如何修复 django-oscar shipping UnboundLocalError？

Question

我想向 django-oscar 添加运输方式，但我收到 UnboundLocalError 错误，即使我已经完成了文档页面上的所有操作。

Request Method: GET
Request URL:    http://127.0.0.1:8000/checkout/shipping-address/
Django Version: 2.1.7
Exception Type: UnboundLocalError
Exception Value:    
local variable 'methods' referenced before assignment

repository.py

from oscar.apps.shipping import repository
from . import methods

class Repository(repository.Repository):

    def get_available_shipping_methods(self, basket, user=None, shipping_addr=None, request=None, **kwargs):
        methods = (methods.Standard(),)
        if shipping_addr and shipping_addr.country.code == 'GB':
            # Express is only available in the UK
            methods = (methods.Standard(), methods.Express())
        return methods

methods.py

from oscar.apps.shipping import methods
from oscar.core import prices
from decimal import Decimal as D

class Standard(methods.Base):
    code = 'standard'
    name = 'Shipping (Standard)'

    def calculate(self, basket):
        return prices.Price(
            currency=basket.currency,
            excl_tax=D('5.00'), incl_tax=D('5.00'))

class Express(methods.Base):
    code = 'express'
    name = 'Shipping (Express)'

    def calculate(self, basket):
        return prices.Price(
            currency=basket.currency,
            excl_tax=D('4.00'), incl_tax=D('4.00'))

Answer 1

我可以在文档中看到这一点，但他们看起来有一个错误。

使用UnboundLocalError，您实际上是在查看范围问题。一个非常简单的例子是；

x = 10
def foo():
    x += 1
    print x
foo()

当foo 执行时，foo 无法使用 x。所以稍微改变导入以避免这种情况；

from oscar.apps.shipping import repository
from . import methods as shipping_methods

class Repository(repository.Repository):

    def get_available_shipping_methods(self, basket, user=None, shipping_addr=None, request=None, **kwargs):
        methods = (shipping_methods.Standard(),)
        if shipping_addr and shipping_addr.country.code == 'GB':
            # Express is only available in the UK
            methods = (shipping_methods.Standard(), shipping_methods.Express())
        return methods