Python 数据结构代码示例(一)

上一篇文章SONiC 中的 Python 编程中提到了 Python 的具体应用，为了打好基础，我们先复习一下 Python 内置的数据结构，并编写一些示例代码，展示一下如何使用他们。

List 列表, Tuple 元组和Range范围

List是一种序列类型(Sequence Types), 它包含List，Tuple和Range，序列类型支持一些通用操作：

Operation	Result
x in s	True if an item of s is equal to x, else False
x not in s	False if an item of s is equal to x, else True
s + t	the concatenation of s and t
s * n or n * s	equivalent to adding s to itself n times
s[i]	ith item of s, origin 0
s[i:j]	slice of s from i to j
s[i:j:k]	slice of s from i to j with step k
len(s)	length of s
min(s)	smallest item of s
max(s)	largest item of s
s.index(x[, i[, j]])	index of the first occurrence of x in s (at or after index i and before index j)
s.count(x)	total number of occurrences of x in s

List是可修改序列类型(mutable Sequence Types)，而Tuple和Range是不可修改序列类型(Immutable Sequence Types)，不可修改意味着元素个数在定义以后不可改变，元素内容也不可改变，所以Tuple和Range功能要比List少很多。

下表是List支持的一些操作

Operation	Result
s[i] = x	item i of s is replaced by x
s[i:j] = t	slice of s from i to j is replaced by the contents of the iterable t
del s[i:j]	same as s[i:j] = []
s[i:j:k] = t	the elements of s[i:j:k] are replaced by those of t
del s[i:j:k]	removes the elements of s[i:j:k] from the list
s.append(x)	appends x to the end of the sequence (same as s[len(s):len(s)] = [x])
s.clear()	removes all items from s (same as del s[:])
s.copy()	creates a shallow copy of s (same as s[:])
s.extend(t) or s += t	extends s with the contents of t (for the most part the same as s[len(s):len(s)] = t)
s *= n	updates s with its contents repeated n times
s.insert(i, x)	inserts x into s at the index given by i (same as s[i:i] = [x])
s.pop() or s.pop(i)	retrieves the item at i and also removes it from s
s.remove(x)	removes the first item from s where s[i] is equal to x
s.reverse()	reverses the items of s in place

List的初始化 fruit = [‘apple’, ‘banana’]

Tuple的初始化 month = (‘Jan’,’Feb’)

范围的初始化 r = range(0, 20, 2)

可以通过range给list初始化

list(range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
list(range(1, 11))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
list(range(0, 30, 5))
[0, 5, 10, 15, 20, 25]

关于 List 的一些示例代码

fruits = ['orange', 'apple', 'pear', 'banana', 'kiwi', 'apple', 'banana']
fruits.count('apple')
2
fruits.count('tangerine')
0
fruits.index('banana')
3
fruits.index('banana', 4)  # Find next banana starting at position 4
6
fruits.reverse()
fruits
['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange']
fruits.append('grape')
fruits
['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange', 'grape']
fruits.sort()
fruits
['apple', 'apple', 'banana', 'banana', 'grape', 'kiwi', 'orange', 'pear']
fruits.pop()
'pear'

关于Tuple的一些示例代码

t = 12345, 54321, 'hello!'
t[0]
12345
t
(12345, 54321, 'hello!')
# Tuples may be nested:
u = t, (1, 2, 3, 4, 5)
u
((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))
# Tuples are immutable:
t[0] = 88888
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
# but they can contain mutable objects:
v = ([1, 2, 3], [3, 2, 1])
v
([1, 2, 3], [3, 2, 1])

一个示例程序：统计一段文本中单词个数，并输出频率最高的指定个数，比如 Top 10。

#!/bin/python3

import string

sym = string.punctuation

def is_separator(c):
    if c.isspace():
        return True
    if c in sym:
        return True
    return False

def word_freq_count():
    words = []
    freqs  = []
    tops = []
    text = 'this is a test text,it contain little words but for test ok,what do you think about it?,it is a question?'
    print(text)
    s = 0
    e = 0
    m = 0
    for c in text:
        e = m
        if is_separator(c):
            w = text[s:e]
            if is_separator(w):
                m += 1
                s += 1
                continue
            p = words.count(w)
            if p > 0:
                i = words.index(w)
                freqs[i] += 1
                tops[i] += 1
            else:
                words.append(w)
                freqs.append(1)
                tops.append(1)
            s = e + 1
        m += 1
    print(words)
    print(freqs)
    print(tops)
    tops.sort(reverse=True)
    i = freqs.index(tops[0])
    print(words[i])
    print(tops[0])

word_freq_count()

参考资料：

1. https://docs.python.org/3/library/stdtypes.html
2. https://docs.python.org/3/tutorial/datastructures.html