Python Learning notes list, tuples, dictionaries (1)

1, the most basic data structure: sequence

A, any sequence begins with a 0 serial number (also an index);

As follows: The first element is ' H '

>>> a = ' Hello '
>>> A[0]
H

b, sequence of operations:

Shard: A[1:5] #表示从第2个元素到第6个元素, but not including the 6th element

A[-3:-1] #表示从倒数第3个元素到倒数第一个元素, but excluding the first element of the countdown

A[-3:] #表示从倒数第三个元素到最后一个元素, you can take the last element

a[:] #表示a的全部元素

A[1:9:2] #表示从第2个元素到第10个元素, step is 2

As follows:

>>> a = [1,2,3,4,5,6,7,8,9,10]
>>> A[1:5]
[2, 3, 4, 5]
>>> A[-3:-1]
[8, 9]
>>> a[-3:]
[8, 9, 10]
>>> a[:]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> A[1:9:2]
[2, 4, 6, 8]

Addition:

>>> ' python ' + ' + ' selenium '
' Python selenium '

Multiplication:

>>> ' python ' * 3
' Pythonpythonpython '

Membership: In

>>> ' i ' in ' Python '
False
>>> ' py ' in ' python '
True

2. List

The list of individuals feels like a sequence: the main things to keep in mind are list operations and some methods

List function, you can convert the sequence into lists

>>> a = list (' Hello ')
>>> A
[' H ', ' e ', ' l ', ' l ', ' O ']

Del #删除列表里的元素

>>> A
[' H ', ' e ', ' l ', ' l ', ' O ']
>>> del A[0]
>>> A
[' E ', ' l ', ' l ', ' O ']

Append #在列表末尾追加对象

>>> a.append (' H ')

>>> A
[' E ', ' l ', ' l ', ' o ', ' H ']

Count #统计某个元素在列表中出现的次数

>>> a.count (' l ')
2

Extend #在列表末尾一次性追加另一个列表的多个值

>>> b = List (' World ')
>>> a.extend (B[1:3])
>>> A
[' E ', ' l ', ' l ', ' o ', ' H ', ' o ', ' R ']

Index #从列表中找出某个值的第一个匹配项的索引位置

>>> a.index (' O ')
3

Insert #将对象插入列表中

>>> A.insert (4, ' W ')
>>> A
[' E ', ' l ', ' l ', ' o ', ' W ', ' H ', ' o ', ' R ']

Pop #从移除列表中的一个元素 (the last one by default)

>>> A.pop ()
' R '
>>> A
[' E ', ' l ', ' l ', ' o ', ' W ', ' H ', ' O ']
>>> A.pop (4)
W
>>> A
[' E ', ' l ', ' l ', ' o ', ' H ', ' O ']

Remove #移除列表中某个值的第一个匹配项

>>> a.remove (' O ')
>>> A
[' E ', ' l ', ' l ', ' H ', ' O ']

Reverse #将列表中的元素反向存放

>>> A.reverse ()
>>> A
[' O ', ' H ', ' l ', ' l ', ' e ']

Sort #用于在原位置对列表进行排序 (modifies the list) and can be sorted according to the key function

>>> A.sort ()
>>> A
[' H ', ' e ', ' l ', ' l ', ' O ']

>>> b = [' Hello ', ' Hi ', ' See You ']
>>> b.sort (key = len)
>>> b
[' Hi ', ' hello ', ' See You ']

Shard Assignment:

>>> A
[' H ', ' e ', ' l ', ' l ', ' O ']
>>> A[1:3] = [3,4]
>>> A
[' H ', 3, 4, ' l ', ' O ']

3, meta-group

Tuples are immutable sequences, tuples cannot be modified; creating tuples is simple, and the value is a comma.

>>> A = 3,
>>> A
(3,)
>>> A =
>>> A
(1, 2, 3)

The main factors to remember are:

The tuple function converts a sequence to a tuple

>>> a = ' Hello '
>>> Tuple (a)
(' H ', ' e ', ' l ', ' l ', ' o ')

Python Learning notes list, tuples, dictionaries (1)