Python generate random number in specific range

I'm a beginner and learning Python for 2 Months.

I need to generate random 5 float numbers in range [-1,1] and normalize it. The sum of this random numbers has to be always 1. It's quite important.

a = np.random.random(5)*2 -1 #generate 5 numbers in range [-1,1] 

But how to make the sum of them = 1?

a /= np.sum(a) # Doesn't work

I need some help.