型別註記

Python 物件導向程式設計進階

Jake Roach

Data Engineer

沒有型別註記的程式碼

class Student:
    def __init__(self, name, student_id, tuition_balance):
        self.name = name
        self.student_id = student_id
        self.tuition_balance = tuition_balance

# Trying to create a class can be tricky
walker = Student("Sarah Walker", 319921, 15000)

student_id 應該是整數嗎？
tuition_balance 該用 float 還是整數？或是字串？
建立 walker 之後，之後在程式裡要怎麼記住它的型別？

型別註記

可選用的工具，讓你在程式碼中加入物件的資訊。

更易讀、較好除錯
展現企業級 Python 技能的最佳方式之一
直譯器不會強制執行
內建型別關鍵字、typing 函式庫、自訂類別

# Add type hinting when creating a 
# variable
gpa: float = 3.92

# Add type hinting to a function/method 
# definition
def check_grades(year: str) -> List[int]:
    ...

# Can even use custom classes
students: Dict[str, Student] = {...}

使用內建型別關鍵字做型別註記

# Type hinting for declarative logic
name: str = "Frost"  # Before: name = "Frost"
student_id: int = 91031367
tuition_balance: float = 17452.78

# Type hinting for function/method definitions
def get_schedule(semester: str) -> dict:
    ...

使用語法 variable: type
宣告式、做為函式／方法簽章
用 def .... () -> type: 指定回傳型別

typing 函式庫

typing 是用來提供更多型別註記工具的函式庫。

List、Dict、Tuple
可標註最外層物件與其元素

from typing import List, Dict

student_names: List[str] = ["Morgan", "Chuck", "Anna"]
student_gpas: Dict[str, float] = {
    "Casey": 3.71,
    "Sarah": 4.0
}

Any、Set、Iterator、Callable

以自訂類別進行型別註記

class Student:
    def __init__(self, name: str, student_id: int, tuition_balance: float) -> None:
        self.name: str = name
        self.student_id: int = student_id
        self.tuition_balance: float = tuition_balance

    def get_course(self, course_id: str) -> Course:
        ...
        return course

# Use Student and Course to type hint
walker: Student = Student("Sarah Walker", 319921, 15000)
data_science: Course = walker.get_course("TDM-20100")

檢查物件型別

# walker: Student = Student("Sarah Walker", 319921, 15000)
print(type(walker))

<class '__main__.Student'>

# data_science: Course = walker.get_course("TDM-20100")
print(type(data_science))

<class '__main__.Course'>

一起來練習吧！

Python 物件導向程式設計進階