If you check the methods documentation of the Levy-stable continuous random variable you will see interval(alpha, alpha, beta, loc=0, scale=1). The problem is here that the first parameter for interval itself is named alpha and in the case of the Levy-stable distribution the first shape parameter is also called alpha. This makes it really problematic if you use keyword arguments when calling interval for a user-selected distribution. The only way out of it is renaming the the first parameter of interval or maybe less breaking is renaming the shape parameters of levy_stable.