python学习笔记4
说明
- 分片
Tag = ‘abcdefg’
Tag[2:4]
- Python * 5
PythonPythonPythonPythonPython
- None 表示什么都没有
s = [None]* 10
s
[None, None, None, None, None, None, None, None, None, None]
- In
‘a’ in ‘abcdef’
True
- 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
List函数（使用于所有的类型的操作）
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]
- 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’]
- 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)
Remove()
Reverse（）反转
x = [1, 2, 3, 4, 5]
x
[1, 2, 3, 4, 5]
x.reverse()
x
[5, 4, 3, 2, 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]
- 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’]
- 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、
