Search for a value in a list in Python

Question

I'm using Python to search for the position of an entered name in a list. I use the binary search: compare entered name with the middle-value of the list, if not matched, search in the 1st half list then 2nd half list. When I run following script, IDE shows nothing. Please help me review it:

def search_for_name(name, list):
  midValue = list[int(len(list)/2)]
  x = 0
  if name == midValue:
    x = int(len(list)/2)
    return x
  elif name < midValue:
    while x < int(len(list))/2:
      if list[x] == name:
        return x
      else:
        x += 1
  else:
    x = int(len(list)/2)
    while x <= int(len(list)):
      if list[x] == name:
        return x
      else:
        x += 1
  print('The name you want to search exists in our list. Its position is {}'.format(x))

Why would it show anything? It's just a function definition. — Kelly Bundy, Mar 12 '20 at 14:07
Is your list ordered? If not, a binary search doesn't really make much sense. — LLSv2.0, Mar 12 '20 at 14:07
just use list.find('name to be searched') it give the index position — Hari, Mar 12 '20 at 14:08
@Hari: That's `O(n)`; proper binary search is `O(log n)` (though this implementation isn't binary search, it's just splitting the linear search in half once). — ShadowRanger, Mar 12 '20 at 14:09
@ShadowRanger Nah, it's O(1), thanks to `AttributeError: 'list' object has no attribute 'find'`. — Kelly Bundy, Mar 12 '20 at 14:10
Does this answer your question? [Finding the index of an item in a list](https://stackoverflow.com/questions/176918/finding-the-index-of-an-item-in-a-list) — Jan Giacomelli, Mar 12 '20 at 14:10

score 1 · Answer 1 · answered Mar 12 '20 at 14:09

1

You're returning the found value from the function, which means that your print statement will never be called. Instead, use the value returned and then print that:

def search_for_name(name, list):
    ...

pos = search_for_name('matt', ['a', 'b', 'matt', 'x', 'y', 'z'])

if pos is None:
    print("Name was not found")
else:
    print('The name you want to search exists in our list. Its position is {}'.format(pos))

answered Mar 12 '20 at 14:09

MatsLindh

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`f"Its position is {pos}."` – Guimoute Mar 12 '20 at 14:12
As long as you're on 3.6, definitely! – MatsLindh Mar 12 '20 at 14:20

Search for a value in a list in Python

1 Answers1