【python】入门学习（四）

函数：

定义函数

#area.py

from math import pi

def area(radius):

    """Return the area of a circle with the given radius."""

    return pi * radius ** 2

>>> ================================ RESTART ================================

>>>

>>> area(5.5)

95.03317777109125

>>> print(area.__doc__)

Return the area of a circle with the given radius.

>>>

doctest #可用于自动运行文档字符串中的python示例代码

全局变量访问时一定要加上global

#error

name = 'Jack'

def say_hello():

    print('Hello ' + name + '!')

def change_name(new_name):

    name = new_name

>>> say_hello()

Hello Jack!

>>> change_name('Mary')

>>> say_hello()

Hello Jack!

#correct

name = 'Jack'

def say_hello():

    print('Hello ' + name + '!')

def change_name(new_name):

    global name

    name = new_name

>>> say_hello()

Hello Jack!

>>> change_name('Mary')

>>> say_hello()

Hello Mary!

main():被认为是程序的起点，可选不一定要。运行时必须输入main()

python中参数的传递都是按引用传参，python不支持按值传参

在引用传参中，无法修改参数的值。下面的函数不起作用：

#reference.py

def set1(x):

    x = 1

>>> ================================ RESTART ================================

>>>

>>> y = 5

>>> set1(y)

>>> y

5

函数参数默认值：

注意：包含默认参数的形参一定要放在无默认参数的形参后面

只有第一次调用函数时给默认参数赋值！ #还不理解，先记下来

#greetings.py

def greet(name, greeting = 'Hello'):

    print(greeting, name + '!')

>>> greet('bob')

Hello bob!

>>> greet('bob', 'Good morning')

Good morning bob!

使用关键字传参，即在使用时也指明形参，可以不理会顺序，很好用：

#greetings.py

def greet(name = 'Bob', greeting = 'Hello'):

    print(greeting, name + '!')

>>> greet(greeting = 'Good evening', name = 'Mary')

Good evening Mary!

>>> greet(greeting = 'Good evening')

Good evening Bob!

也可以用模块化的方式来调用，模块中不包括main函数

>>> import greetings

>>> greetings.greet()

Hello Bob!

>>> dir(greetings)

['__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'greet']

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【python】入门学习（四）

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