使用dataclass读取将属性设置为datetime对象的文本文件

Question

我试图强迫自己养成使用数据类的习惯。我正在读取一个包含数据行的文本文件，其中两列包含日期。当我将文件读入类时，为什么日期没有转换为datetime对象

import datetime
from dataclasses import dataclass

@dataclass
class AC07:
    NAME: str
    MADE_FROM_DATE: datetime.datetime
    MADE_UPTO_DATE: datetime.datetime
    
counter = 0
deck = []
with open(filename, encoding="latin-1") as file:
    for line in file:
        args = line.strip().split("|")[1:]  # not interested in first column
        data = AC07(*args)
        deck.append(data)
        counter += 1
        if counter == 10:
            break
        
print (type(deck[0].MADE_FROM_DATE))
<class 'str'>
# Expected behavior <class datetime.datetime> 

Answer 1

现在我更好地理解了@vasco ludovico发布的答案，为了解决我的问题，我使用了下面的代码：

with open(filename, encoding="latin-1") as file:
    for line in file:
        args = line.strip().split("|")[1:]  # not interested in first column
        data = AC07(*args)
        data.MADE_FROM_DATE = datetime.datetime.strptime(data.MADE_FROM_DATE, "%d/%m/%Y")
        deck.append(data)
        counter += 1
        if counter == 10:
            break

Answer 2

请有人纠正我，如果我错了，但我相信数据类不强制类型。在您的示例中，datetime.datetime（几乎）只是一个注释，除了两个实现细节之外。检查documentation。具体来说,

The dataclass() decorator examines the class to find fields. A field is defined as class variable that has a type annotation. With two exceptions described below, nothing in dataclass() examines the type specified in the variable annotation.

这两个例外与强制数据类型无关：

Class variables One of two places where dataclass() actually inspects the type of a field is to determine if a field is a class variable as defined in PEP 526. It does this by checking if the type of the field is typing.ClassVar. If a field is a ClassVar, it is excluded from consideration as a field and is ignored by the dataclass mechanisms. Such ClassVar pseudo-fields are not returned by the module-level fields() function.

Init-only variables The other place where dataclass() inspects a type annotation is to determine if a field is an init-only variable. It does this by seeing if the type of a field is of type dataclasses.InitVar. If a field is an InitVar, it is considered a pseudo-field called an init-only field. As it is not a true field, it is not returned by the module-level fields() function. Init-only fields are added as parameters to the generated __init__() method, and are passed to the optional __post_init__() method. They are not otherwise used by dataclasses.