Problem calling math.cos()

[Robert Kern]

Sambo wrote:
> I have the following module:
> -------------------------------
> import math
> 
> def ac_add_a_ph( amp1, ph1, amp2, ph2 ):
> 
>     amp3 = 0.0 
>     ph3 = 0.0
>     ac1 = ( 0, 0j )
>     ac2 = ( 0, 0j )                                                      
>     ac3 = ( 0, 0j )
>     ac1 = complex( amp1 * math.cos( math.radians( ph1 ) ), amp1 * math.sin( math.radians( ph1 ) ) )
>     ac2 = complex( amp2 * math.cos( math.radians( ph2 ) ), amp2 * math.sin( math.radians( ph2 ) ) )
>     ac3 = ac1 + ac2
>     amp3 = math.abs( ac3 )
>     ph3 = math.atan( ac3.imag / ac3.real )
>     return [amp3, ph3]                  
> --------------------------------------
> when I import it (electronics) in python.exe in windows2000 and 
> try to use it, it croaks.  ??? 
> 
>>>>import math
>>>>import electronics
>>>>print electronics.ac_add_a_ph( 10, 0 , 6 , 45 )
> 
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
>   File "f:\devel\python\electronics.py", line 10, in ac_add_a_ph
>     ac1 = complex( amp1 * math.cos( math.radians( ph1 ) ), amp1 * math.sin( math
> .radians( ph1 ) ) )
> NameError: global name 'cos' is not defined
> 
> global?? huh?

That's not what I get.

[~]$ cat electronics.py
import math

def ac_add_a_ph( amp1, ph1, amp2, ph2 ):

    amp3 = 0.0
    ph3 = 0.0
    ac1 = ( 0, 0j )
    ac2 = ( 0, 0j )
    ac3 = ( 0, 0j )
    ac1 = complex( amp1 * math.cos( math.radians( ph1 ) ), amp1 * math.sin(
math.radians( ph1 ) ) )
    ac2 = complex( amp2 * math.cos( math.radians( ph2 ) ), amp2 * math.sin(
math.radians( ph2 ) ) )
    ac3 = ac1 + ac2
    amp3 = math.abs( ac3 )
    ph3 = math.atan( ac3.imag / ac3.real )
[~]$ python
Python 2.4.1 (#2, Mar 31 2005, 00:05:10)
[GCC 3.3 20030304 (Apple Computer, Inc. build 1666)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import electronics
>>> electronics.ac_add_a_ph(10, 0, 6, 45)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "electronics.py", line 13, in ac_add_a_ph
    amp3 = math.abs( ac3 )
AttributeError: 'module' object has no attribute 'abs'
>>>

> what does abs stand for? why is that not absolute value? hmmm.
> Hmm, complex numbers, cool I don't even have any idea where C 
> stands on this. 

Change math.abs() to abs(). It's a builtin function. Yes, it does compute the
absolute value. Fixing that:

>>> import electronics
>>> electronics.ac_add_a_ph(10, 0, 6, 45)
[14.861117513241918, 0.2895134725436232]
>>>

-- 
Robert Kern
robert.kern at gmail.com

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco