Finding if data in array is periodic

1. How do you know if data is periodic?
2. How do you check if something is not in a list Python?

How do you know if data is periodic?

Transform the data into frequency domain using the discrete Fourier transform (DFT). If the data is perfectly periodic, there will be exactly one frequency bin with a high value, and other bins will be zero (or near zero, see spectral leakage).

How do you check if something is not in a list Python?

“not in” operator − This operator is used to check whether an element is not present in the passed list or not. Returns true if the element is not present in the list otherwise returns false.