How to do nested loop in python

Question

I would like to do nested loop in my programming. However, this code did not meet my expectation.

X=[0,1,1,1,0]

length=len(X)
for i,val in enumerate(X):
    a=0
    count=0
    while (count<length):
        a=15+a
        print (a)
        HWPQ=np.matrix([[1, 0, 0, 0], [0, math.cos(4*math.radians(a)), 
        math.sin(4*math.radians(a)), 0], [0, math.sin(4 * math.radians(a)), - 
        math.cos(4 * math.radians(a)), 0], [0, 0, 0, -1]])
        result=HWPQ*val
        print (result)
        count=count +1
    print ("\n")

Supposedly, in this program, I would like to update the value of a for each element using the loop. For example:

X=0 for a=0
X=1 for a=15
X=1 for a=30
X=1 for a=45
X=0 for a=60

The result should be, as I calculated it manually:

[[ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]]
[[ 1.         0.         0.         0.       ]
 [ 0.         0.5        0.8660254  0.       ]
 [ 0.         0.8660254 -0.5        0.       ]
 [ 0.         0.         0.        -1.       ]]
[[ 1.         0.         0.         0.       ]
 [ 0.        -0.5        0.8660254  0.       ]
 [ 0.         0.8660254  0.5        0.       ]
 [ 0.         0.         0.        -1.       ]]
[[  1.00000000e+00   0.00000000e+00   0.00000000e+00   0.00000000e+00]
 [  0.00000000e+00  -1.00000000e+00   1.22464680e-16   0.00000000e+00]
 [  0.00000000e+00   1.22464680e-16   1.00000000e+00   0.00000000e+00]
 [  0.00000000e+00   0.00000000e+00   0.00000000e+00  -1.00000000e+00]]
 [[ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]]

What's X used in this code? Seems useless? a just a arithmetic progression, ignore any value of X — atline
– atline, Commented Jul 27, 2018 at 3:11
Is that last one correct? you're multiplying your matrix by val, which is 0, so the whole matrix would be 0s. — i alarmed alien
– i alarmed alien, Commented Jul 27, 2018 at 3:11
@ i alarmed alien. You are correct. I have updated the last output. — Afir
– Afir, Commented Jul 27, 2018 at 3:14
@atline. The value of X is represented as list of bit 0 or 1. — Afir
– Afir, Commented Jul 27, 2018 at 3:16

i alarmed alien · Accepted Answer · 2018-07-27 03:15:24Z

There seem to be a load of unnecessary variables in your code, like count, X, and i. Removing them and using a standard for loop, you get:

X=[0,1,1,1,0]
a=0
for val in X:
    print (a)
    HWPQ=np.matrix([
        [1, 0, 0, 0], 
        [0, math.cos(4*math.radians(a)), math.sin(4*math.radians(a)), 0], 
        [0, math.sin(4 * math.radians(a)), - math.cos(4 * math.radians(a)), 0],
        [0, 0, 0, -1]])
    result=HWPQ*val
    print (result)
    a=15+a
    print ("\n")

which creates the output that you want.

0
[[ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]]


15
[[ 1.         0.         0.         0.       ]
 [ 0.         0.5        0.8660254  0.       ]
 [ 0.         0.8660254 -0.5        0.       ]
 [ 0.         0.         0.        -1.       ]]


30
[[ 1.         0.         0.         0.       ]
 [ 0.        -0.5        0.8660254  0.       ]
 [ 0.         0.8660254  0.5        0.       ]
 [ 0.         0.         0.        -1.       ]]


45
[[  1.00000000e+00   0.00000000e+00   0.00000000e+00   0.00000000e+00]
 [  0.00000000e+00  -1.00000000e+00   1.22464680e-16   0.00000000e+00]
 [  0.00000000e+00   1.22464680e-16   1.00000000e+00   0.00000000e+00]
 [  0.00000000e+00   0.00000000e+00   0.00000000e+00  -1.00000000e+00]]


60
[[ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]
 [ 0.  0.  0.  0.]]

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