How variables are declared in python?

Question

I guess something is wrong with this I believe. I have an array of data set I'm trying to perform some analysis on. This is what I want to do. Say for example the following is the array

signal=[1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1...] , I want to take the data points 0:3 stored somewhere, I need them and also replace those 0:3 with zeros. This is how I did it but the final result comes out right but the stored 0:3 data points stored also come out to be zeros. Can anyone help me out here. I thought it was something simple to do but I have been battling with this for the past couple of days. Thanks in advance!

here is my code:

n = len(signal)

for i in range(n):

    first_3points = signal[0:3]

    signal[0:3] = 0

    trancated_signal = signal

I will be very glad to see where I went wrong!

Answer 1

It looks like your application is better served with numpy, which is well-developed to work with arrays representing signal samples. You may already be using numpy, since if signal is a list, the assignment signal[0:3] = 0 raises a TypeError . Here's how I'd do it using numpy:

import numpy as np
N = 256
signal = np.ones(N)
first3 = signal[0:3].copy()
signal[0:3] = 0

Note that if you don't make first3 a copy of the first elements in signal , it just becomes a view into signal , and when you change elements in signal , you also change first3 . If I understand your question correctly, you are trying to save the original elements from signal in first3 before you change them.

Answer 2

Using ordinary lists instead of numpy this is quite simple:

signal = [1] * 20
first_3_points = signal[:3]
signal[:3] = [0] * 3

The loop in your original code appears to be unnecessary.