Python函数

def function-name(parameters):
    statement(s)

def double(x):
    return x*2

>>> def f(x, y=[]):
...     y.append(x)
...     return y
... 
>>> print(f(23))
[23]
>>> print(f(24))
[23, 24]

>>> def f(x, y=None):
...     if y is None:
...             y=[]
...             y.append(x)
...             return y
...     
>>> print(f(23))
[23]
>>> print(f(24))
[24]