一、函数定义
二、作用：提高代码的可重用性和可维护性（代码层次结构更清晰）。
三、函数返回值：
四、实例
# 定义根据月份，判断季节的方法．
def get_season(month): if month < 1 or month > 12: return "输入有误"
if month <= 3: return "春天"
if month <= 6: return "夏天"
if month <= 9: return "秋天"
return "冬天"
print(get_season(5)) print(get_season(15)) # 练习：定义检查列表是否具有相同元素的方法
def is_repeating(list_target): for r in range(len(list_target) - 1): for c in range(r + 1, len(list_target)): if list_target[r] == list_target[c]: return True # 退出方法(可以退出两层循环)
return False re01 = is_repeating([3,44,5]) re01 = is_repeating([3,44,5,44]) print(re01) #练习：定义在控制台中显示直角三角形的函数
def print_triangle(height,char): """ 打印三角型 :param height: 三角形高度 :param char: 组成三角型的字符 :return: """
for r in range(height): for c in range(r+1): print(char, end="") print() print_triangle(8,"*") print_triangle(5,"#") print_triangle(4,"?") # 练习：定义在控制台中显示矩形的函数
def print_rect(r_count,c_count,char): for r in range(r_count):# 0 1 2
for c in range(c_count):#01234 01234 01234
print(char,end = "") # 在一行输出
print() # 换行
print_rect(2,3,"*") print_rect(5,2,"#") # 参数:变量 # 函数调用者 告诉 函数定义者的信息
# 1. 参照下列代码，定义判断是否是奇数的方法． # number = int(input("请输入整数:")) # if number % 2 == 1: # print("奇数") # else: # print("偶数")
def is_uneven(number): # 方法１：传统方法
# if number % 2 == 1:
# return True
# else:
# return False
# 方法２：条件表达式
# return True if number % 2 == 1 else False
# 方法３：bool表达式
return number % 2 == 1 re = is_uneven(6) print(re)
# 2.参照下列代码，定义根据月份返回天数的方法． # 要求：考虑２月，如果是闰年返回２９天，否则返回２８天． # month = int(input("请输入月份:")) # if month < 1 or month > 12: # print("输入有误") # elif month == 2: # print("28天") # elif month == 4 or month == 6 or month == 9 or month == 11: # print("30天") # else: # print("31天")
# 向外返回的结果return，其类型应该统一． # 方法１：传统方法： # def get_day_by_month(year,month): # if month < 1 or month > 12: # return 0 # elif month == 2: # if year % 4 == 0 and year % 100 != 0 or year % 400 ==0: # return 29 # else: # return 28 # elif month == 4 or month == 6 or month == 9 or month == 11: # return 30 # else: # return 31
# 方法２：定义函数嵌套法+条件表达式精简代码
def is_leap_year(year): return year % 4 == 0 and year % 100 != 0 or year % 400 == 0 def get_day_by_month(year, month): if month < 1 or month > 12: return 0 if month == 2: return 29 if is_leap_year(year) else 28
if month in (4, 6, 9, 11): return 30
return 31 day = get_day_by_month(2019,13) print(day)
# 3.参照下列代码，定义获取最小值方法． # min = list01[0] # for i in range(1, len(list01)): # # 发现更大的，则替换假设的． # if min > list01[i]: # min = list01[i] # print(min)
def get_min(list_target): min = list_target[0] for i in range(1, len(list_target)): if min > list_target[i]: min = list_target[i] return min min = get_min([2, 3, 45, 1, 9, 3]) print(min)
# 4. 定义函数，判断字符串中存在的中文字符数量． # 中文编码范围：0x4E00 ord(字符) 0x9FA5
def get_chinese_char_count(str_target): count = 0 for item in str_target: if 0x4E00 <= ord(item) <= 0x9FA5: count += 1
return count count = get_chinese_char_count("a你sid你f好ln") print(count)
# 5. 扩展练习(定义函数，返回指定范围内的素数) # 例如：１－－１００
# 方法１：传统方法 # def get_prime(bengin,end): # list_prime = [] # for number in range(bengin,end+1): # if number < 2: # pass # else: # for i in range(2, number): # if number % i == 0: # break # 如果有结论了,就不需要在和后面的数字比较了 # else: # list_prime.append(number) # return list_prime
# 方法２：自定义函数相互之间嵌套法
def get_prime(bengin, end): """ 生成指定范围内的所有素数 :param bengin: 开始 :param end: 结束 :return: 范围内的所有素数 """ list_prime = [] for number in range(bengin, end + 1): if is_prime(number): list_prime.append(number) return list_prime def is_prime(number): """ 判断是否为素数 :param number: 需要判断的数 :return: 是不是素数 """
