当我尝试将selectfield中的数据添加到mysql数据库时，出现以下错误：
_mysql\u exceptions.programmingerror\u mysql\u exceptions.programmingerror：在字符串格式化过程中，并非所有参数都已转换
我的代码：

class ContentForm(Form):
category = SelectField("Category: ",choices=[('DataScience','Data Science'), ('ComputerProgramming', 'Computer Programming'),('DigitalMarketing','Digital Marketing'),('Other','Other')], validators=[validators.DataRequired()])
title = StringField("Title: ",validators=[validators.length(min= 5, max = 100), validators.DataRequired()])
content = TextAreaField("Content: ", validators=[validators.length(min = 10), validators.DataRequired()])

@app.route("/addcontent", methods=["GET","POST"])
@login_required
def addcontent():
form = ContentForm(request.form)
if request.method == "POST" and form.validate():
    category = form.category.data
    title = form.title.data
    content = form.content.data
    cursor = mysql.connection.cursor()
    query = "INSERT INTO contents (author, category, title,content) VALUES(%s,%s,%s)"
    cursor.execute(query, (session["username"], category, title, content))
    mysql.connection.commit()
    cursor.close()
    flash("Your content have added successfully. Thanks your contributions.", 'success')
    return redirect(url_for("dashboard"))
return render_template("addcontent.html", form = form)

html格式：

{% from "includes/_formhelpers.html" import render_field %}

<form method="post">

        {{ render_field(form.category, class="form-control", style = "width: 40% !important") }}
        {{ render_field(form.title, class="form-control", style = "width: 40% !important") }}
        {{ render_field(form.content, class="form-control", style = "height: 300px !important") }}

    <button type="submit" class="btn btn-primary btn-lg">Add Content</button>

我怎样才能解决这个问题？