python学习记录（持续更新）--最最最基础的一部分（条件分支、循环、数组矩阵、元组）

写在前面

本系列教程针对有一定编程经验的伙伴快速入门python基础，一些涉及开发的常识问题，本文并不涉及。

if else 

is_hot= False
is_cold= True

if is_hot :  (可以使用 and or 连接多个条件 not 可取反)
    print("It's a hot day")
elif is_cold:
    print("It's a cold day")
else:
    print("It's a cold day")
print("Enjoy your day")

=>

 It's a cold day

 Enjoy your day

 while

i=1
while i<=5:
    print(i)
    i +=1
else:
    print(2) 跳出后执行一次
=> 1 2 3 4 5 2

for

for item in 'python':
    print(item)
=>

p
y
t
h
o
n

for item in ['Mosh','John','Sarah']:
    print(item)
=>

Mosh
John
Sarah

for item in range(10):
    print(item)
=> 0 1 2 3 4 5 6 7 8 9 

for item in range(5,10):
    print(item) =>5~9

for item in range(5,10,2): 步长
    print(item) => 5,7,9
循环嵌套

for x in range(4):
    for y in range(3):
        print(f'({x},{y})')
=>

(0,0)
(0,1)
(0,2)
(1,0)
(1,1)
(1,2)
(2,0)
(2,1)
(2,2)
(3,0)
(3,1)
(3,2)

 数组

matrix=[
    [1,2,3],
    [4,5,6],
    [7,8,9]
]
print(matrix[0])
print(matrix[1][1])
print(matrix[2][2])
=>
[1, 2, 3]
5
9

for row in matrix:
    for num in row:
        print(num)
=>

1
2
3
4
5
6
7
8
9

添加

numbers=[1,2,3,4,5,6]
numbers.append(10)
print(numbers)
=>
[1, 2, 3, 4, 5, 6, 10]

插入

numbers=[1,2,3,4,5,6]
numbers.insert(1,10)
print(numbers)

=>[1, 10, 2, 3, 4, 5, 6]
删除

numbers=[1,2,3,4,5,6]
numbers.remove(1)
print(numbers)
=>
[2, 3, 4, 5, 6]

numbers=[1,2,3,4,5,6]
numbers.remove(0)
print(numbers)
=>

报错

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

清空

numbers=[1,2,3,4,5,6]
numbers.clear()
print(numbers)

=>[]
末尾删除，出栈

numbers=[1,2,3,4,5,6]
numbers.pop()
print(numbers)
=>[1, 2, 3, 4, 5]

查找

numbers=[1,2,3,4,5,6]
print(numbers.index(5))
=>4

计算个数

numbers=[1,2,3,4,5,6]
print(numbers.count(5))
=>1
排序

numbers=[1,4,3,2,5,6]
numbers.sort()
print(numbers)
=>[1, 2, 3, 4, 5, 6]

反转
numbers=[1,4,3,2,5,6]

numbers.reverse()
print(numbers)
=>[6, 5, 2, 3, 4, 1]

不改变原有数组复制

numbers=[1,4,3,2,5,6] 
numbers2=numbers.copy()

numbers.remove(3)

print(numbers2)
=>

[1,4,3,2,5,6]

会改变原有对象

numbers=[1,4,3,2,5,6]
numbers2=numbers
numbers.remove(3)
print(numbers2)
=>[1, 4, 2, 5, 6]

不能被修改的元组

numbers=(1,2,3)
numbers[0]=23
print(numbers)
=>
报错
TypeError: 'tuple' object does not support item assignment

 压缩特性

coordinates=(1,2,3)
x=coordinates[0]
y=coordinates[1]
z=coordinates[2]
'''等同于'''
x,y,z=coordinates

键值对

customer={
    "name":"Jay chou",
    "age":30
}

print(customer["birthday"])=>报错

print(customer.get("birthday"))=>None

customer["birthday"]="1993/12/22" 添加新键值对
print(customer.get("birthday"))
=>

1993/12/22

print(customer.get("xxx","!"))
=>!