if number < 2: return False # 不是素数
# 判断能否被中间的数字整除
for i in range(2, number): if number % i == 0: return False # 不是素数
return True # 是素数
primes = get_prime(5, 100) print(primes) primes = get_prime(-5, 50) print(primes)
五、函数重构代码思想
案例：未重构前代码如下
shang_pin_info = { 101: {"name": "屠龙刀", "price": 10000}, 102: {"name": "倚天剑", "price": 10000}, 103: {"name": "九阴白骨爪", "price": 8000}, 104: {"name": "九阳神功", "price": 9000}, 105: {"name": "降龙十八掌", "price": 8000}, 106: {"name": "乾坤大挪移", "price": 10000} } ding_dan = [] def gou_wu(): """ 购物 :return: """
while True: item = input("1键购买，2键结算。") if item == "1": for key, value in shang_pin_info.items(): print("编号：%d，名称：%s，单价：%d。" % (key, value["name"], value["price"])) while True: cid = int(input("请输入商品编号：")) if cid in shang_pin_info: break
else: print("该商品不存在") count = int(input("请输入购买数量：")) ding_dan.append({"cid": cid, "count": count}) print("添加到购物车。") elif item == "2": zong_jia = 0 for item in ding_dan: shang_pin = shang_pin_info[item["cid"]] print("商品：%s，单价：%d,数量:%d." % (shang_pin["name"], shang_pin["price"], item["count"])) zong_jia += shang_pin["price"] * item["count"] while True: qian = float(input("总价%d元，请输入金额：" % zong_jia)) if qian >= zong_jia: print("购买成功，找回：%d元。" % (qian - zong_jia)) ding_dan.clear() break
else: print("金额不足.") gou_wu()
重构后代码如下：
dict_commodity_info = { 101: {"name": "屠龙刀", "price": 10000}, 102: {"name": "倚天剑", "price": 10000}, 103: {"name": "九阴白骨爪", "price": 8000}, 104: {"name": "九阳神功", "price": 9000}, 105: {"name": "降龙十八掌", "price": 8000}, 106: {"name": "乾坤大挪移", "price": 10000} } list_order = [] def select_menu(): """ 菜单选择 """
while True: item = input("1键购买，2键结算。") if item == "1": buying() elif item == "2": settlement() def settlement(): """ 结算 :return: """ print_order() total_price = get_total_price() pay(total_price) def pay(total_price): """ 支付 :param total_price: 需要支付的价格 :return: """
while True: money = float(input("总价%d元，请输入金额：" % total_price)) if money >= total_price: print("购买成功，找回：%d元。" % (money - total_price)) list_order.clear() break
else: print("金额不足.") def print_order(): """ 打印订单 :return: """
for item in list_order: commodity = dict_commodity_info[item["cid"]] print("商品：%s，单价：%d,数量:%d." % (commodity["name"], commodity["price"], item["count"])) def get_total_price(): """ 计算总价 :return: """ total_price = 0 for item in list_order: commodity = dict_commodity_info[item["cid"]] total_price += commodity["price"] * item["count"] return total_price def buying(): """ 购买 :return: """ print_commodity() order = create_order() list_order.append(order) print("添加到购物车。") def create_order(): """ 创建订单 :return: """
while True: cid = int(input("请输入商品编号：")) if cid in dict_commodity_info: break
else: print("该商品不存在") count = int(input("请输入购买数量：")) return {"cid": cid, "count": count} def print_commodity(): """ 打印商品 :return: """
for key, value in dict_commodity_info.items(): print("编号：%d，名称：%s，单价：%d。" % (key, value["name"], value["price"])) # 程序入口
