Actions

Python examples

From AstroEd

Revision as of 07:08, 7 February 2013 by WikiSysop (talk | contribs) (= Writing an executable program)

This page contains examples and links to programs used for our Research Methods - Programming with Python short course.

Very simple Python

Start a Python interactive session using the "python" command to get a >>> prompt.

Command line use

There are many built-in features of Python that are described in the documentation, but to get started let's do something very easy.

Type

>>>x=1

and then simply

>>>x

and you'll see

1


Type

>>>x=1.01

and then after you type "x" you'll see

>>>x
1.01


Clearly you have a real-time calculator in hand, so try something more exciting.

>>>x=1.01
>>>y=1.0001
x/y

and you'll see something like this

1.0098990100989902

Modify that with

>>>z=x/y
>>>z

and you'll see the same result. But now try

>>>int(z)

and you'll see

1


That is, the function int() took the integer part of z. You can put that in another variable such as

>>>a=int(z)
>>>a
1

Curiously, a seems to be an integer. It is said to be dymanically typed in this assignment. That can change. If you now add a little bit to a you'll see it turns into a floating point number

>>>a = a + 0.001
>>>a
1.001

Importing math

There's much more you can do, of course, but you need to import the math functions first. Here's one way to do that.

>>>import math

Now try

>>>math.pi

and you'll see

3.141592653589793

The functions in the math package need the "math." in front of them.

>>>math.sin(math.pi/4.)

returns

0.7071067811865475

as does

>>>math.sqrt(0.5)

Similarly

>>>4.*math.asin(math.sqrt(0.5))

returns

3.1415926535897936

The comprehensive list of math functions is on the Python documentation site. You can try out some of the more exotic possibilities on your own.


Writing an executable program