Myujth

I was asked to define a recursive function that takes in two parameters:

• n



• 
  

  valmax

  
  
  

  and returns a list of n numbers picked randomly from the interval [0 , valmax]

  
  

`

import random

def random_list(n, valmax, lst = ):
 """
 parameters : n of type int;
 valmax of type int;
 returns : a list of n numbers picked randomly from the interval 
 [0, valmax]
 """
 if len(lst) == n: 
 return lst
 return [random.randint(0, valmax)] + random_list(n, valmax)

print(random_list(10,100))`

However, I'm getting an

RecursionError

How can I fix my code so that it returns a list with n random numbers in the interval [0, valmax] ?

Your logic is wrong. You need each function call to return n random integers, so you do not need to pass it in a list.

Each function generates a single random number in the range [0, valmax] and concatenates it to the random list of integers which is of length one less (n-1) which it gets from calling itself recursively.

The base case is when n == 1, in which case we return an empty list.

import random
def random_list(n, valmax):
 if n == 0:
 return 
 return [random.randint(0, valmax)] + random_list(n-1, valmax)

and a test:

random_list(10, 20)
#[20, 9, 4, 7, 3, 4, 3, 18, 19, 9]

Instead of keeping a default parameter (which can also cause unexpected behavior on consecutive calls), use yield for a cleaner solution. Also, simply use random.randint(0, valmax) to generate a single random integer between 0 and valmax:

import random
def random_list(n, valmax):
 if n:
 yield random.randint(0, valmax)
 yield from random_list(n-1, valmax)

print(list(random_list(10, 10))) #create a list of length ten with random values between 0 and 10, inclusive.

Output:

[4, 6, 9, 1, 10, 2, 2, 8, 2, 10]

You could write a generic build_list function -

import random

def identity (x):
 return x

def build_list (size, proc = identity):
 if size == 0:
 return 
 else:
 return build_list (size - 1, proc) + [ proc (size - 1) ]

print (build_list (5))
# [ 0, 1, 2, 3, 4 ]

print (build_list (5, lambda _: random.randint (0, 10)))
# [ 4, 7, 7, 3, 6 ]

random_list could be a specialization of build_list -

def random_list (size, valmax):
 return build_list (size, lambda _: random.randint (0, valmax))

print (random_list (5, 10))
# [ 1, 7, 4, 7, 0 ]