<pre><code>val = ""
del val
if val is None:
print("null")
</code></pre>
<p>我运行了上面的代码,但是得到了<code>NameError: name 'val' is not defined</code>。</p>
<p>如何判断变量是否为空,避免命名错误?</p>
<pre><code>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")
</code></pre>