python中的错误-“NoneType”类型的对象没有len()

Error in python - object of type 'NoneType' has no len()

提问by Alex

I am not sure what is wrong with my python code:

我不确定我的 python 代码有什么问题：

geneid=request.args.get('geneid')
sql=text('select * from INFO where name=:ident')
genes=engine.execute(sql,ident=geneid).fetchone()
params['objs']=genes
if len(genes)==0:
    flash('NO RESULTS')
return render_template('info.html', **params)

The error message is: TypeError: object of type 'NoneType' has no len()

错误信息是：TypeError: object of type 'NoneType' has no len()

Any suggestion? I would like to show a flash message when there is no result in my query. I tried also (but did not work):

有什么建议吗？当我的查询没有结果时，我想显示一条 Flash 消息。我也试过（但没有用）：

geneid=request.args.get('geneid')
sql=text('select * from INFO where name=:ident')
genes=engine.execute(sql,ident=geneid).fetchone()
params['objs']=genes
if no genes:
    flash('NO RESULTS')
return render_template('info.html', **params)

回答by David Cullen

You are trying to get len(None). What you want is

您正在尝试获取len(None). 你想要的是

if genes is None:
    flash('NO RESULTS')

Note:Python does not have a nokeyword. The closest thing is the notoperator.

注意：Python 没有no关键字。最接近的是not运营商。