Problem calling math.cos()

[Alex Martelli]

Sambo <sambo at void.com> 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 )

You're defining ac1, ac2, ac3 as tuples, each with two items.  That's
silly: remove these three useless and confusing lines (the first two are
prety silly too).  No damage, but, avoidable extra confusion.

>     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 ) ) )

[[some lines split to respect NNTP's constraint on 80-char lines]]

> NameError: global name 'cos' is not defined
> >>>
> 
> 
> global?? huh?

Weird -- I can't reproduce this; it's the kind of symptom you get when
mistakenly using a comma instead of a dot, for example, but I don't see
that error in your code.

What I _do_ see is an "AttributeError: 'module' object has no attribute
'abs'" on the amp3 assignment -- of course, because that's indeed the
fact (abs is a builtin, not a member to module math).

Most likely, you got a bit confused and didn't copy-and-paste exactly
what was going on.


> what does abs stand for? why is that not absolute value? hmmm.

abs does stand for absolute-value.

> Hmm, complex numbers, cool I don't even have any idea where C 
> stands on this. 

C has no stand on complex numbers.


Alex