python之语句mode = 'test' if y is None else 'train'

python之语句mode = ‘test’ if y is None else ‘train’

语句：mode = ‘test’ if y is None else ‘train’
相当于：

if y==None:
	mode='test'
else:
	mode='train'

具体示例如下：

>>> def func(y):
...     if y==None:
...             mode='test'
...     else:
...             mode='train'
...     return mode
... 
>>> y
1
>>> mode=func(y)
>>> mode
'train'
>>> y=None
>>> mode=func(y)
>>> mode
'test'
>>>