python学习笔记4

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python学习笔记4

说明

  1. 分片

Tag = ‘abcdefg’

Tag[2:4]

  1. Python * 5

PythonPythonPythonPythonPython

  1. None 表示什么都没有

s = [None]* 10

s

[None, None, None, None, None, None, None, None, None, None]

  1. In


‘a’ in ‘abcdef’

True

  1. 内建函数:len,min,max

Len函数返回序列中所包含元素的数量

Min和max函数返回序列中的最大值和最小值

  1. List函数(使用于所有的类型的操作)

  2. x

[1, 2, 1]

del x[2]

x

[1, 2]

x[1:]

SyntaxError: invalid syntax

x[1:]

[2]

x

[1, 2]

x[1:1] = [2, 3, 4]

x

[1, 2, 3, 4, 2]

x[2:] = []

x

[1, 2]

x = [[1,2], 1, 1, [2, 1, [1, 2]]]

x

[[1, 2], 1, 1, [2, 1, [1, 2]]]

x.count(1)

2

x.count([1, 2])

1

x.append(3)

x

[[1, 2], 1, 1, [2, 1, [1, 2]], 3]

a= [1, 2, 3]

b = [3, 4, 5]

a.append(b)

a

[1, 2, 3, [3, 4, 5]]

b

[3, 4, 5]

id(a)

43400688

a = [1, 2, 3]

id(a)

43428440

a.append(b)

id(a)

43428440

a

[1, 2, 3, [3, 4, 5]]

a.extend(b)

a

[1, 2, 3, [3, 4, 5], 3, 4, 5]

a+b

[1, 2, 3, [3, 4, 5], 3, 4, 5, 3, 4, 5]

a

[1, 2, 3, [3, 4, 5], 3, 4, 5]

b

[3, 4, 5]

a = a + b

a

[1, 2, 3, [3, 4, 5], 3, 4, 5, 3, 4, 5]

b

[3, 4, 5]

  1. Index

str1 = [‘we’, ‘are’, ‘ok’]

str1

[‘we’, ‘are’, ‘ok’]

str1.index (‘we’)

0

str1.index (‘abc’)

Traceback (most recent call last):

File «», line 1, in

str1.index (‘abc’)

ValueError: list.index(x): x not in list

str1

[‘we’, ‘are’, ‘ok’]

str1.insert(2, ‘not’)

str1

[‘we’, ‘are’, ‘not’, ‘ok’]

  1. Pop移除

x = [1, 2, 3]

x.pop()

3

x

[1, 2]

x.pop(0)

1

x

[2]

注:栈,入栈:push(),append(),出栈pop,pop()

注:队列,入:insert(0, …),出,pop(0)

  1. Remove()

  2. Reverse()反转

x = [1, 2, 3, 4, 5]

x

[1, 2, 3, 4, 5]

x.reverse()

x

[5, 4, 3, 2, 1]

  1. Sort方法用于在原来位置对列表进行排序。注意内存是不变的。

x = [1, 2, 3, 4, 5]

x

[1, 2, 3, 4, 5]

x.reverse()

x

[5, 4, 3, 2, 1]

x= [4, 6, 2, 1, 7, 9]

x

[4, 6, 2, 1, 7, 9]

id(x)

43269736

x.sort()

x

[1, 2, 4, 6, 7, 9]

id(x)

43269736

分配地址y = x[:]

Sorted(‘python’)

x

[4, 6, 2, 1, 7, 9]

x

[4, 6, 2, 1, 7, 9]

y = sorted(x)

x

[4, 6, 2, 1, 7, 9]

y

[1, 2, 4, 6, 7, 9]

  1. Cmp(x, y)

cmp(42, 32)

1

cmp(99, 100)

-1

cmp(1, 1)

0

x

[4, 6, 2, 1, 7, 9]

x.sort(cmp)

x

[1, 2, 4, 6, 7, 9]

x.reverse()

x

[9, 7, 6, 4, 2, 1]

sorted(x).reverse()

x

[9, 7, 6, 4, 2, 1]

y

[1, 2, 4, 6, 7, 9]

sorted(y).reverse()

y

[1, 2, 4, 6, 7, 9]

y

[1, 2, 4, 6, 7, 9]

y.sort(reverse = True)

y

[9, 7, 6, 4, 2, 1]

str1

[‘we’, ‘are’, ‘not’, ‘ok’]

str1.sort(key = len)

str1

[‘we’, ‘ok’, ‘are’, ‘not’]

  1. Tuple函数的功能与list函数基本上是一样的:以一个序列作为参数并把它转换为元组。

tuple(y)

(9, 7, 6, 4, 2, 1)

y

[9, 7, 6, 4, 2, 1]

不返回值的方法:reverse、sort、

参考

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