have to face the same issues that 
calculations with floats are not always accurate compared to what you 
expect from pure mathematics.

(Think about your calculator: how often do you get a number like 
3.0000001 instead of 3, or 0.4999999 instead of 0.5?)

You can read up on some of the issues here:

http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

although it's quite technical. Some less technical discussions can be 
found here:

http://randomascii.wordpress.com/2012/04/05/floating-point-complexities/
http://support.microsoft.com/kb/42980

but however you look at it, it's complicated, and inherent to the 
problem, not the fault of Python.


-- 
Steven