Python Math libraries - How to?

[Gary Herron]

aguirre.adolfo at gmail.com wrote:
> Hi, I am a very newbie who would very much appreciate some hints.
>
> Python 2.52. on Windows XP for now. Soon on Ubuntu 8
>
> I am teaching myself Python following free tutorials. I can solve
> problems using arithmetic, but when I try to upgrade the programs
> using math libraries nothing seems to work. I downloaded a 2002
> tutorial from Zelle "An Introduction to Computer Science" where he
> uses a "import math" statement to calculate a square root. I tried the
> "pi" library function but it didn´t work. I tried using def Pi()  it
> did not work either. I am yet to find a tutorial that explains how to
> declare (or initialize) and pass numbers to the functions such as
> "cos(x)" and the pi which does not have a variable in it. Is just a
> constant.
>
> Here is the arithmetic program I made that it worked before I added
> the "import math" line.  I  erased the constant p = 3.1416 and added
> the "i" for the library function "pi" in the algorithms. But I get an
> error message not recognizing "pi"
>   

You have several ways to import a module, and your choice determines how 
you access things.

Method 1:

import math

Then use:  math.pi, math.sqrt, math.sin, math.cos, ...

Method 2:

from math import pi, sqrt

Then use pi, and sqrt.
But other module attributes (like sin, and cos) are not accessible.


Method 3:

from math import *

Then use pi, sqrt, cos, sin, and anything else defined by the module.
(This is sometime  frowned upon, but there's no reason to do so here.)

Gary Herron



>
>
> #volumen.py
> # A program to compute the volume and surface area of a sphere
> import math
>
> def main():
>
>     print "This program calculates the volume and surface area of a
> sphere"
>     print
>     r = input("Please enter the radious: ")
>     print
>     r3 = r*r*r
>     volume = 4/3*pi*r3
>     r2 = r*r
>     surface = 4*pi*r2
>     print "The Volume is", volume, " Cubic centimeters"
>     print
>     print "The Surface area is", surface, " square centimeters"
>
> main()
>
> *** Error message *************
>
> Traceback (most recent call last):
>   File "C:/Python25/z - MIS PROGRAMAS/volumen-b.py", line 20, in
> <module>
>     main()
>   File "C:/Python25/z - MIS PROGRAMAS/volumen-b.py", line 13, in main
>     volume = 4/3*pi*r3
> NameError: global name 'pi' is not defined
> --
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>