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Python Math libraries - How to?

P: n/a
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 didnŽt 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"

#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
Jun 27 '08 #1
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5 Replies


P: n/a
ag************@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 didnŽt 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
--
http://mail.python.org/mailman/listinfo/python-list
Jun 27 '08 #2

P: n/a
On Mon, Apr 28, 2008 at 10:07 PM, <ag************@gmail.comwrote:
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 didnŽt 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"

#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
--
http://mail.python.org/mailman/listinfo/python-list
pi is not a global name. When you do "import math",you aren't adding
everything to the name space, you are just telling python that you are
going to be using that file. You then refer to it as math.*, such as
"math.pi", or "math.pow(r,3)". To use it the way you want to, you
would have to do "from math import pi" instead of "import math"
Jun 27 '08 #3

P: n/a
>
Thank you. IŽll try all methods to figure out the convenience of each
Adolfo
>
Jun 27 '08 #4

P: n/a
Thank you :-), IŽll do
Adolfo
>
pi is not a global name. When you do "import math",you aren't adding
everything to the name space, you are just telling python that you are
going to be using that file. You then refer to it as math.*, such as
"math.pi", or "math.pow(r,3)". To use it the way you want to, you
would have to do "from math import pi" instead of "import math"
Jun 27 '08 #5

P: n/a

"Gary Herron" <gh*****@islandtraining.comwrote in message
news:48**************@islandtraining.com...
ag************@gmail.com wrote:

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.)
|
=====================================
|
There are two good reasons for the frown.

One is for the potential conflict between builtin names, imported names
(from possibly multiple modules), and names defined in the module.
Builtins and math both have 'pow' functions that I believe are slightly
different (or maybe once were). Math and cmath have 13 functions with
duplicate names but different input and output (2.5). Importing * from
both would be disasterous.

The other is that someone not familiar with the imported module(s) will not
know where a particular name came from when reading the code. Both
problems are obvious worse with multiple imports.

Method 4: (my favorite when using multiple names from a module)

import math as m

Then use m.pi, etc.

tjr


Jun 27 '08 #6

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