从CSV实例化weapon类时传入None值引发AssertionError问题排查

问题详情 #

运行Python代码时，通过csv.DictReader读取weapons.csv文件实例化weapon类对象时，触发AssertionError，提示None is not a valid weapontype。注释断言语句后确认，实例化时传入了None作为weapontype参数值。

相关代码 #

#weapon class
import csv

class weapon:

discount = 0.8 # 20% 

purchase_log = []

def __init__(self, name: str, weapontype : str, range : str, material : str, price : float, quantity=0):

    assert weapontype in ["bladed", "blunt", "polearm", "ranged"], f"{weapontype} is not a valid weapontype"
    assert range in ["close range", "medium range", "long range"], f"{range} is not a valid range"
    assert material in ["iron", "steel", "wood"], f"{material} is not a valid material type"
    
    self.name = name
    self.weapontype = weapontype
    self.range = range
    self.material = material
    self.price = price
    self.quantity = quantity
    
    weapon.purchase_log.append(self)

@classmethod
def instantiate_weapon_orders(cls):
    
    with open('weapons.csv', 'r') as f:
        
        item_reader = csv.DictReader(f) 
        items = list(item_reader) 
    
    for item in items:
        
        weapon(
            name=item.get('name'),
            weapontype=item.get('weapontype'),
            range=item.get('range'),
            material=item.get('material'),
            price=item.get('price'),
            quantity=item.get('quantity')
            )

def __repr__(self):
    
    return f"Weapon({self.name}, {self.weapontype}, {self.range}, {self.material}, {self.price}, {self.quantity})"
        
weapon.instantiate_weapon_orders()

print(weapon.purchase_log)

CSV文件内容 #

name, weapontype, range, material, price, quantity
"Dagger", "bladed", "close range", "steel", 50, 4
"Mace", "blunt", "close range", "steel", 200, 5
"Longsword", "bladed", "medium range", "steel", 350, 3
"Halberd", "polearm", "long range", "steel", 500, 1
"Crossbow", "ranged", "long range", "wood", 500, 3

错误信息 #

File "c:\PythonProjects\expa\random\gw.py", line 58, in <module>
    weapon.instantiate_weapon_orders()
  File "c:\PythonProjects\expa\random\gw.py", line 45, in instantiate_weapon_orders
    weapon(
  File "c:\PythonProjects\expa\random\gw.py", line 12, in __init__
    assert weapontype in ["bladed", "blunt", "polearm", "ranged"], f"{weapontype} is not a valid weapontype"
AssertionError: None is not a valid weapontype

错误原因 #

CSV文件的表头中，每个字段名后带有空格（比如name, weapontype里逗号后有空格），导致csv.DictReader解析后生成的字典键是带前导空格的（比如键为" weapontype"而非"weapontype"）。当用item.get('weapontype')查找时，找不到对应键，返回默认值None，触发断言错误。

解决方案 #

有两种可行的修复方式：

方式一：修改CSV文件 #

直接修改CSV表头，去掉逗号后的所有空格，修改后的表头应为：

name,weapontype,range,material,price,quantity

方式二：在代码中处理键 #

如果不想修改CSV文件，可以在读取数据时对字典的键进行处理，去除前后空格，同时注意将CSV读取的字符串类型字段转换为对应数值类型：

@classmethod
def instantiate_weapon_orders(cls):
    
    with open('weapons.csv', 'r') as f:
        
        item_reader = csv.DictReader(f) 
        # 处理每个字典的键和值，去除前后空格
        items = [{k.strip(): v.strip() for k, v in item.items()} for item in item_reader]
    
    for item in items:
        
        weapon(
            name=item.get('name'),
            weapontype=item.get('weapontype'),
            range=item.get('range'),
            material=item.get('material'),
            price=float(item.get('price')),
            quantity=int(item.get('quantity'))
            )

内容的提问来源于stack exchange，提问作者user19803102