賦值前引用的 django 局部變量 't'

Question

我看到這是一個常見錯誤，我確實查看了其他帖子，但他們沒有幫助我。

我收到錯誤

Exception Value: local variable 't' referenced before assignment

但是我的 t 變量在我的 if 驗證中被聲明為高於它所說的 3 行。 Scope 應該適合我的回歸。

function 有問題：

def create(response):
        #response.user
        if response.method == "POST":
                form = CreateNewTrade(response.POST)
                if form.is_valid():
                        n = form.cleaned_data["name"]
                        t = AssetList(name=n)
                        t.save()
                        response.user.assetlist.add(t)

                return HttpResponseRedirect("/userdash/%i" %t.id) #we fail at this t variable

完整代碼：

$ cat userdash/views.py

from django.shortcuts import render
from django.http import HttpResponse, HttpResponseRedirect
from .models import AssetList, Items
from .forms import CreateNewTrade

# Create your views here.


#def index(response):
#       return HttpResponse("<h1>Hello Dark World!</h1>")

def userdash(response, id):
        ls = AssetList.objects.get(id=id)
        if response.method == "POST":
                print(response.POST)
                if response.POST.get("save"):
                        for item in ls.items_set.all():
                                if response.POST.get("c" + str(item.id)) == "clicked":
                                        item.sell_asset = True
                                else:
                                        item.sell_asset = False

                                item.save()

                elif response.POST.get("newItem"):
                        txt = response.POST.get("new")
                        if len(txt) > 2: #this validation is retarded and needs to be fixed
                                ls.items_set.create(user_asset=txt, sell_asset=False)
                        else:
                                print("invalid")


        #items = ls.items_set.get(id=1)
        #return HttpResponse("<h1>User Dashboard!</h1><h2>%s</h2><br></br><p>%s</p>" %(ls.name, str(items.user_asset)))
        return render(response, "userdash/list.html", {"ls":ls})

def home(response):
        #pass
        return render(response, "userdash/home.html", {})

def create(response):
        #response.user
        if response.method == "POST":
                form = CreateNewTrade(response.POST)
                if form.is_valid():
                        n = form.cleaned_data["name"]
                        t = AssetList(name=n)
                        t.save()
                        response.user.assetlist.add(t)

                return HttpResponseRedirect("/userdash/%i" %t.id)
        else:
                form = CreateNewTrade()
        return render(response, "userdash/create.html", {"form":form})

def view(response):
        return render(response, "userdash/view.html", {})

$ cat userdash/models.py

from django.db import models
from django.contrib.auth.models import User
# Create your models here.

class AssetList(models.Model):
        user = models.ForeignKey(User, on_delete=models.CASCADE, related_name="assetlist", null=True)
        name = models.CharField(max_length=200)

        def __str__(self):
                return self.name

class Items(models.Model):
        assetlist = models.ForeignKey(AssetList, on_delete=models.CASCADE)
        user_asset = models.CharField(max_length=300)
        sell_asset = models.BooleanField()

        def __str__(self):
                return self.user_asset

$ cat userdash/templates/userdash/view.html

{% extends 'userdash/base.html' %}

{% block title %} View page {% endblock %}
{% load crispy_forms_tags %}


{% block content %}
        {% for td in user.assetlist.all %}
                        <p><a href="/{{td.id}}">{{td.name}}</a></p>
        {% endfor %}

{% endblock %}

錯誤：

UnboundLocalError at /create/

local variable 't' referenced before assignment

Request Method:     POST
Request URL:    http://192.168.42.14:8081/create/
Django Version:     3.0.5
Exception Type:     UnboundLocalError
Exception Value:    

local variable 't' referenced before assignment

Exception Location:     ./userdash/views.py in create, line 51
Python Executable:  /usr/local/bin/uwsgi
Python Version:     3.7.3
Python Path:    

