A reasonably robust binary search *with unit tests*

binary_search.py

from typing import List, Tuple
import pytest


def binary_search(desired_member:Tuple[int, float], sorted_list:List[Tuple[int, float]]) -> int:
  """perform binary search over sorted list, return index of desired member"""

  # check parameter type
  if not (type(desired_member) is int or type(desired_member) is float):
    raise TypeError("desired_member must be a number")
  if not all(type(n) is int or type(n) is float for n in sorted_list):
    raise TypeError("sorted list members must all be numbers")

  # check boundaries
  value_error_message = "desired_member not in sorted list"
  if desired_member > sorted_list[-1] or desired_member < sorted_list[0]:
    raise ValueError(value_error_message)

  list_len = len(sorted_list)
  prev_idx = 0
  idx = int(list_len / 2)
  selected_member = sorted_list[idx]
  while selected_member != desired_member:
    last_step = idx - prev_idx
    prev_idx = idx
    new_step = abs(int(last_step/2))
    if new_step == 0:
      new_step = 1
    if selected_member > desired_member:
      if (last_step == 1):
        raise ValueError(value_error_message)
      idx -= new_step
    else:
      if (last_step == -1):
        raise ValueError(value_error_message)
      idx += new_step 
    selected_member = sorted_list[idx]
  return idx


# TESTS

test_list = [i * 2 + 1 for i in range(1024)]

def test_binary_search_finds_correct_index():
  for i, target in enumerate(test_list):
    assert i == binary_search(target, test_list)

def test_binary_search_raises_value_error_when_target_not_in_search_list():
  targets = [0, 2, 4, 32, 48, 1024, 1026, 2046, 2048, 2050]
  for t in targets:
    with pytest.raises(ValueError):
      binary_search(t, test_list)

def test_binary_search_raises_type_error_when_arg_not_numeric():
  targets = ["1", True]
  for t in targets:
    with pytest.raises(TypeError):
      binary_search(t, test_list)
  with pytest.raises(TypeError):
    binary_search("2", list("0123456"))

def test_binary_search_works_for_floats():
  float_list = [float(n) for n in test_list]
  for i, target in enumerate(test_list):
    assert i == binary_search(target, test_list)
  targets = [-1.1, 1.1, 3.1, 48.1, 513.1, 2048.9, 2049.3]
  for t in targets:
    with pytest.raises(ValueError):
      binary_search(t, test_list)

# RUN THE TESTS
# in a build script, we would use `python -m pytest path/to/dir_with_tests` to run the whole suite
test_binary_search_finds_correct_index()
test_binary_search_raises_value_error_when_target_not_in_search_list()
test_binary_search_raises_type_error_when_arg_not_numeric()
test_binary_search_works_for_floats()