问仅在Django表单中提交后引发验证错误

EN

class CurrencyConverterForm(forms.Form):
    base_currency = forms.ModelChoiceField(queryset=Currency.objects.all(), required=True)
    counter_currency = forms.ModelChoiceField(queryset=Currency.objects.all(), required=True)
    base_amount = forms.FloatField(required=True)

<form action="" method="get">
    {{ form.non_field_errors }}
    <div class="fieldWrapper">
        {{ form.base_currency.errors }}
        <label for="{{ form.base_currency.id_for_label }}">From Currency</label>
        {{ form.base_currency }}
    </div>
    <div class="fieldWrapper">
        {{ form.counter_currency.errors }}
        <label for="{{ form.counter_currency.id_for_label }}">To Currency</label>
        {{ form.counter_currency }}
    </div>
    <div class="fieldWrapper">
        {{ form.base_amount.errors }}
        <label for="{{ form.base_amount.id_for_label }}">Amount</label>
        {{ form.base_amount }}
    </div>
</form>

def index(request):
    counter_amount = ""
    if request.method == 'GET':
        form = CurrencyConverterForm(request.GET)
        if form.is_valid():
            # Get the input data from the form
            base_currency = form.cleaned_data['base_currency']
            counter_currency = form.cleaned_data['counter_currency']
            base_amount = form.cleaned_data['base_amount']

            # Calculate the counter_amount
            counter_amount = get_conversion_amount(base_currency, counter_currency, datetime.now(), base_amount)
            # Retrieve the counter amount from the dict
            counter_amount = counter_amount['GetConversionAmountResult']
            # Maximize the number of decimals to 4
            if counter_amount.as_tuple().exponent < -4:
                counter_amount = "%.4f" % counter_amount

    else:
        form = CurrencyConverterForm()

    context = {
        'form': form,
        'counter_amount': counter_amount
    }

    return render(request, '../templates/client/index.html', context)