Python 09

一. 课上代码

#删除元素的三种方法
>>> member = ['fish', 'Jack', 'dark', 'David', 'road', 'quiet', 'sun']
>>> member
['fish', 'Jack', 'dark', 'David', 'road', 'quiet', 'sun']
>>> member.remove('David')
>>> member
['fish', 'Jack', 'dark', 'road', 'quiet', 'sun']
>>> member.remove('HsinChi')
Traceback (most recent call last):
  File "<pyshell#5>", line 1, in <module>
    member.remove('HsinChi')
ValueError: list.remove(x): x not in list
#remove()的话必须得知道数组中有哪个具体元素然后再进行删除

>>> del member[1]
>>> member
['fish', 'dark', 'road', 'quiet', 'sun']
>>> del member
>>> member
Traceback (most recent call last):
  File "<pyshell#9>", line 1, in <module>
    member
NameError: name 'member' is not defined
#del 可以将整个数组删除，或者删除特定位置的元素

>>> member = ['fish', 'Jack', 'dark', 'David', 'road', 'quiet', 'sun']
>>> member.pop()
'sun'
>>> member
['fish', 'Jack', 'dark', 'David', 'road', 'quiet']
>>> name = member.pop()
>>> name
'quiet'
>>> member
['fish', 'Jack', 'dark', 'David', 'road']
>>> member.pop(1)
'Jack'
#pop()可以删除特定位置的元素，或者直接删除最后一位的元素

>>> member
['fish', 'dark', 'David', 'road']
>>> member[1:3]
['dark', 'David']
#这个是数组中的切片功能(slice)

>>> member
['fish', 'dark', 'David', 'road']
>>> member[:3]
['fish', 'dark', 'David']
>>> member[1:]
['dark', 'David', 'road']
>>> member[:]
['fish', 'dark', 'David', 'road']
>>> member1 = member[:]
>>> member1
['fish', 'dark', 'David', 'road']
>>> 

>>> list1 = [123]
>>> list2 = [234]
>>> list1 > list2
False
>>> list1 = [123, 456]
>>> list2 = [234, 123]
>>> list1 > list2
False
#此处进行比较，是选第一个元素进行比较，跟后面的元素没有关系

>>> list3 = [123, 456]
>>> (list1 < list2) and (list1 == list3))
SyntaxError: invalid syntax
>>> (list1 < list2) and (list1 == list3)
True
>>> list4 = list1 + list2
>>> list4
[123, 456, 234, 123]
>>> list1 + 'Jack'
Traceback (most recent call last):
  File "<pyshell#12>", line 1, in <module>
    list1 + 'Jack'
TypeError: can only concatenate list (not "str") to list
#此处"+"的用处只能在都是数组的时候才能使用，如果有一方是数组另一方是元素那就不可以
必须用extend()或者append()来对元素进行添加

>>> list3
[123, 456]
>>> list3 * 3
[123, 456, 123, 456, 123, 456]
>>> list3 *= 3
>>> lsit3
Traceback (most recent call last):
  File "<pyshell#16>", line 1, in <module>
    lsit3
NameError: name 'lsit3' is not defined
>>> list3
[123, 456, 123, 456, 123, 456]
>>> list3 *= 5
>>> list3
[123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456]
>>> 123 in list3
True
>>> 'Jack' not in list3
True
>>> 123 not in list3
False
>>> list5 = [123, ['Jack', 'David'], 456]
>>> 'Jack' in list5
False
>>> 'Jack' in list5[1]
True
>>> list5[1][1]
'David'
#此处选取David的方法比较重要

>>> dir(list)
['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']
>>> list3.count(123)
15
>>> list3.index(123)
0
>>> list3.index(123, 3, 7)
4
>>> list3.reverse()
>>> list3
[456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123, 456, 123]
>>> list6 = [4, 23, 6, 7, 3, 8, 43]
>>> list6.sort()
>>> list6
[3, 4, 6, 7, 8, 23, 43]
#sort()是从小到大排序

>>> list6.sort(reverse = True)
>>> list6
[43, 23, 8, 7, 6, 4, 3]
#list.sort(reverse = True)是从大到小排序

>>> list7 = list6
>>> list7
[43, 23, 8, 7, 6, 4, 3]
>>> list8 = list6[:]
>>> list8
[43, 23, 8, 7, 6, 4, 3]
>>> list6.sort()
>>> list7
[3, 4, 6, 7, 8, 23, 43]
>>> list8
[43, 23, 8, 7, 6, 4, 3]
#此处比较重要，需要多加小心
>>> 

二. 测试题

1. list1 = [1, 3, 2, 9, 7, 8]，请问list1[0]和list1[0:1]一样吗？

不一样，list1[0]返回第0个元素的值，list1[0:1]返回一个只含有第0个元素的列表

2. 如果你每次想从列表的末尾取出一个元素，并将这个元素插入到列表的最前边，你会怎么做？

>>> list1 = [1, 3, 2, 9, 7, 8]
>>> list1.insert(0, list1.pop())
>>> list1
[8, 1, 3, 2, 9, 7]

3. 在进行分片的时候，我们知道分片的开始和结束位置需要进行指定，但其实还有另外一个隐藏的设置：步长。在普通分片操作中，步长默认为1，表示逐个遍历元素，也可以人为调整步长，如下所示：

>>> list1 = [1, 3, 2, 9, 7, 8]
>>> list1[0:6:2]
[1, 2, 7]

那么依你推测，关于步长的知识点还有哪些？

>>> list1[::2]
[1, 2, 7]
#简洁分片操作

>>> list1[::0]
Traceback (most recent call last):
  File "<pyshell#6>", line 1, in <module>
    list1[::0]
ValueError: slice step cannot be zero
#步长不能是0，不然就走不动了

>>> list1[::-1]
[8, 7, 9, 2, 3, 1]
>>> list1[::-2]
[8, 9, 3]
#步长可以是负数，改变方向(从尾部开始向左走)

4. list1[-3:-1]可以得到[9, 7]，这是为何？

python的列表支持负数索引