确定是否在Python中定义了变量

Question

您如何知道在运行时是否已在代码的特定位置设置了变量？这并不总是很明显，因为（1）可以有条件地设置变量，而（2）可以有条件地删除变量。我正在寻找类似defined()Perl或isset()PHP或defined?Ruby中的东西。

if condition:
    a = 42

# is "a" defined here?

if other_condition:
    del a

# is "a" defined here?

Answer 1

try:
thevariable
except NameError:
print(“well, it WASN’T defined after all!”)
else:
print(“sure, it was defined.”)