Python is an object-oriented language, so the exceptions thrown by the program are also of the same class
. Access unknown object property ValueError The parameter type passed to the function is incorrect, such as passing a string shape to the int() function UnboundLocalError Unbound local error
(2) The following are the problems and solutions I have encountered recently:
①python local/local variable reference assignment problem
Refreshing the web server while working on a project prompts an error: UnboundLocalError: local variable 'user_sub' referenced before assignment
So try to test out a solution
Server prompt (UnboundLocalError: reference to local variable 'user_sub' before assignment)
def cart(request):
user_sub = 0 //Add this sentence when repairing, and assign a value to user_sub to solve it
cartModel = CartModel.objects.all()
total = 0
for commodity in CartModel.objects.all():
total += commodity.count
total = int(total)
user_sub = CartModel.sub_list(commodity, CartModel.objects.all())
commodity.save()
return render(request, 'cart/cart.html', {'cartModel':cartModel, 'total':total, 'user_sub':user_sub})
At first, I added a global user_sub global variable attribute to user_sub, and then the server prompted user_sub is not defined.
Correctly corrected, I think the for loop belongs to a scope, there is an assignment to user_sub. But it cannot be seen from the outside, which is equivalent to referencing the local variable user_sub before assigning the variable user_sub.
②The server reports an error: AttributeError: 'int' object has no attribute 'save' (attribute error: 'int' object has no attribute' save)
According to the server prompt, I found the error line, this line function calculates the price of the product
total += commodity.count total = int(total) count = commodity.count price = commodity.price commodity.money = count * price commodity.save()
After the modification, it was found that the line was not aligned, and the last two lines were indented and aligned.
**Note**: Here is a reminder that python precedence is related to line alignment, and many small problems are also caused by line alignment
③ValueError: invalid literal for int() with base 10: 'Coca-Cola'
(meaning value error: invalid literal value for int() is 10: 'Coca-Cola')
The parameter type passed to the function is incorrect, such as passing a string shape to the int() function, which is the mistake I made
product_id = request.POST['id'] //this is the id sent by my POST request //Now I check the output and find that the id passed is Chinese characters, so I can correct the POST sending data (Note here: id cannot be Chinese characters)
④The problem of referencing JS files
Server error: Uncaught ReferenceError: connect is not defined
This is a reference file problem, and the header can be imported, and the template page type
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.0/jquery.min.js"></script> //because $ is defined in jquery.js
⑤ HTML template page calculation error
item.count is the number of items, the preferential condition is buy three get one free
The price calculation formula in the model is
def act_price(self):
self.tot_money = (self.count - int(self.count / 3)) * self.price
self.save()
The gift amount can be calculated on the HTML page
At first I wrote
<span class='gift_num'>{% widthratio item.count 3 %}</span>
The server reports an error after running: (TemplateSyntaxError("widthratio takes at least three arguments")
It means TemplateSyntaxError ("widthratio requires at least three parameters"), so add parameter 1
The correct spelling is
<span class='gift_num'>{% widthratio item.count 3 1 %}</span> //widthratio宽度比
(3) Supplement: Django template algorithm
<addition>: {{ value|add:10}}
value=5, return 15
<减法>：{{value|add:-10}}
value=5，则返回-5，减法就是加一个负数
<乘法>：{% widthratio 5 1 100 %}
（注意：该算法会四舍五入，不适合小数点运算）
表示5/1 *100，返回500，widthratio需要三个参数，它会使用 参数1/参数2*参数3，所以要进行乘法的话，就将参数2设为1即可
<除法>:{% widthratio 5 100 1 %}
表示：5/100*1，返回0.05，只需要将第三个参数设置为1即可
（注意：参数个数不符合时，服务器会报错参数个数异常）)