Python 数据结构,,1 列表方法list
Python 数据结构,,1 列表方法list
1 列表方法
list.append(x) # 添加一个元素xlist.extend(L) # 添加L列表中的所有元素list.insert(i,x) # 在列表指定位置插入一个元素list.remove(x) # 删除列表中值为x的元素list.pop(i) # 删除列表中指定位置的元素并返回元素值list.clear() # 清空列表list.index(x) # 返回列表中第一个值为x的元素索引list.count(x) # 返回列表中x出现的次数list.sort() # 对列表进行排序list.reverse() # 返回列表元素的逆序排列list.copy() # 浅拷贝
1.1 列表用作堆栈
用 append() 添加元素,pop() 取出元素。
stack = [3, 4, 5]stack.apppend(6)stack.pop()
1.2 列表用作队列
from collections import dequequeue = deque(["Eric", "John", "Michael"])queue.append("Terry")queque.popleft()
1.3 列表推导式
# 普通方法squares = []for x in range(10): squares.append(x**2)# 列表推导式squares = list(map(lambda x: x**2, range(10)))squares = [x**2 for x in range(10)]
一些例子:
>>> vec = [-4, -2, 0, 2, 4]>>> # create a new list with the values doubled>>> [x*2 for x in vec][-8, -4, 0, 4, 8]>>> # filter the list to exclude negative numbers>>> [x for x in vec if x >= 0][0, 2, 4]>>> # apply a function to all the elements>>> [abs(x) for x in vec][4, 2, 0, 2, 4]>>> # call a method on each element>>> freshfruit = [‘ banana‘, ‘ loganberry ‘, ‘passion fruit ‘]>>> [weapon.strip() for weapon in freshfruit][‘banana‘, ‘loganberry‘, ‘passion fruit‘]>>> # create a list of 2-tuples like (number, square)>>> [(x, x**2) for x in range(6)][(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25)]>>> # the tuple must be parenthesized, otherwise an error is raised>>> [x, x**2 for x in range(6)] File "<stdin>", line 1, in ? [x, x**2 for x in range(6)] ^SyntaxError: invalid syntax>>> # flatten a list using a listcomp with two ‘for‘>>> vec = [[1,2,3], [4,5,6], [7,8,9]]>>> [num for elem in vec for num in elem][1, 2, 3, 4, 5, 6, 7, 8, 9]
列表表达式还支持更复杂的表达式和嵌套函数:
from math import pi[str(round(pi, i)) for i in range(1, 6)]
1.4 嵌套的列表表达式
matrix = [ [1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12],]# 交换行与列[[row[i] for row in matrix] for i in range(4)]# s使用zip()函数list(zip(*matrix))
2 del语句
按照索引删除指定的值
>>> a = [-1, 1, 66.25, 333, 333, 1234.5]>>> del a[0]>>> a[1, 66.25, 333, 333, 1234.5]>>> del a[2:4]>>> a[1, 66.25, 1234.5]>>> del a[:]>>> a[]
del 也可以删除整个变量:
>>> del a
3 元组和序列
4 集合
>>> basket = {‘apple‘, ‘orange‘, ‘apple‘, ‘pear‘, ‘orange‘, ‘banana‘}>>> print(basket) # show that duplicates have been removed{‘orange‘, ‘banana‘, ‘pear‘, ‘apple‘}>>> ‘orange‘ in basket # fast membership testingTrue>>> ‘crabgrass‘ in basketFalse>>> # Demonstrate set operations on unique letters from two words...>>> a = set(‘abracadabra‘)>>> b = set(‘alacazam‘)>>> a # unique letters in a{‘a‘, ‘r‘, ‘b‘, ‘c‘, ‘d‘}>>> a - b # letters in a but not in b{‘r‘, ‘d‘, ‘b‘}>>> a | b # letters in either a or b{‘a‘, ‘c‘, ‘r‘, ‘d‘, ‘b‘, ‘m‘, ‘z‘, ‘l‘}>>> a & b # letters in both a and b{‘a‘, ‘c‘}>>> a ^ b # letters in a or b but not both{‘r‘, ‘d‘, ‘b‘, ‘m‘, ‘z‘, ‘l‘}# 集合推导式>>> a = {x for x in ‘abracadabra‘ if x not in ‘abc‘}>>> a{‘r‘, ‘d‘}
5 字典
>>> tel = {‘jack‘: 4098, ‘sape‘: 4139}>>> tel[‘guido‘] = 4127>>> tel{‘sape‘: 4139, ‘guido‘: 4127, ‘jack‘: 4098}>>> tel[‘jack‘]4098>>> del tel[‘sape‘]>>> tel[‘irv‘] = 4127>>> tel{‘guido‘: 4127, ‘irv‘: 4127, ‘jack‘: 4098}>>> list(tel.keys())[‘irv‘, ‘guido‘, ‘jack‘]>>> sorted(tel.keys())[‘guido‘, ‘irv‘, ‘jack‘]>>> ‘guido‘ in telTrue>>> ‘jack‘ not in telFalse
使用dict()构造字典
dict(sape=4139, guido=4127, jack=4908)dict([(‘sape‘, 4139), (‘guido‘, 4127), (‘jack‘, 4098)])
使用简直表达式创建字典
{x: x**2 for x in (2, 4, 6)}
6 循环技巧
字典中的关键字和值的遍历可以用 items() 方法
knights = {‘gallahad‘: ‘the pure‘, ‘robin‘: ‘the brave‘}for k, v in knights.items(): print(k,v)
序列中遍历索引和相应的值可以用 enumerate() 方法
for i, v in enumerate([‘tic‘, ‘tac‘, ‘toe‘]): print(i, v)
同时遍历多个序列时,可使用zip() 方法
questions = [‘name‘, ‘quest‘, ‘favorite color‘]answers = [‘lancelot‘, ‘the holy grail‘, ‘blue‘]for q, a in zip(questions, answers): print(‘What is your {0}? It is {1}.‘.format(q, a))
逆序遍历,使用 reversed() 方法
for i reversed(range(1, 10, 2)): print(i)
7 深入条件控制
>>> string1, string2, string3 = ‘‘, ‘Trondheim‘, ‘Hammer Dance‘>>> non_null = string1 or string2 or string3
8 比较序列和其他类型
序列对象可以和相同的类型进行比较。
(1, 2, 3) < (1, 2, 4)[1, 2, 3] < [1, 2, 4]‘ABC‘ < ‘C‘ < ‘Pascal‘ < ‘Python‘(1, 2, 3, 4) < (1, 2, 4)(1, 2) < (1, 2, -1)(1, 2, 3) == (1.0, 2.0, 3.0)(1, 2, (‘aa‘, ‘ab‘)) < (1, 2, (‘abc‘, ‘a‘), 4)
Python 数据结构
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