Searching a sorted list? [closed]

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.

---

We don’t allow questions seeking recommendations for books, tools, software libraries, and more. You can edit the question so it can be answered with facts and citations.

Closed 4 years ago.

开发者_C百科 Improve this question

What is a Pythonic way to search or manipulate sorted sequence?

---

bisect is part of the standard library - is that the sort of thing you're looking for?

---

It's worth noting that there are a couple high-quality Python libraries for maintaining a sorted list which also implement fast searching: sortedcontainers and blist. Using these depends of course on how often you're inserting/removing elements from the list and needing to search. Each of those modules provide a SortedList class which efficiently maintains the items in sort order.

From the documentation for SortedList:

L.bisect_left(value)
    Similar to the bisect module in the standard library, this returns
    an appropriate index to insert value in L. If value is already present
    in L, the insertion point will be before (to the left of) any existing
    entries.

L.bisect(value)
    Same as bisect_left.

L.bisect_right(value)
    Same as bisect_left, but if value is already present in L, the
    insertion point will be after (to the right of) any existing entries.

Both implementations use binary search to find the correct index of the given value. There's a performance comparison page for choosing between the two modules.

Disclaimer: I am the author of the sortedcontainers module.

---

Python:

import bisect

def find_in_sorted_list(elem, sorted_list):
    # https://docs.python.org/3/library/bisect.html
    'Locate the leftmost value exactly equal to x'
    i = bisect.bisect_left(sorted_list, elem)
    if i != len(sorted_list) and sorted_list[i] == elem:
        return i
    return -1

def in_sorted_list(elem, sorted_list):
    i = bisect.bisect_left(sorted_list, elem)
    return i != len(sorted_list) and sorted_list[i] == elem

L = ["aaa", "bcd", "hello", "world", "zzz"]
print(find_in_sorted_list("hello", L))  # 2
print(find_in_sorted_list("hellu", L))  # -1
print(in_sorted_list("hellu", L))       # False