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Python examples

From AstroEd

Revision as of 06:59, 7 February 2013 by WikiSysop (talk | contribs) (= Command line math)

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 math

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