select_menu()
注：虽然代码量变大了，但是在项目编程时，逻辑更清晰，维护更便捷
六、函数内存图示例（即可变／不可变类型在传参时的区别）：
示例1：
""" 内存图1.0 不可变对象传参 """
def fun01(num01): num01 = 2
print("num01:" + str(num01))# 2
number01 = 1
# 调用方法,在内存中开辟空间(栈帧) # 栈帧中定义该方法内部创建的变量 # 方法执行完毕后，栈帧立即释放．
fun01(number01) print("number01:" + str(number01))# 1
示例2：
""" 内存图2.0 可变对象传参 """
def fun01(list_target): list_target[0] = 2
print("list_target[0]:" + str(list_target[0])) list_number = [1,2] fun01(list_number) print("list_number:" + str(list_number[0]))
示例3
def fun01(a,b,c): a = 100
# 修改的是列表对象，
b[0] = 200
# 修改的是栈帧中的变量
c = 300 num01 = 1 list01 = [2] list02 = [3] fun01(num01,list01,list02) print(num01)#? 1
print(list01)#? [２００]
print(list02)#? [３]
七、2048核心算法：
""" 2048 核心算法:降維 """ # 练习１：定义函数，将零元素移动到末尾 # [2,0,2,0] --> [2,2,0,0] # [0,2,2,0] --> [2,2,0,0] # [0,4,2,4] --> [4,2,4,0] """ 方案１ def zero_to_end(list_target): # １．将传入的列表中非零元素，拷贝到新列表中． # [2, 0, 2, 0] --> [2,2] --> [2,2,0,0] # [0, 4, 2, 4] -->[4, 2, 4] -->[4, 2, 4 ,0] # 2. 根据为零元素的数量，在新列表中添加零元素 # [2, 0, 2, 0] --> [2,2] new_list = [item for item in list_target if item != 0] # [2, 2] --> [2,2,0,0] new_list += [0] * list_target.count(0) # 3. 将新列表中元素赋值给传入的列表 list_target[:] = new_list """ # 方案2 def zero_to_end(list_target): # 从后往前判断，如果零元素，则删除，在末尾追加零元素 # [2, 0, 2, 0] --> [2, 2] --> [2, 2,0,0] for i in range(len(list_target) - 1, -1, -1): if list_target[i] == 0: del list_target[i] list_target.append(0) # list01 = [2, 0, 2, 0] # zero_to_end(list01) # print(list01) # 练习２：定义合并函数 # [2,2,0,0] --> [4,0,0,0] # [2,0,2,0] --> [4,0,0,0] # [2,0,0,2] --> [4,0,0,0] # [2,2,2,0] --> [4,2,0,0] def merge(list_target): # [2,0,2,0] --> [2,2,0,0] [2,2,2,0] zero_to_end(list_target) # [2,2,0,0] --> [4,0,0,0] [4,0,2,0] for i in range(len(list_target) -1): # 相邻且相同 if list_target[i] == list_target[i+1]: list_target[i] += list_target[i+1] list_target[i+1] = 0 zero_to_end(list_target)# [4,0,2,0] --> [4,2,0,0] # list01 = [2,2,2,0] # merge(list01) # print(list01) # 练习３：将二维列表，以表格的格式显示在控制台中 list01 = [ [2,0,0,2], [2,2,0,0], [2,0,4,4], [4,0,0,2], ] def print_map(map): for r in range(len(map)): for c in range(len(map[r])): print(map[r][c],end = " ") print() # print_map(list01) #练习４：定义向左移动函数．１１：５０ """ [2,0,0,2] [4,0,0,0] [2,2,0,0] [4,0,0,0] [2,0,4,4] [2,8,0,0] [4,0,0,2] [4,2,0,0] """ def move_left(map): # 获取第行 for r in range(len(map)): # 从左往右获取行 # 交给merge进行合并 merge(map[r]) def move_right(map): # 获取第行 for r in range(len(map)): # 从右往左获取行 # 交给merge进行合并 list_merge = map[r][::-1] merge(list_merge) map[r][::-1] = list_merge # 作业１：定义向上移动函数 # 从上往下获取列 # 交给合并方法 # 还给原列 # 作业２：定义向下移动函数 # 从下往上获取列 # 交给合并方法 # 还给原列 def move_up(list_target): list_merge = [] for c in range(len(list_target[0])): for r in range(len(list_target)): list_merge.append(list_target[r][c]) merge(list_merge) for r in range(len(list_target)): list_target[r][c] = list_merge[r] list_merge = [] def move_down(list_target): list_merge = [] for c in range(len(list_target[0])): for r in range(len(list_target) - 1, -1, -1): list_merge.append(list_target[r][c]) merge(list_merge) for r in range(len(list_target)): list_target[r][c] = list_merge[3 - r] list_merge = [] # move_left(list01) # move_right(list01) # move_up(list01) move_down(list01) print_map(list01)