# Section 64~70
## 65 Code Metrics
Cyclomatic complexity
- Radon 氡
- cc
[Introduction to Code Metrics](https://radon.readthedocs.io/en/latest/intro.html)

    - raw
    選能理解的metrics
- Xenon 氙
- [mccabe](https://pypi.org/project/mccabe/)
## 66. Typing 1 (type hints, autocompletion, static vs dynamic type checking)
- https://realpython.com/videos/dynamic-vs-static/
Python 是動態型別（Dynamic Typing）語言，變數的型別是在程式執行時才決定。

x = 10 # int
x = "Hello" # str
x = [1, 2] # list

- Duck Typing 概念是注重物件擁有的方法或屬性，而不是它的類型或所屬類別。
https://zhuanlan.zhihu.com/p/489207162
## 67. Typing 2 (Mypy and basic typing)
- PEP 484 提出型別提示（Type Hints），提高可讀性/可維護性，並允許開發者顯式標註變數的型別

x: int = 10
name: str = "Hi"

- mypy
    - code

# example.py

def add(a: int, b: int) -> int:
return a + b

result = add(5, 10)

result2 = add("5", 10)

    - output

example.py:9: error: Argument 1 to "add" has incompatible type "str"; expected "int"

## 68. Typing 3 (Simple and Complex Types)
- [mypy doc](https://mypy.readthedocs.io/en/stable/) 
- [typing](https://docs.python.org/3/library/typing.html)
## 69. Typing 4 (Union and Optional)
- Union
    - 值可以是多種不同類型

from typing import Union

def add(a: Union[int, float], b: Union[int, float]) -> Union[int, float]:
return a + b

print(add(2, 3)) # 5
print(add(2.5, 3.5)) # 6.0

- Optional
    - 值可以是某種類型，也可是None。```Optional[X]``` 等同 ```Union[X, None]```

from typing import Optional

def greet(name: Optional[str]) -> str:
if name is None:
return "Hello, Stranger!"
return f"Hello, {name}!"

print(greet("ABC")) # Hello, ABC!
print(greet(None)) # Hello, Stranger!

## 70. Typing 5 (TypedDict, dataclasses, NamedTuple, self-referential types)
- TypedDict
    - 具有固定key，對應型別的dictionary

from typing import TypedDict

class Person(TypedDict):
name: str
age: int
email: str

# 使用範例
person: Person = {
"name": "ABC",
"age": 30,
"email": "[e-mail]"
}

print(person["name"])

    - 固定的鍵

Dict[str, Union[str, int]]

- dataclasses
    - use dataclasses

from dataclasses import dataclass

@dataclass
class Person:
name: str
age: int
email: str

# 使用範例
person = Person(name="ABC", age=30, email="[e-mail]")

    - without dataclasses

class Person:
def __init__(self, name: str, age: int, email: str):
self.name = name
self.age = age
self.email = email

def __repr__(self):
return f"Person(name='{self.name}', age={self.age}, email='{self.email}')"

person = Person(name="ABC", age=30, email="[e-mail]")

- ```from __future__ import annotations``` 延遲解析
    -  Python 3.9 
        -  Error

from typing import Optional

class A:
def __init__(self, other: Optional[A] = None):
self.other = other

NameError: name 'A' is not defined

        - Use ```from __future__ import annotations```

from __future__ import annotations
from typing import Optional

class A:
def __init__(self, other: Optional[A] = None):
self.other = other

    - Python 3.10 + 
        - [PEP 604](https://docs.python.org/3/whatsnew/3.10.html)

class A:
def __init__(self, other: A | None = None):
self.other = other