分配Django错误之前引用的局部变量

Question

This is my view.py and when i have a form which when i submit with the required fields it gives an appropriate output but when i don't input anything in the form and click submit i get an error saying "local variable 'researcher' referenced before assignment".

Also i want to know how do i keep my form data saved on the destination page

def about_experiment(request,ex_link_name):

    if request.method == 'POST':
        form = AboutHelp(request.POST)
        if form.is_valid():
            researcher = form.cleaned_data['researcher']
            study = form.cleaned_data['study']

    else:
        form = AboutHelp()
    return render(request, 'about_experiment.html', {'researcher': researcher, 'study': study})

my form on the source page is

<form action="{% url 'lazer.views.about_experiment' exp.link_name %}" method="POST" name="form"> 
  {% csrf_token %}
      <label>Researcher Name(s):<input type="text" name="researcher">
    <lable>Study Summary<textarea rows="10" cols="50" placeholder="here you go" maxlength="500" class="form-control" name="study"></textarea>
      <br>
      <input type = "submit" value="Submit" class="btn btn-primary" />
  </form>

My destination page where the form outputs are present

<h4> Name : {{ researcher }} </h4><br>
<h4> Summary : {{ study }} </h4>

Answer 1

researcher and study are not assignment if request method is not POST and form is not valid. You should define this variable before if statement:

def about_experiment(request,ex_link_name):
    researcher = ''
    study = ''
    if request.method == 'POST':
    ...  

Answer 2

in else part of views.py you mentioned researcher variable in render method that is producing this error.

so please add

researcher = None

before if statement

and also add

study = None

that will also create same error

forms.py

from django import forms
from .models import AboutHelp

    class AboutHelpForm(forms.ModelForm):
        class Meta:
            model = AboutHelp
            fields = '__all__'

views.py

def about_experiment(request,ex_link_name):
    researcher = None 
    study = None
    form = AboutHelpForm(request.POST or None)
    if request.method == 'POST':
        if form.is_valid():
            form.save()
    return render(request, 'about_experiment.html', {'researcher': researcher, 'study': study})