Python: 函数详解
一、函数的名称、参数和返回值
def bmi(height, weight):
return round(weight/(height*height),1)
print(bmi(1.6,44)) #17.2round函数返回一个数值，该数值是按照指定的小数位数进行四舍五入运算的结果。
二、Docstring
def bmi(height, weight):
'''
计算BMI的值：
:param height: 1.6m
:param weight: 44kg
:return: weight/(height*height),保留一位小数
'''
return round(weight/(height*height),1)
print(bmi.__doc__)
print(round.__doc__)
print(bmi(1.6,44)) #17.2
print(__doc__) 输出文件开头注释的内容
三、参数（见上一节函数的参数）
def gongxi():
print('恭喜发财！')
gongxi() #恭喜发财！def hello(name,type):
print(f"{name}是一个{type}")
hello('狗','大黄')四、返回值
函数可以有返回值也可以没有，None；遇到return，函数执行结束。
def send_flower(flower_num):
if (flower_num < 10):
return 'NO'
if (flower_num % 14 == 0):
return 'YES'
else:
return 'THANKS'
print(send_flower(18)) #THANKS如果返回多个值，多个值被包在一个元组里面
def bmi(height,weight):
bmi_value = round(weight/(height*height),1)
if(bmi_value < 18.5):
return bmi_value,'多吃点'
elif(bmi_value <= 24):
return bmi_value,'你真棒'
else:
return '谢谢你'
# print(bmi(1.8,60)) #(18.5, '你真棒')
result = bmi(1.8,60)
print(result[1]) #你真棒五、传值与传引用
（1）基本类型是传值，简单复制一份，不影响原来的变量的饿值
height = 1.58
def predict_height(height):
'''预测将来的身高'''
height = height + 0.3
return height
print(predict_height(height))
print(height)
#1.8800000000000001
#1.58（2）复杂类型是传引用，传过去是变量的内存地址，要修改就都修改了
heights = [1.58,1.56,1.87,1.98]
def predict(heights):
for index,h in enumerate(heights):
heights[index] = h +0.3
return heights
future_heights = predict(heights)
print(future_heights)
print(heights)
#[1.8800000000000001, 1.86, 2.17, 2.28]
#[1.8800000000000001, 1.86, 2.17, 2.28]（3）复杂类型如何传值，若仍想保留原来的值，只需要再复制一份
heights = [1.58,1.56,1.87,1.98]
def predict(heights):
for index,h in enumerate(heights):
heights[index] = h +0.3
return heights
future_heights = predict(heights[:])
print(future_heights)
print(heights)
# [1.8800000000000001, 1.86, 2.17, 2.28]
# [1.58, 1.56, 1.87, 1.98]六、函数有自己的属性，可以被赋值，也可以被传递
def bmi(height,weight):
bmi_value = round(weight/(height*height),1)
if(bmi_value < 18.5):
return bmi_value,'多吃点'
elif(bmi_value <= 24):
return bmi_value,'你真棒'
else:
return '谢谢你'
def main(check):
height = float(input('输入身高'))
weight = float(input('输入体重'))
print(check(height,weight))
main(bmi)
# 输入身高1.8
# 输入体重60
# (18.5, '你真棒')七、匿名函数（lambda）
#传统方法
numbers = [2,4,5,6,8,3,6]
def process(numbers):
for n in numbers:
print(n*n,end = ' ')
print()
process(numbers) #4 16 25 36 64 9 36
#匿名函数 lambda
numbers = [2,4,5,6,8,3,6]
def process2(numbers,calc):
for n in numbers:
print(calc(n),end = ' ')
print()
process2(numbers, lambda x:x+5) #7 9 10 11 13 8 11
process2(numbers, lambda x:x if x%3 !=0 else 11) #2 4 5 11 8 11 11八、变量的作用域：全局和局部
局部变量：def 和 class 内定义的变量
全局变量：在脚本内（def 和 class外）定义的变量，可以在global和函数内访问
局部变量和全局变量重名，局部变量优先使用
全局是指在当前文件（模块）内全局
count = 8
def work():
a = 8
count = 10
print(count)
work() #10
print(count) #8九、用global在函数中改写全局变量
count = 8
def work():
global count #这个count就是外面的count
count = 10
print(count)
work() #10
print(count) #10十、import(5种语法)
import method
method.f1()
import method as m2
m2.f1()
from method import f1
f1()
from method import f1 as func1
func1()
from method import *
f1()
f2()
print(a)