数字和字符串

数字类型

整形

整数， 1/2/3/12/2019
整形用来描述什么，身高/年龄/体重

age = 18

height = 180

浮点型

浮点数，小数

salary = 10

print(salary)

复数

z = 1 + 2j

print(z.real,z.imag)

## 1.0 2.0

数字类型方法

print(pow(2,3))  # 幂运算

print(1.2+2.3)  # 3.5

print(0.1+0.2)  # 0.30000000000000004

print(round(0.1+0.44,1))   # 0.5  四舍五入

print(abs(-1))   # 绝对值

print(divmod(16,3))   # 运算结果(商数， 余数

浮点数计算会有误差，小数精准

这就是机器进行二进制计算引入的误差，为了消除这样的误差，进行更加精确的浮点计算，就要是用到decimal模块。

from decimal import *

a = Decimal('0.1')   # Decimal函数传入的浮点数必须加引号，构成字符串形式，传入整数就不用了

b = Decimal('0.2')

print(type(a+b),a+b)  # <class 'decimal.Decimal'> 0.3

print(Decimal(0.1))   #    0.1000000000000000055511151231257827021181583404541015625    Decimal函数传入浮点数并不精确

小数的精准计算：

from decimal import *

getcontext().prec = 4   # 设置有效数字为4

print(Decimal('2.2')/Decimal('1.3'))   # 1.692

from decimal import *

print(Decimal('3.141592653').quantize(Decimal('0.0000')))   # 设定小数位数 这里设置了4位

# 打印结果：3.1416

字符串

name = 'neo'

gender = 'male'

print(name, gender)

三个单引号或三双引号可以换行

poem = '''

When I was a young man, I had liberty, but I did not see it.

I have time, but I did not know it. I have love, but I did not feel it.

Many decades would pass before I understood the meaning of all three.

'''

print(poem)

引号检测机制

print("neo's name is neo")  # 如果字符串中需要有单引号，要用双引号包裹整个字符串

print('''neo's name is "neo"''')

转义

print('neo\'s name is "neo"')   # neo's name is "neo"

print('\tneo')  # \t 4个空格，缩进

换行 \n

print('When I was a young man, I had liberty, but I did not see it.\nI have time, but I did not know it. I have love, but I did not feel it.\nMany decades would pass before I understood the meaning of all three.')

# 打印结果：

When I was a young man, I had liberty, but I did not see it.

I have time, but I did not know it. I have love, but I did not feel it.

Many decades would pass before I understood the meaning of all three.

r 取消转义

print(r'\ta\na')

# 打印结果：\ta\na

\r \r 默认表示将输出的内容返回到第一个指针，这样的话，后面的内容会覆盖前面的内容

字符串运算

print('neo' + '123')   # neo123

print('neo'* 4)        # neoneoneoneo

字符串常用内置方法

s = 'hello world'

res = s.split('o')  # 切割

print(res)

# 打印结果：['hell', ' w', 'rld']

print(s.startswith('h'))  # 以指定字符串开头,就打印True

print(s.endswith('d'))

print(s.center(20,'*'))   # 填充  ****hello world*****

f-string格式化

s1 = 'neo'

s2 = '25'

s3 = 'height'

s4 = 180

print(f'{s1} {s2} {s3} {s4}')  # {} 占位，且数字自动转化为字符串

print('{} {} {} {}'.format(s1,s2,s3,s4))

字符居中/居左/居右

s = 'neo121'

print(f'{s:*^10}')   # **neo121**

print(f'{s:*<10}')   # neo121****

print(f'{s:*>10}')   # ****neo121

time模块

import time

print(time.time())  # 从1970.01.01.00:00开始计算时间

import time

print('-------')

time.sleep(3)  # 睡眠

print('-------')

# cpu级别的时间计算，一般用于程序耗时时间计算

import time

start = time.perf_counter()

for i in range(10):

    print(i)

    time.sleep(0.01)

print(time.perf_counter() - start)

# 打印结果：

0

1

2

3

4

5

6

7

8

9

0.10681829999999998

文本进度条

'''

 0 %[->..........]

10 %[*->.........]

20 %[**->........]

30 %[***->.......]

40 %[****->......]

50 %[*****->.....]

60 %[******->....]

70 %[*******->...]

80 %[********->..]

90 %[*********->.]

100%[**********->]

'''

简单开始

星号在递增，小点在递减，用两个循环

for i in range(10):

    print('*'* i + '.' * (10 - i))

# 打印结果：

..........

*.........

**........

***.......

****......

*****.....

******....

*******...

********..

*********.

for i in range(10):

    print(f'[{"*" * i} -> {"." * (10 - i)}]')

 # 打印结果：

[ -> ..........]

[* -> .........]

[** -> ........]

[*** -> .......]

[**** -> ......]

[***** -> .....]

[****** -> ....]

[******* -> ...]

[******** -> ..]

[********* -> .]

for i in range(10):

    print(f'{i*10: ^3}% [{"*" * i} -> {"." * (10 - i)}]')

# 打印结果：

 0 % [ -> ..........]

10 % [* -> .........]

20 % [** -> ........]

30 % [*** -> .......]

40 % [**** -> ......]

50 % [***** -> .....]

60 % [****** -> ....]

70 % [******* -> ...]

80 % [******** -> ..]

90 % [********* -> .]

继续修改

scale = 11

for i in range(scale):

    print(f'{(i/scale)*scale: ^3.1f}% [{"*" * i} -> {"." * (scale - i)}]')

# 打印结果：

0.0% [ -> ...........]

1.0% [* -> ..........]

2.0% [** -> .........]

3.0% [*** -> ........]

4.0% [**** -> .......]

5.0% [***** -> ......]

6.0% [****** -> .....]

7.0% [******* -> ....]

8.0% [******** -> ...]

9.0% [********* -> ..]

10.0% [********** -> .]

单条显示

scale = 101

for i in range(scale):

    print(f'\r{(i/scale)*scale: ^3.1f}% [{"*" * i} -> {"." * (scale - i)}]', end='')

# 打印结果：

100.0% [**************************************************************************************************** -> .]

文本进度条最终形式

import time

start = time.perf_counter()

scale = 101

for i in range(scale):

    print(f'\r{(i / scale) * scale: ^3.1f}% [{"*" * i} -> {"." * (scale - i)}] {time.perf_counter() - start:.2f}s',

          end='')

    time.sleep(0.1)

巴特西

数字，字符串，time模块，文本进度条

数字和字符串

数字类型

整形

浮点型

复数

数字类型方法

字符串

字符串运算

字符串常用内置方法

time模块

文本进度条

简单开始

继续修改

单条显示

文本进度条最终形式

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