如何在Pydantic数据类中设置静态预期值并解决参数顺序错误

报错详情 #

在为dataclass字段设置默认值时，出现以下错误：

TypeError: non-default argument 'breakdownAccount' follows default argument

报错代码示例 #

from dataclasses import dataclass
from typing import Literal

@dataclass
class DataInclude:
    currencyAccount: Literal["CNY счет", "AMD счет", "RUB счет", "USD счет", "EUR счет", "GBP счет", "CHF счет"]
    open: bool = True
    accountType: Literal["Текущий счет"]
    currencyCode: Literal[810, 826, 756, 978, 840, 51, 156]
    currency: Literal['CNY', 'AMD', 'RUB', 'USD', 'EUR', 'GBP', 'CHF']

正常运行代码示例 #

from dataclasses import dataclass
from typing import Literal

@dataclass
class DataInclude:
    currencyAccount: Literal["CNY счет", "AMD счет", "RUB счет", "USD счет", "EUR счет", "GBP счет", "CHF счет"]
    open: bool
    accountType: Literal["Текущий счет"]
    currencyCode: Literal[810, 826, 756, 978, 840, 51, 156]
    currency: Literal['CNY', 'AMD', 'RUB', 'USD', 'EUR', 'GBP', 'CHF']

需求：如何为字段设置静态预期默认值，用于API自动化测试？

问题原因 #

Python语法强制要求：所有带默认值的函数参数必须放在无默认值参数的后面。你给open字段设置了默认值=True，但后续的accountType、currencyCode、currency都没有默认值，违反了这个规则，因此触发TypeError。

解决方法 #

根据你的需求，提供两种可行方案：

方案1：调整字段顺序（推荐） #

把带默认值的open字段移到所有无默认值字段的末尾，语法上即可合法设置默认值：

from dataclasses import dataclass
from typing import Literal

@dataclass
class DataInclude:
    currencyAccount: Literal["CNY счет", "AMD счет", "RUB счет", "USD счет", "EUR счет", "GBP счет", "CHF счет"]
    accountType: Literal["Текущий счет"]
    currencyCode: Literal[810, 826, 756, 978, 840, 51, 156]
    currency: Literal['CNY', 'AMD', 'RUB', 'USD', 'EUR', 'GBP', 'CHF']
    open: bool = True  # 带默认值的字段移至末尾

方案2：保留字段顺序，用field和__post_init__处理 #

如果需要保留原有字段顺序，可通过dataclasses.field配合__post_init__方法实现默认值设置，同时保证后续字段仍为必填项：

from dataclasses import dataclass, field
from typing import Literal

@dataclass
class DataInclude:
    currencyAccount: Literal["CNY счет", "AMD счет", "RUB счет", "USD счет", "EUR счет", "GBP счет", "CHF счет"]
    open: bool = field(default=None, init=True)  # 允许传入值，默认设为None
    accountType: Literal["Текущий счет"]
    currencyCode: Literal[810, 826, 756, 978, 840, 51, 156]
    currency: Literal['CNY', 'AMD', 'RUB', 'USD', 'EUR', 'GBP', 'CHF']
    
    def __post_init__(self):
        # 如果未传入open值，设置为预期默认值True
        if self.open is None:
            self.open = True

如果open字段不需要外部传入，仅需固定默认值，可简化为：

from dataclasses import dataclass, field
from typing import Literal

@dataclass
class DataInclude:
    currencyAccount: Literal["CNY счет", "AMD счет", "RUB счет", "USD счет", "EUR счет", "GBP счет", "CHF счет"]
    accountType: Literal["Текущий счет"]
    currencyCode: Literal[810, 826, 756, 978, 840, 51, 156]
    currency: Literal['CNY', 'AMD', 'RUB', 'USD', 'EUR', 'GBP', 'CHF']
    open: bool = field(default=True, init=False)  # 不参与构造函数，固定默认值

内容的提问来源于stack exchange，提问作者Alex