I have a for loop that goes through a list of cities as well as their broad variables (safety, affordability, transit, etc). If there's a match between the city's broad&specific variable and the broad&specific variable the user selects on the page then it assigns a weighted value else the value is 0. I am trying to add the values for each broad variable in the list but I get the error

local variable 'city_variable1_value' referenced before assignment

When I reference city_variable1_value and city_variable2_value as 0 before the first if statement then my

total_city_value = city_variable1_value   city_variable2_value

equals 0 when it should be 0.24 for example. The code is below!

views.py

# list of each variable's broad category
broad_variable_list = ["safety", "affordability", "transit", "language", "attractions"]

# weighting of each variable ranking
weight_variable1 =  0.33
weight_variable2 =  0.24
weight_variable3 =  0.17
weight_variable4 =  0.14
weight_variable5 =  0.12

def get_ranking(request):
    
    # if this is a POST request we need to process the form data
    if request.method == 'POST':
        
        # create a form instance and populate it with data from the request:
        form = RankingForm(request.POST)
        
        # check whether it's valid:
        if form.is_valid():
            
            # process the data in form.cleaned_data as required
            specific_variable1 = form.cleaned_data['specific_variable1']
            specific_variable2 = form.cleaned_data['specific_variable2']

            broad_variable1 = form.cleaned_data['broad_variable1']
            broad_variable2 = form.cleaned_data['broad_variable2']

            # loop through each city in the database
            for cities in City.objects.values_list('city', flat=True):
                print(cities)

                # loop through each broad variable in the list at the top of this page
                for broad_variable in broad_variable_list:

                    # check if the current broad variable is equal to the first broad variable the user chose
                    if broad_variable == broad_variable1:
                        
                        # if the city's specific variable is equal to the specific variable the user chose get the value of it based on it's ranking weight
                        if City.objects.values_list(broad_variable, flat=True).filter(city=cities).first() == specific_variable1:
                            city_variable1_value = 1 * weight_variable1
                            print(city_variable1_value)
                        
                        # else assign a value of 0
                        else:
                            city_variable1_value = 0
                            print(city_variable1_value)

                    # check if the current broad variable is equal to the second broad variable the user chose
                    if broad_variable == broad_variable2:
                        
                        # if the city's specific variable is equal to the specific variable the user chose get the value of it based on it's ranking weight
                        if City.objects.values_list(broad_variable, flat=True).filter(city=cities).first() == specific_variable2:
                            city_variable2_value = 1 * weight_variable2
                            print(city_variable2_value)
                        
                        # else assign a value of 0
                        else:
                            city_variable2_value = 0
                            print(city_variable2_value)
                    
                    total_city_value = city_variable1_value   city_variable2_value
                    print(total_city_value)
                    
        # if a GET (or any other method) we'll create a blank form
    else:
        form = RankingForm()

    return render(request, 'project/home.html', {'form': form})

CodePudding user response：

Your program reached the total_city_value = city_variable1_value city_variable2_value line without ever assigning a value to city_variable1_value. This is possible if the condition broad_variable == broad_variable1 was never true in the for loop which assigns to city_variable1_value.

For a minimal example, if you did this,

def f():
    if False:
        a = 10
    print(a)
f()

you would get the same error UnboundLocalError: local variable 'a' referenced before assignment.

To fix this, just assign a default value to your variables before the if statement which potentially prevents the assignment from happening. For instance,

city_variable1_value = 0
if broad_variable == broad_variable1:
    ...

city_variable2_value = 0
if broad_variable == broad_variable2:
    ...