我怎样才能得到select>标签选项，由用户使用Flask选择

我有一个用户上传csv文件的表单，该csv文件随后被转换为pandas数据框，列标题自动填充表单中的<select>标记选项。

然后我希望用户选择他们想要的列，我希望使用Flask将该列选择保存在变量中。

但是，我在检索用户随后从这个选择标记中选择的选项时遇到了麻烦。

<form class="form-horizontal" action="" method="post" enctype="multipart/form-data">
  <fieldset>
     <legend>Text Analytics</legend>
     <div class="form-group form-group-lg">
        <label for="inputData" class="col-lg-2 control-label">Choose Data File:</label>
        <div class="col-lg-5">
           <input type="file" class="form-control" required="required" autofocus="autofocus" name="inputData"/>
        </div>
        <div class="col-lg-3">
            <button class="btn btn-primary" type="submit" name="upload">Upload</button>
        </div>
        {% if success %}
        <div class="alert alert-success">
            <a href="#" class="close" data-dismiss="alert" aria-label="close">&times;</a>
            <strong>Success!</strong> {{success}}.
        </div>
        {% endif %}
        {% if error %}
        <div class="alert alert-warning">
            <a href="#" class="close" data-dismiss="alert" aria-label="close">&times;</a>
            <strong>Error:</strong> {{error}}.
        </div>
        {% endif %}
    </div>
     <div class="form-group form-group-lg">
        <label for="colSelect" class="col-lg-2 control-label">Select column for analysis:</label>
        <div class="col-lg-5">
            <select class="form-control" name="colSelect" id="colSelect">
            {% for column in columns %}
                <option id="{{column}}">{{column}}</option>
            {% endfor %}
            </select>
        </div>

My Flask code:

@app.route('/textanalytics', methods = ['GET', 'POST'])
def upload_file():
error = None
success = None
columns = []
col = None
if request.method == "POST":
    if request.files['inputData'] == '':
        error = "No file selected"
    else:
        file = request.files['inputData']
        if file and allowed_file(file.filename):
            filename = secure_filename(file.filename)
            file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
            success = 'File uploaded'
            data = pd.read_csv(os.path.join(app.config['UPLOAD_FOLDER'], filename), header = 0, low_memory = False)
            columns = [i for i in data.columns]
            col = request.form.get('colSelect')
            return render_template('textanalytics.html', success = success, columns = columns, col = col)
        elif file and not allowed_file(file.filename):
            error = 'Incorrect file type, .csv only'
            return render_template('textanalytics.html', error = error)
return render_template('textanalytics.html', error = error, success = success, columns = columns, col = col)

app.add_url_rule('/uploads/<filename>', 'uploaded_file', build_only=True)
app.wsgi_app = SharedDataMiddleware(app.wsgi_app, {'/uploads':  app.config['UPLOAD_FOLDER']})

正如您所看到的，我使用request.form.get('colSelect')来检索选项，但没有任何运气。它只返回None，这是它的初始值。

我有一种感觉，这与我在哪里放置的代码，但我是新的Flask，所以可以做一些帮助。