Random Number Generator: Exponential Distribution

The probability distribution function of Exponential distribution with positive constant $\lambda$ is \[ P(x)= \begin{cases} \lambda{e}^{-\lambda x} & x \geq 0 \\ 0 & x \lt 0 \end{cases} \] To generate a random number $X$ from Exponential distribution with constant $\lambda$,
a random number $r$ between $0$ and $1$ is drawn.
then $X$ can be generated by the formula \[ X=-\frac{1}{\lambda} \ln(1-r) \]

Distribution constant ($\lambda$) :

#input VALUE = #value#; print() # retrive data a = VALUE[0] if not (a > 0): show("Please input a proper constant of distribution.") assert() def Generate(): #draw a random number r and calculate X R = randint(0, 99) r = R/100 X = -1/a*log(1-r) #display result show(html('Random number $r$ drawn: 0.'+ str(R))) show(html('Corresponding $X$: '+ str(n(X,digits=4)))) @interact def _(action=selector(['Generate'],buttons=True)): eval(action + "()")