1. Managing Ordered Sequences with bisect
The bisect module offers two main functions --- bisect and insort --- that use the binary serach algorithm to quickly find and insert items in any sorted sequence.
Example 2-17. bisect finds insertion points for items in a sorted sequence.
import bisect
import sys
HAYSTACK = [1, 4, 5, 6, 8, 12, 15, 20, 21, 23, 23, 26, 29, 30]
NEEDLES = [0, 1, 2, 5, 8, 10, 22, 23, 29, 30, 31]
ROW_FMT = '{0:2d} @ {1:2d} {2}{0:<2d}'
def demo(bisect_fn):
for needle in reversed(NEEDLES):
position = bisect_fn(HAYSTACK, needle)
offset = position * ' |'
print(ROW_FMT.format(needle, position, offset))
if __name__ == "__main__":
if sys.argv[-1] == "left":
bisect_fn = bisect.bisect_left
else:
bisect_fn = bisect.bisect
print('DEMO:', bisect_fn.__name__)
print('haystack ->', ' '.join("%2d" % n for n in HAYSTACK)) # 注意此处 join 的用法： join 中没有用列表[] 符号
demo(bisect_fn)
"""
# 输出： 脚本不加参数
NEO:ch2-array-of-sequences zhenxink$ python3 search_with_bisect.py
DEMO: bisect
haystack -> 1 4 5 6 8 12 15 20 21 23 23 26 29 30
31 @ 14 | | | | | | | | | | | | | |31
30 @ 14 | | | | | | | | | | | | | |30
29 @ 13 | | | | | | | | | | | | |29
23 @ 11 | | | | | | | | | | |23
22 @ 9 | | | | | | | | |22
10 @ 5 | | | | |10
8 @ 5 | | | | |8
5 @ 3 | | |5
2 @ 1 |2
1 @ 1 |1
0 @ 0 0
# 输出： 脚本加参数 left
NEO:ch2-array-of-sequences zhenxink$ python3 search_with_bisect.py left
DEMO: bisect_left
haystack -> 1 4 5 6 8 12 15 20 21 23 23 26 29 30
31 @ 14 | | | | | | | | | | | | | |31
30 @ 13 | | | | | | | | | | | | |30
29 @ 12 | | | | | | | | | | | |29
23 @ 9 | | | | | | | | |23
22 @ 9 | | | | | | | | |22
10 @ 5 | | | | |10
8 @ 4 | | | |8
5 @ 2 | |5
2 @ 1 |2
1 @ 0 1
0 @ 0 0
"""
Example 2-18: Given a test score, grades returns the corresponding letter grade. (bisect 的一个应用例子)
import bisect
def grade(score, breakpoints=[60, 70, 80, 90], grades='FDCBA'):
i = bisect.bisect(breakpoints, score)
return grades[i]
letter_grade = [grade(score) for score in [33, 99, 77, 70, 89, 90, 100]]
print(letter_grade)
# 输出：
# ['F', 'A', 'C', 'C', 'B', 'A', 'A']
insort(seq, item) inserts items into seq so as to keep seq in ascending order.
Example 2-19: Insort keeps a sorted sequence always sorted.
import bisect
import random
SIZE = 7
random.seed(1729)
my_list = []
for i in range(SIZE):
new_item = random.randrange(SIZE * 2)
bisect.insort(my_list, new_item)
print("%2d ->" % new_item, my_list)
'''
# 输出：
10 -> [10]
0 -> [0, 10]
6 -> [0, 6, 10]
8 -> [0, 6, 8, 10]
7 -> [0, 6, 7, 8, 10]
2 -> [0, 2, 6, 7, 8, 10]
10 -> [0, 2, 6, 7, 8, 10, 10]
'''
# bisect.insort keeps a sorted sequence always sorted.
bisect 模块参数链接：https://www.cnblogs.com/skydesign/archive/2011/09/02/2163592.html
2. Array
If the list will only contain numbers, an array.array is more efficient than a list : array supports all mutable sequence operations(including .pop, .insert, and .extend), and additional methods for fast loading and saving such as .frombytes and .tofile .
Example 2-20. Creating , saving, and loading a large array of floats.
from array import array
from random import random
floats = array('d', (random() for i in range(10 ** 7)))
# create an array of double-precision floats(typecode 'd') from any iterable
# object -- in this case, a generator expression.
print(floats[-1])
with open("floats.bin", "wb") as fp:
floats.tofile(fp)
floats2 = array('d') # create an empty array of doubles.
with open("floats.bin", "rb") as fp:
floats2.fromfile(fp, 10 ** 7)
# array.fromfile(f, n) ---> Read n objects from the file object f and append them to the end of the array.
print(floats2[-1])
print(floats == floats2)
"""
输出结果：
0.31630082281843985
0.31630082281843985
True
"""
array 用法链接： https://blog.csdn.net/xc_zhou/article/details/88538793
end
来源：https://www.cnblogs.com/neozheng/p/12151052.html