python中的错误-“NoneType"类型的对象没有len() [英] Error in python - object of type 'NoneType' has no len()

问题描述

我不确定我的 python 代码有什么问题:

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

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)

错误信息是:类型错误:NoneType"类型的对象没有 len()

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

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):

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):

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)

推荐答案

您正在尝试获取 len(None).你想要的是

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

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

注意: Python 没有 no 关键字.最接近的是 not 运算符.

Note: Python does not have a no keyword. The closest thing is the not operator.

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