Python的类成员变量默认初始值的坑及解决

# Define class
class Variant():
    # use
    def __init__(self, price = 500, description = 'default description', values = ['', '', '']):
        self.price = price
        self.description = description
        self.values = values
    
    def __str__(self):
        return 'price: {}, description: {}, values: {}'.format(self.price, self.description, self.values)

variant_list = []
# Create instance with same name iteratively
for i in range(3):
    current_variant = Variant()
    if i == 1:
        current_variant.values[2] = 'hello'
    current_variant.price = i
    current_variant.description = 'description of variant: {}'.format(i)
    variant_list.append(current_variant)
    
# Test results
for variant in variant_list:
    print(str(variant))

def fun(a, b=[]):
    b += [a]
    print(b)

fun(1)
fun(2,[])
fun(3)

def function(a, b=None):
    b = b if b else []  # 明确每次重新定义b
    b += [a]
    print(b)

function(1)
function(2, [])
function(3)