I would like to know if in Python, and more precisely, in lmfit library, there is an option for fitting data by parts ? I would like to fit data defined in different ranges and then obtain a unique fit.
Thank you
Without a more concrete example, it is hard to give a concrete answer. But, if I understand your question correctly, you are looking to do a fit to one specific region of your data, then a fit (probably with a different functional form) to another region of your data, and then perhaps combine the multiple regions to get a final fit.
If that is correct, then yes, this can be done with lmfit (and probably with other libraries as well). Let's say you want to fit data that is sort of peak like with an exponential decaying background. First, isolate a region around that peak (it doesn't have to be perfect) and fit a peak (say, Gaussian to that). Then fit an exponential decay to all the data except the peak area. (Aside: numpy.where can be very useful in identifying the regions). Finally, combine the two and fit the whole curve to peak + background.
If that is too vague and doesn't point you in the right direction, please make the question more specific.