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urara/2023-09-04-python/+page.md
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---
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title: Python 初学笔记
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created: 2023-09-04
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summary: Note of 《Python As Fast as Possible - Learn Python in ~75 Minutes》
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tags:
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- 笔记
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- Python
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---
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教程：[Python As Fast as Possible - Learn Python in ~75 Minutes](https://www.youtube.com/watch?v=VchuKL44s6E)
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- [GitHub - kyclark/tiny\_python\_projects: Code for Tiny Python Projects (Manning, 2020, ISBN 1617297518). Learning Python through test-driven development of games and puzzles.](https://github.com/kyclark/tiny_python_projects)
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## 交互式
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输入
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```bash
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python3
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```
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看到prompt提示符`>>>` 就进入交互模式了
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- `<Control>`-`P `(previous)
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- `<Control>`-`N` (next).
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- `<Control>`-`D` exits a session
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- 工具：
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- [Project Jupyter | Home](https://jupyter.org)
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- 教程：
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- [practical python](https://dabeaz-course.github.io/practical-python/)
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- [PEP 20 – The Zen of Python | peps.python.org](https://peps.python.org/pep-0020/)
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- 书籍
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- [[流畅的Python]]
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## 数据类型
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- Int
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- Float
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- String
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- Bool
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## Arithmetic Operator
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- will always reture a float number
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- `int(x/y)` => int
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- 幂运算： `x ** y` => `2**3 = 8`
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- 开跟号：`x //y` => `10 // 3 ` => 3 因为返回的是int，会自动取整
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- 求余 `x % y`
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## String Method
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- `.upper()`
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- `.lower()`
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- `.capitalize()`
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- 首字大写
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- `.count()`
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- `'Hello'.count('ll) = 2`
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- mutiply strings
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- `'hello' * 3 = 'hellohellohello`
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- `'hello' + 'yes' = 'helloyes`
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- `.replace()`
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- `.split()` 分割
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- 和JS中[[split]]的区别：
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- 当split里面没有任何参数的时候，JS中会将字符串切割成单个字符
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- 而Python会按照空格分割（By default any whitespace is a separator[^1]）
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## Conditional Operators
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return -> `True` / `False`
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- ==
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- !=
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- `>=`
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- `<=`
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- `>`
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- `<`
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- 可以比较字符串，通过比较ASCI码
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- `.orc('a')` 求得某个字符串的ASCI值
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- 如果有几个字符串的话，逐一比较
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## Chained Conditionals
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- and
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- or
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- not
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- order
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1. nor
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2. and
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3. or
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## If/Else/Elif
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```py
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if x == 'Tim':
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print('You are great')
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elif x == 'joe':
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print('Bye joe!')
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else:
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print('No')
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```
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js
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```js
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if(x === 'tim') {
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console.log('You are great')
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} else if (x === 'joe') {
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console.log('Bye joe!')
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} else {
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console.log('No')
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}
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```
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## List/Tuples
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- List
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- 类似JS中的 [[数组|array]]
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- `.list()`
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- `x = [4, True, 'hi']`
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- `x[index]`
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- `.len()`
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- 返回长度
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- string also works
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- `.append()`
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- 在末尾加值
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- `.extend([])`
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- 扩展数组，在末尾加值
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- `.pop(index)`
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- remove the last element and return it
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- list is mutable
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- deepcopy
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- `y = x[:]
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- tuples
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- TS中的 tuple
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- immutable
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- `y = (1,2,3,5)`
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- nesting
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- `x=[[],(),[]]`
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## for loops
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```py
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for i in range(10)
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print(i)
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x = [1,2,3,5,67]
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for i in range(len(x))
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print(x[i])
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for i,element in enumerate(x):
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print(i,element)
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// 0 1
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// 1 2
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// 2 3
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// 3 5
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// 4 67
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```
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- `.range()`
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- arguments:
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- stop
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- start, stop
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- start, stop, end
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- not includes start and stop
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- `enumerate`
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- enumerate()是Python中的一个内置函数,用于将一个可迭代对象(如列表、元组或字符串)组合为一个索引序列,同时列出数据和数据下标,一般用在for循环当中
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## While
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```bash
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while True:
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print('run')
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i += 1
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```
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## Slice
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切割数组
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```py
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x = [0,1,2,3,4,5,6,7,8]
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slice = x[0,4,2]
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// slice = [0,2]
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```
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- `slice = x[start:stop:step]`
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- `x[:stop]`
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- `x[start:]`
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- `x[start:stop]`
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- step默认为1
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- reverse a list: `x[::-1]`
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## Sets
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unorder unique list
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```py
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x = set()
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s = { 2,3,4,5 } //set
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s2 = { 6 }
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s = { } // dict
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print( 4 in s) => boolean
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print(s.union(s2)) // => {2,3,4,5,6}
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```
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- `.add()`
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- `.remove()`
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- `.union`：合并set
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- `.difference`：比较差异
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- `.intersection`： 交集
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## Dicts
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```py
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x = {'key': 4}
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x['key2'] = 5
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print( 'key' in x) // => True
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//删除
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del x['key']
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```
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- `.value()`
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- 获取所有values
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- `.update()`[^2]
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- update() 方法用于将一个字典的键值对更新到另一个字典中。
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- Update the dictionary with the key/value pairs from other, overwriting existing keys. Return None.
