AttributeError: 'NoneType' object has no attribute 'foo'

def load_config(path):
    with open(path) as f:
        data = json.load(f)
    # 忘記 return data

cfg = load_config('config.json')
print(cfg.keys())  
# AttributeError: 'NoneType' object has no attribute 'keys'

class Node:
    def __init__(self, val):
        self.val = val
        self.next = None
    def set_next(self, node):
        self.next = node
        # 返回 None 而非 self
        # return self

n1 = Node(1)
n2 = Node(2)
n1.set_next(n2).set_next(Node(3))
# AttributeError: 'NoneType' object has no attribute 'set_next'

tmp = n1.set_next(n2)
print(tmp)  # None

m = {'a': 1}
print(m.get('b').bit_length())  
# AttributeError: 'NoneType' object has no attribute 'bit_length'

match = re.search(r'(\d+)', 'abc')
print(match.group(1))  
# AttributeError: 'NoneType' object has no attribute 'group'

tag = soup.find('div', id='missing')
print(tag.text)  
# AttributeError: 'NoneType' object has no attribute 'text'

lst = [3, 1, 2]
res = lst.sort()
print(res)        # None
print(res.append) # AttributeError: 'NoneType' object has no attribute 'append'

df2 = df.drop(columns=['nonexistent'])
# pandas drop 默認(rèn)返回新對(duì)象，但如果 inplace=True，就會(huì)返回 None
df2 = df.drop(columns=['col'], inplace=True)
# df2 is None

print(f"obj={obj!r}, type={type(obj)}")

python -m pdb your_script.py

assert config is not None, "配置加載失敗，config 為 None"

from typing import Optional, Dict
def load_config(path: str) -> Dict[str, str]:
    ...

mypy --strict your_module.py

value = obj.get('key')
if value is None:
    # 處理缺失或給默認(rèn)
    value = default_value
else:
    # 安全使用 value.foo()
    do_something(value.foo())

length = data.get('items', []).__len__()

text = getattr(tag, 'text', '')

try:
    result = match.group(1)
except AttributeError:
    result = None

def create_user(data) -> User:
    if not valid(data):
        raise ValueError("Invalid data")
    return User(**data)

import re

def extract_id(s: str):
    # 忘記檢查 search 是否 None
    return re.search(r'id=(\d+)', s).group(1)

print(extract_id("name=foo"))  # 報(bào)錯(cuò)

AttributeError: 'NoneType' object has no attribute 'group'

m = re.search(r'id=(\d+)', s)
print(m, type(m))  # None <class 'NoneType'>

def extract_id(s: str):
    m = re.search(r'id=(\d+)', s)
    if m is None:
        return None  # 或拋出自定義異常
    return m.group(1)

def extract_id(s: str):
    try:
        return re.search(r'id=(\d+)', s).group(1)
    except AttributeError:
        return None

import pytest

@pytest.mark.parametrize("s,expected", [
    ("id=123", "123"),
    ("no id here", None),
])
def test_extract_id(s, expected):
    assert extract_id(s) == expected