I wanted to fit a power law function to data, not a polynomial. Here's how I did it.
I used the least squares method.
If you prefer other types of functions, just change the function form to whatever you want to fit when you define it.
The inputs for leastsq are the error function (difference between data and a function you want to fit) and initial conditions. When full_output = nonzero, it returns the covariance matrix in addition to the parameters that minimize the sum of squares of the error function.
What would you fit a power law function to?