['.',
 '',
 '/home/piggy/Env/lib/python37.zip',
 '/home/piggy/Env/lib/python3.7',
 '/home/piggy/Env/lib/python3.7/lib-dynload',
 '/usr/lib/python3.7',
 '/home/piggy/Env/lib/python3.7/site-packages']

如何分配我的 t 變量，以便我的 return 語句接受它？

Answer 1

這是因為您的表格無效。 因此，它將直接 go 到返回的HttpResponseRedirect部分，其中t未定義。

def create(response):
        if response.method == "POST":
                form = CreateNewTrade(response.POST)

                # Because form.is_valid() failed, t will be undefined
                if form.is_valid():
                        n = form.cleaned_data["name"]

                        # Here only, you have assigned value of t
                        t = AssetList(name=n)
                        t.save()
                        response.user.assetlist.add(t)

                # Returns directly to this line, if you see indentation, t is not defined 
                return HttpResponseRedirect("/userdash/%i" %t.id)

請參閱上面的評論以了解發生了什么。 因此，可能的錯誤減少器可能是：

# Define t globaly inside create() method
def create(response):
        t = None
        if response.method == "POST":

現在，您已經在 function 中全局定義了t=None ，它不會顯示之前顯示的錯誤。 但是，仍然會有問題，因為t是None 。 所以，它不會有任何屬性id 。 因此，將顯示has no attribute DoesNotExist 。 因此，您必須考慮如果表單無效該怎么辦，重定向到哪里。

或者，如果表單無效，您可以使用 else 語句處理問題。 喜歡：

def create(response):
        if response.method == "POST":
                form = CreateNewTrade(response.POST)

                # Because form.is_valid() failed, t will be undefined
                if form.is_valid():
                        n = form.cleaned_data["name"]

                        # Here only, you have assigned value of t
                        t = AssetList(name=n)
                        t.save()
                        response.user.assetlist.add(t)

                        return HttpResponseRedirect("/userdash/%i" %t.id)

        # When if statements doesnot apply, always come to this line unless it goes inside form.is_valid()
        return HttpResponseRedirect("/userdash/")   # redirect to the page whose arguments doesnot depend upon the form subbmission

現在，我希望您了解問題所在。

Answer 2

您create的 function 應該返回什么表格無效？

如果表單無效，您將引用不存在的t變量的值。 您應該在 if 之外創建此變量（如果您想返回默認值），或者如果表單無效，則向用戶返回錯誤。

Answer 3

在這里，您在 if 語句中定義了 t 但它不能保證始終運行，因此有可能沒有 t 變量（如果 if 語句失敗）。 t 也是 if 語句的局部變量，不能在它之外使用（除非它在 if 語句下）。

`def create(response):
        #response.user
        if response.method == "POST":
                form = CreateNewTrade(response.POST)
                if form.is_valid():
                        n = form.cleaned_data["name"]
                        t = AssetList(name=n) #t created here
                        t.save()
                        response.user.assetlist.add(t)

                return HttpResponseRedirect("/userdash/%i" %t.id) #here we are outside the if statement`

建議修復

`def create(response):
        #response.user
        if response.method == "POST":
                form = CreateNewTrade(response.POST)
                if form.is_valid():
                        n = form.cleaned_data["name"]
                        t = AssetList(name=n) #t created here
                        t.save()
                        response.user.assetlist.add(t)
                        return HttpResponseRedirect("/userdash/%i" %t.id) #here t is defined but your code will not handle if if response.method == "POST" but form is not valid.`

如果你願意，嘗試處理 if 語句失敗（對不起我的標簽系統，所以不會接受它作為代碼，不知道為什么）

`def create(response):
    #response.user
    if response.method == "POST":
        form = CreateNewTrade(response.POST)
        if form.is_valid():
            n = form.cleaned_data["name"]
            t = AssetList(name=n) #t created here
            t.save()
            response.user.assetlist.add(t)
            return HttpResponseRedirect("/userdash/%i" %t.id) 
        else:
            #handle if inner if fails`