443,760 Members | 1,644 Online Need help? Post your question and get tips & solutions from a community of 443,760 IT Pros & Developers. It's quick & easy.

# 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 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" #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 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
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 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 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, 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. I´ll try all methods to figure out the convenience of each Adolfo > Jun 27 '08 #4

 P: n/a Thank you :-), I´ll 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"

### This discussion thread is closed

Replies have been disabled for this discussion. 