一些python的冷知识，万一用到了呢
finally中的return
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| >>> def t():
... try:
... return "123"
... finally:
... print("123456")
...
>>> t()
123456
'123'
|
- finally中的return语句会覆盖try中的return语句
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| >>> def t():
... try:
... return "123"
... finally:
... return "123456"
...
>>> t()
'123456'
|
+= 与 =+的差异
+=不涉及新对象的创建，而=+语句会产生新对象然后再赋值
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| >>> a = [1, 2]
>>> b = a
>>> a += [3, 4]
>>> a
[1, 2, 3, 4]
>>> b
[1, 2, 3, 4]
|
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| >>> a = [1, 2]
>>> b = a
>>> a = a + [3, 4]
>>> a
[1, 2, 3, 4]
>>> b
[1, 2]
|
便捷查看包搜索路径
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| ❯ python3 -m site
sys.path = [
'/Users/yux1a0',
'/Users/yux1a0/.pyenv/versions/3.6.8/lib/python36.zip',
'/Users/yux1a0/.pyenv/versions/3.6.8/lib/python3.6',
'/Users/yux1a0/.pyenv/versions/3.6.8/lib/python3.6/lib-dynload',
'/Users/yux1a0/.pyenv/versions/3.6.8/lib/python3.6/site-packages',
]
USER_BASE: '/Users/yux1a0/.local' (exists)
USER_SITE: '/Users/yux1a0/.local/lib/python3.6/site-packages' (doesn't exist)
ENABLE_USER_SITE: True
|
脚本出错或结束进入调试模式
python -i <pyfile>
用上下文管理器来处理错误
当类的成员函数都需要统一的错误处理的时候，可以用__exit__来捕获错误
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| class Resource():
def __enter__(self):
print('===connect to resource===')
return self
def __exit__(self, exc_type, exc_val, exc_tb):
print('===close resource connection===')
return True
def operate(self):
1/0
with Resource() as res:
res.operate()
|
exc_type异常类型，exc_val异常值，exc_tb异常栈信息
禁止对象被深拷贝
重写类的__deepcopy__和__copy__方法，使之返回self，就可以禁止对象被深拷贝，本质是deepcopy是调用类的__deepcopy__方法。
集合中某一个满足条件和全部满足条件
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| any(condition(item) for item in items)
all(condition(item) for item in items)
|