如何在python中测试变量是否为空
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How to test a variable is null in python
提问by Zephyr Guo
val = ""
del val
if val is None:
print("null")
I ran above code, but got NameError: name 'val' is not defined.
我运行了上面的代码，但得到了NameError: name 'val' is not defined.
How to decide whether a variable is null, and avoid NameError?
如何判断一个变量是否为空，避免NameError？
回答by ?ukasz Rogalski
Testing for name pointing to Noneand name existing are two semantically different operations.
测试名称指向None和名称存在是两个语义不同的操作。
To check if valis None:
要检查是否val为 None：
if val is None:
pass # val exists and is None
To check if name exists:
要检查名称是否存在：
try:
val
except NameError:
pass # val does not exist at all
回答by Ludisposed
try:
if val is None: # The variable
print('It is None')
except NameError:
print ("This variable is not defined")
else:
print ("It is defined and has a value")
回答by cezar
You can do this in a try and catch block:
您可以在 try 和 catch 块中执行此操作：
try:
if val is None:
print("null")
except NameError:
# throw an exception or do something else
