• python学习笔记(十二)之函数


    牛刀小试:

      定义一个无参函数

    1 >>> def myFirstFunc():
    2 ...     print("Hello python")
    3 ...     print("hello world")
    4 ...     print("hello my fist func")
    5 ... 
    6 >>> myFirstFunc()
    7 Hello python
    8 hello world
    9 hello my fist func
    View Code

      定义一个有参函数

    1 >>> def mySecondFunc(name):
    2 ...     print("hello", name)
    3 ... 
    4 >>> mySecondFunc('zhz')
    5 hello zhz
    View Code

    函数之形参和实参

    1 >>> def add(first, second):
    2 ...     return first + second
    3 ... 
    4 >>> add(1, 5)
    5 6
    View Code

    定义函数时,first和second就是形参,在函数调用时,传递的1和5就是实参。

    函数之注释和文档

    1 >>> def add(first,second):
    2 ...     '这是函数文档:计算两个参数的和'
    3 ...     #这是函数注释:计算两个参数的和
    4 ...     return first + second
    5 ... 
    View Code

    函数文档可以使用以下方式查看

    1 >>> add.__doc__
    2 '这是函数文档:计算两个参数的和'
    3 
    4 >>> help(add)
    5 
    6 Help on function add in module __main__:
    7 
    8 add(first, second)
    9     这是函数文档:计算两个参数的和
    View Code

     函数之关键字参数

    1 >>> def saysome(name, words):
    2 ...     print(name, '->', words)
    3 ... 
    4 >>> saysome('Jobs', 'stay hungry,stay foolish')
    5 Jobs -> stay hungry,stay foolish
    6 >>> saysome('stay hungry,stay foolish','Jobs')
    7 stay hungry,stay foolish -> Jobs
    8 >>> saysome(words = 'stay hungry,stay foolish',name = 'Jobs')
    9 Jobs -> stay hungry,stay foolish
    View Code

    函数之默认参数

     1 >>> def saysome(name = 'Jobs', words = 'stay hungry, stay foolish'):
     2 ...     print(name, '->', words)
     3 ... 
     4 >>> saysome()
     5 Jobs -> stay hungry, stay foolish
     6 >>> saysome('nazi')
     7 nazi -> stay hungry, stay foolish
     8 >>> saysome(words = 'keep working')
     9 Jobs -> keep working
    10 >>> saysome('nazi','keep looking')
    11 nazi -> keep looking
    View Code

    函数之收集参数

    1 >>> def test(*params):
    2 ...     for i in range(len(params)):
    3 ...             print(params[i])
    4 ... 
    5 >>> test(1, 'hello', (1,3, ['abc']))
    6 1
    7 hello
    8 (1, 3, ['abc'])
    View Code

    收集参数后最好使用默认参数,用关键字参数调用。

    函数返回值

      python中,用return语句可以从函数返回一个对象,列表或元组。当没有显示调用return语句时,python会自动返回一个NoneType对象。所以,可以说python中只有函数,没有过程。

     1 >>> def hello():
     2 ...     print("Hello")
     3 ... 
     4 >>> temp = hello()
     5 Hello
     6 >>> print(temp)
     7 None
     8 >>> type(temp)
     9 <class 'NoneType'>
    10 >>> def back():
    11 ...     return 1,2,'abc',[1,2]
    12 ... 
    13 >>> back()
    14 (1, 2, 'abc', [1, 2])
    15 >>> def back():
    16 ...     return [1, 3.14, 'abv', [2]]
    17 ... 
    18 >>> back()
    19 [1, 3.14, 'abv', [2]]
    View Code

    局部变量和全局变量

      在函数内部声明的变量是局部变量,在函数外声明的变量是全局变量。

     1 def discount(price,rate):
     2     'final_price, price, rate are local variables'
     3     final_price = price * rate
     4     return final_price
     5     
     6 if __name__ == '__main__':
     7     'old_price, rate and new_price are global variables'
     8     old_price = float(input("原价:"))
     9     rate = float(input("折扣:"))
    10     new_price = discount(old_price, rate)
    11     print("折后价:", new_price)
    View Code

      在函数中试图修改一个全局变量的值时,会python创建一个和全局变量相同的局部变量,此时,修改的只是该局部变量,全局变量不变。

    1 >>> number = 10
    2 >>> def test():
    3 ...     number = 5
    4 ...     
    5 ... 
    6 >>> test()
    7 >>> number
    8 10
    View Code

      要在函数内部修改全局变量的值,可以使用global关键字。

    1 >>> number
    2 10
    3 >>> def test():
    4 ...     global number
    5 ...     number = 5
    6 ... 
    7 >>> test()
    8 >>> number
    9 5
    View Code

    内嵌函数

      在函数内部可以定义其他函数,这个内部函数的作用域仅限于外部函数内部。在外部函数外部的任何位置使用该内部函数,都会抛出一个异常。

     1 >>> def funA():
     2 ...     print("funA")
     3 ...     def funB():
     4 ...             print("funB")
     5 ...     funB()
     6 ... 
     7 >>> funA()
     8 funA
     9 funB
    10 >>> funB()
    11 Traceback (most recent call last):
    12   File "<stdin>", line 1, in <module>
    13 NameError: name 'funB' is not defined
    View Code

    闭包

      如果在一个内部函数里对外部作用域(非全局作用域)的变量进行引用,那么内部函数被认为是一个闭包。

     1 >>> def funX(x):
     2 ...     def funY(y):
     3 ...             return x*y
     4 ...     return funY
     5 ... 
     6 >>> i = funX(5)
     7 >>> type(i)
     8 <class 'function'>
     9 >>> i(6)
    10 30
    11 >>> funX(5)(6)
    12 30
    View Code

      同样的,在闭包内修改外部作用域变量,系统会自动创建局部变量x,屏蔽外部变量。

     1 >>> def fun1():
     2 ...     x = 5
     3 ...     def fun2():
     4 ...             x *= x
     5 ...     fun2()
     6 ... 
     7 >>> fun1()
     8 Traceback (most recent call last):
     9   File "<stdin>", line 1, in <module>
    10   File "<stdin>", line 5, in fun1
    11   File "<stdin>", line 4, in fun2
    12 UnboundLocalError: local variable 'x' referenced before assignment
    View Code

      此时要修改外部变量,一,可以使用列表,列表不是放在栈里。

    1 >>> def fun1():
    2 ...     x = [5]
    3 ...     def fun2():
    4 ...             x[0] *= x[0]
    5 ...     fun2()
    6 ...     print(x)
    7 ... 
    8 >>> fun1()
    9 [25]
    View Code

      二,可以使用nolocal关键字

     1 def fun1():
     2     x = 5
     3     def fun2():
     4         nonlocal x
     5         x = 50
     6     fun2()
     7     print(x)
     8 
     9 if __name__ == '__main__':
    10     fun1()
    View Code
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  • 原文地址:https://www.cnblogs.com/ZGreMount/p/7762524.html
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