Searching a list with bisect

HiHe 3 Tallied Votes 632 Views Share

Explore the Python module bisect to search a sorted list and insert elements in the proper location in a sorted list.

''' bisect_search.py
If a list is long and sorted, then a binary search is faster
than a list index() search.
works with Python27 and Python32  HiHe
'''

import bisect

def linear_search(names, search):
    """
    a standard linear search
    """
    ix = names.index(search)
    sf = "Linear search for {}, found it at index {}"
    print(sf.format(search, ix))
    
def bisect_search(names, search):
    """
    search using bisect()
    no-match gives closest index (no index error)
    """
    ix = bisect.bisect(names, search) - 1
    sf = "Bisect search for {}, found it at index {}"
    # this will trap the no-match situation
    if names[ix] == search:
        print(sf.format(search, ix))
    else:
        print("{} not found!".format(search))

names = [
'Pam', 'Zoe', 'Dee', 'Eva', 'Gin', 'Ivy', 'Kay', 'Amy', 'Moe'
]
# bisect search needs a sorted list
names.sort()
print(names)
print('-'*70)

search = 'Kay'

linear_search(names, search)

print('-'*70)

bisect_search(names, search)

print('-'*70)

# search for a name not in the list
search = 'Lisa'
bisect_search(names, search) 

print('-'*70)

# you can insert a name into the sorted name list at the proper spot
new_name = 'Mae'
bisect.insort_left(names, new_name)
print(names)   # testing

''' output >>>
['Amy', 'Dee', 'Eva', 'Gin', 'Ivy', 'Kay', 'Moe', 'Pam', 'Zoe']
----------------------------------------------------------------------
Linear search for Kay, found it at index 5
----------------------------------------------------------------------
Bisect search for Kay, found it at index 5
----------------------------------------------------------------------
Lisa not found!
----------------------------------------------------------------------
['Amy', 'Dee', 'Eva', 'Gin', 'Ivy', 'Kay', 'Mae', 'Moe', 'Pam', 'Zoe']
'''
TrustyTony 888 ex-Moderator Team Colleague Featured Poster

Related code of mine to help the Dani's related article search:
http://www.daniweb.com/software-development/python/code/436392/example-of-bisection-search-for-monotonously-increasing-function-value

There we do the bisection mathematically from function instead of ready value list.

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