我真的想不出Python需要del关键字的任何原因(而且大多数语言似乎都没有类似的关键字)。例如,与其删除变量,还不如将None赋值给它。当从字典中删除时,可以添加del方法。
在Python中保留del是有原因的吗,还是它是Python前垃圾收集时代的遗迹?
我真的想不出Python需要del关键字的任何原因(而且大多数语言似乎都没有类似的关键字)。例如,与其删除变量,还不如将None赋值给它。当从字典中删除时,可以添加del方法。
在Python中保留del是有原因的吗,还是它是Python前垃圾收集时代的遗迹?
当前回答
I think one of the reasons that del has its own syntax is that replacing it with a function might be hard in certain cases given it operates on the binding or variable and not the value it references. Thus if a function version of del were to be created a context would need to be passed in. del foo would need to become globals().remove('foo') or locals().remove('foo') which gets messy and less readable. Still I say getting rid of del would be good given its seemingly rare use. But removing language features/flaws can be painful. Maybe python 4 will remove it :)
其他回答
有一次我不得不使用:
del serial
serial = None
因为只使用:
serial = None
没有及时释放串口,无法立即再次打开。 从这一课中,我了解到del的真正意思是:“现在就开始!然后等待直到它完成”这在很多情况下都很有用。当然,你可能有一个system.gc.del_this_and_wait_balbalba (obj)。
删除变量与将其设置为None不同
使用del删除变量名可能很少使用,但如果没有关键字,这是无法实现的。如果你可以通过写a=1来创建一个变量名,那么理论上你可以通过删除a来撤销这一点。
在某些情况下,它可以使调试更容易,因为试图访问已删除的变量将引发NameError。
可以删除类实例属性
Python允许你编写如下代码:
class A(object):
def set_a(self, a):
self.a=a
a=A()
a.set_a(3)
if hasattr(a, "a"):
print("Hallo")
如果选择向类实例动态添加属性,当然希望能够通过写入来撤销它
del a.a
除非重新初始化,否则Del将从当前作用域删除变量。将其设置为None将其保留在当前范围内。
a = "python string"
print(a)
del a
print(a)
a = "new python string"
print(a)
输出:
python string
Traceback (most recent call last):
File "testing.py", line 4, in <module>
print(a)
NameError: name 'a' is not defined
I think one of the reasons that del has its own syntax is that replacing it with a function might be hard in certain cases given it operates on the binding or variable and not the value it references. Thus if a function version of del were to be created a context would need to be passed in. del foo would need to become globals().remove('foo') or locals().remove('foo') which gets messy and less readable. Still I say getting rid of del would be good given its seemingly rare use. But removing language features/flaws can be painful. Maybe python 4 will remove it :)
Del经常出现在__init__.py文件中。任何在__init__.py文件中定义的全局变量都将自动“导出”(它将包含在from模块import *中)。避免这种情况的一种方法是定义__all__,但这可能会很混乱,并不是每个人都使用它。
例如,如果你在__init__.py中有这样的代码
import sys
if sys.version_info < (3,):
print("Python 2 not supported")
然后您的模块将导出sys名称。你应该写
import sys
if sys.version_info < (3,):
print("Python 2 not supported")
del sys