python flask框架Bad Request问题

from KNN import *
from flask import Flask,request,render_template

app = Flask(__name__)

@app.route('/',methods=['GET','POST'])
def home():
return render_template('web.html')

@app.route('/training',methods=['GET','POST'])
def training():
pos_path = request.form['positivepath']
neg_path = request.form['negativepath']
Precision,A,B,C,D = algorithm()
return render_template('result.html',precision=Precision,posright=A,poswrong=B,negright=C,negwrong=D)

if name == '__main__':
app.run()

    代码如上，运行后输入localhost:5000能到达web.html，但是提交表单后无法到result.html页面，总是提示Bad Request

The browser (or proxy) sent a request that this server could not understand.

有可能是form表达里面的数据不全，def里面没有拿到想要的值