find index of first non-negative value in a sorted list

find_first_nonnegative.py

def split(x):
  """return the index of the first non-negative value in a sorted list:
  legend for comments: 
  "-" stands for negative
  "+" stands for non-negative
  """
  # check for corner cases:
  if len(x)==0:
     return 0
  elif len(x)==1:
     return 1

  ind = len(x)//2
  if (x[ind]>=0) and ((x[ind-1] < 0)):
    # .......-|+.......
    return ind
    
  elif (x[ind]>=0) and ((x[ind-1] >= 0)):
    # ......+|+......
    # descend into the left side
    return split(x[:ind])
    
  elif x[ind]<0:
    # .....-|-.......
    # descend into the right
    return ind + split(x[ind:])

# corner case: only non-negatives
seq = list(range(0,10))
ind = split(seq)
print(ind) # -> 0

# corner case: only negatives
seq = list(range(-10,0))
ind = split(seq)
print(ind) . # -> 10

# regular cases
import random

for _ in range(20):
    seq = sorted([random.randint(-100, 100) for _ in range(10)])
    ind = split(seq)
    assert (seq[ind-1]<0) and(seq[ind]>=0)
    print(seq[ind-1],'|', seq[ind])