Signals in the real world often have a periodic nature. A commonly used tool to deal with these signals is the Discrete Fourier transform (see https://en.wikipedia.org/wiki/Discrete-time_Fourier_transform). The Discrete Fourier transform is a transformation from the time domain into the frequency domain, that is, the linear decomposition of a periodic signal into sine and cosine functions with various frequencies:

Functions for Fourier transforms can be found in the scipy.fftpack module (NumPy also has its own Fourier package numpy.fft). Included in the package are Fast Fourier transforms, differential and pseudo-differential operators, as well as several helper functions. MATLAB users will be pleased to know that a number of functions in the scipy.fftpack module have the same name as their MATLAB counterparts, and a similar function as their MATLAB equivalents.