定义函数

在Python中,定义一个函数要使用def语句,依次写出函数名,括号,括号中的参数和冒号:,

然后,在缩进块中编写函数体,函数的返回值用return 语句返回。

我们自定义结构求绝对值的my_abc函数示例:

# -*- coding: UTF-8 -*-
def my_abs(x):
    if x >= 0:
        return x
    else:
        return -x
print my_abs(20)


C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/t1.py
20


/***************

# -*- coding: UTF-8 -*-
def my_abs(x):
    if x >= 0:
        return x
    else:
        return
    print  my_abs(-20)
if my_abs(-20):
    print 1111111
else:
    print 2222222



C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/t1.py
2222222


# -*- coding: UTF-8 -*-
def my_abs(x):
    if x >= 0:
        return x
    else:
        return
print     my_abs(-20)

C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/a5.py
None


# -*- coding: UTF-8 -*-
# -*- coding: UTF-8 -*-
def my_abs(x):
    if x >= 0:
        return x
    else:
        return
print     my_abs(-20)
if my_abs(-20):
    print 1111111
else:
    print 2222222



空函数:

如果想定义一个什么事情也不做的空函数,可以用pass语句:

参数检查:

调用函数时,如果参数个数不对,Python解释器会自动检查出来,并抛出TypeError:



# -*- coding: UTF-8 -*-
def my_abs(x):
    if x >= 0:
        return x
    else:
        return
print     my_abs(-20,1)

C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/t1.py
Traceback (most recent call last):
  File "C:/Users/TLCB/PycharmProjects/untitled/t1.py", line 7, in <module>
    print     my_abs(-20,1)
TypeError: my_abs() takes exactly 1 argument (2 given)