python如何开发小软件,优化seo招聘,云服务器里面做网站播放器,资阳地seo文章目录 1. num,list ,tuple2. list 作为默认值导致共享同一列表3. 防御可变参数4. 结论 1. num,list ,tuple
结论#xff1a;num ,tuple 作为参数#xff0c;自身不会因为函数的原因而改变#xff0c;list 为可变量#xff0c;会因为函数变而变。
测试
def f(a, b):a … 文章目录 1. num,list ,tuple2. list 作为默认值导致共享同一列表3. 防御可变参数4. 结论 1. num,list ,tuple
结论num ,tuple 作为参数自身不会因为函数的原因而改变list 为可变量会因为函数变而变。
测试
def f(a, b):a breturn aif __name__ __main__:x 1y 2result f(x, y)print(**40)print(num 数字作为参数)print(fx {x})print(fy {y})print(fresult{result})print(**40,\n)x1 [1,2]y1 [3,4]result1 f(x1, y1)print(**40)print(list 数字作为参数)print(fx1 {x1})print(fy1 {y1})print(fresult1{result1})print(**40,\n)x2 (1,2)y2 (3,4)result2 f(x2, y2)print(**40)print(tuple 数字作为参数)print(fx2 {x2})print(fy2 {y2})print(fresult2{result2})print(**40)结论
****************************************
num 数字作为参数
x 1
y 2
result3
**************************************** ****************************************
list 数字作为参数
x1 [1, 2, 3, 4]
y1 [3, 4]
result1[1, 2, 3, 4]
**************************************** ****************************************
tuple 数字作为参数
x2 (1, 2)
y2 (3, 4)
result2(1, 2, 3, 4)2. list 作为默认值导致共享同一列表
没有指定初始乘客的HauntedBus实例会共享同一乘客列表
class HauntedBus:备受幽灵乘客折磨的校车# 默认值为list 会导致新实例化的bus2 bus3共享同一列表def __init__(self, passengers[]):# 设置可变类型作为参数默认值self.passengers passengersdef pick(self, name):self.passengers.append(name)def drop(self, name):try:self.passengers.remove(name)except ValueError as e:print(error for , e)if __name__ __main__:bus1 HauntedBus([Alice, Bill])print(fbus1.passengers{bus1.passengers})bus1.pick(Charlie)bus1.drop(Alice)print(fbus1.passengers{bus1.passengers})bus2 HauntedBus()bus2.pick(Carrie)print(fbus2.passengers{bus2.passengers})bus3 HauntedBus()print(fbus3.passengers{bus3.passengers})结果
bus1.passengers[Alice, Bill]
bus1.passengers[Bill, Charlie]
bus2.passengers[Carrie] # bus2 和bus3 没有默认值的情况下共享同一列表
bus3.passengers[Carrie]3. 防御可变参数
缺点 用list 作为形参会改变实参的值
class TwilightBus:让乘客销声匿迹的校车def __init__(self, passengersNone):if passengers is None:self.passengers []else:# 用 passengers 作为参数传入会导致self.passengers# passengers ,basketball_team,# 都为列表[sue, tina, maya, diana, pat] 的别名所以任一改变# 均可改变[sue, tina, maya, diana, pat]的值self.passengers passengersdef pick(self, name):self.passengers.append(name)def drop(self, name):try:self.passengers.remove(name)except ValueError as e:print(Error for , e)if __name__ __main__:basketball_team [sue, tina, maya, diana, pat]bus TwilightBus(basketball_team)print(fbefore : basketball_team{basketball_team})bus.drop(tina)bus.drop(jason)bus.drop(pat)print(fafter : basketball_team{basketball_team})结果
before : basketball_team[sue, tina, maya, diana, pat]
Error for list.remove(x): x not in list
# 列表在经过函数后居然发生变化
after : basketball_team[sue, maya, diana] 方案 应该把参数值的副本赋值给self.passengers, 错误self.passengers passengers 正确self.passengers list(passengers)
class TwilightBus:让乘客销声匿迹的校车def __init__(self, passengersNone):if passengers is None:self.passengers []else:# 用 passengers 作为参数传入会导致self.passengerspassengers ,basketball_team,# 都为列表[sue, tina, maya, diana, pat] 的别名所以任一改变均可改变[sue, tina, maya, diana, pat]的值self.passengers passengersdef pick(self, name):self.passengers.append(name)def drop(self, name):try:self.passengers.remove(name)except ValueError as e:print(Error for , e)class OkBus:def __init__(self, passengersNone):if passengers is None:self.passengers []else:# 创建 passengers 的副本并且赋值给 self.passengers# 重点 list(passengers)!!!!!!!self.passengers list(passengers)def pick(self, name):self.passengers.append(name)def drop(self, name):try:self.passengers.remove(name)except ValueError as e:print(Error for , e)if __name__ __main__:basketball_team [sue, tina, maya, diana, pat]bus TwilightBus(basketball_team)print(**40)print(fbefore : basketball_team{basketball_team})bus.drop(tina)bus.drop(jason)bus.drop(pat)print(fafter : basketball_team{basketball_team})print(**40)basketball_teamok [sue, tina, maya, diana, pat]busok OkBus(basketball_teamok)print(fbefore : basketball_teamok{basketball_teamok})busok.drop(tina)busok.drop(pat)print(fafter : basketball_teamok{basketball_teamok})print(**40)结果
****************************************
# self.passengers passengers 的结果会影响原来的参数列表 basketball_team
before : basketball_team[sue, tina, maya, diana, pat]
Error for list.remove(x): x not in list
after : basketball_team[sue, maya, diana]
****************************************
# self.passengers list(passengers) 的结果不影响 原来的参数列表 basketball_team
before : basketball_teamok[sue, tina, maya, diana, pat]
after : basketball_teamok[sue, tina, maya, diana, pat]
****************************************4. 结论
当函数用参数时尽量用不可变作为形参比如数字元组如果用可变类型作为变量会导致传入的值变化为了解决这个问题判断参数传入的是不是None,并且重新创建新的list
class Bus:def __init__(self,passengersNone):if passengers is None:self.passengers []else:self.passengers list(passengers)