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- update() accepts either another dictionary object or an iterable of key/value pairs (as tuples or other iterables of length two). If keyword arguments are specified, the dictionary is then updated with those key/value pairs: d.update(red=1, blue=2).
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## Comprehensions
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```py
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x = [ x for x in range(5)]
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x =[[0 for x in range(100)] for x in range(5)]
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x = { i for i in range(100) if i % 5 == 0 }
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```
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## Function
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```py
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def func(x,y,z=None):
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print('Run',x,y,z)
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return x * y , x /y
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r1, r2 = func(10,5)
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func()
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```
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## Unpack Operator /* Args and ** Kwargs
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- `*x`
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- 类似于JS中的`...`
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- 用于list
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```py
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def fun(x,y):
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print(x,y)
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pairs = [(1,2),(3,4)]
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for pair in pairs
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fun(*pair)
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```
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- `**x`
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- key word argumens
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- 用于dict
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```py
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def fun(x,y):
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print(x,y)
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for(**{'x':2, 'y': 5})
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// 顺序不一也可以
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```
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## Scope & Globals
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- 函数内有局部作用域
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- 用`globel` 可以将局部变量变成全局变量
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```py
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def func():
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global x
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return x
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```
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## Exceptions
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- 意外事件，相当于JS中的`throw new Error('')`
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- 会打断程序的正常执行流程
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```py
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raise Exception('Bad')
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raise FileExistsError('')
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```
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常见的异常类型有:
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- StopIteration - 迭代器没有更多的值
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- ImportError - 导入模块失败
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- IndexError - 序列中找不到给定的索引
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- KeyError - 映射中找不到给定的键
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- ValueError - 传入无效的参数
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- TypeError - 对类型无效的操作
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- FileNotFoundError - 未找到文件
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- KeyboardInterrupt - 用户中断执行
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## Handling Exceptions
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```py
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try:
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x = 7 /0
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expect Exception as e
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print(e)
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finally:
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print('finally')
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```
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## Lambda
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lambda是Python中的匿名函数。它可以有多个参数,但只能有一个表达式。
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```py
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x = lambda x: x + 5
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```
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## Map and Filter
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- Map: 跟JS的[[map()]] 差不多
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- 返回map object
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```py
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x = [0,1,2,3,4,5,6,7,8]
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mp = map(lambda i : i +2 , x)
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// js : const mp = x.map((i)=> i+1)
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print(list(mp))
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mpf = filter(lambda i : i === 2 , x)
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```
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## F Strings
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- 类似于JS中的 [[template literal]]
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```py
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tim = 89
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x = f'hello {6+8}'
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// js
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// x = `hello ${6+8}`
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```
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## Buildin Functions
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- [[vars()]]
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[^1]: [Python String split() Method](https://www.w3schools.com/python/ref_string_split.asp)
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[^2]: [Built-in Types — Python 3.11.4 documentation](https://docs.python.org/3/library/stdtypes.html?highlight=update#dict.update)
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