python的三元运算符

Yes, it was added in version 2.5. It's frowned upon by some pythonistas, so keep that in mind.
The syntax is:

a if test else b

First test is evaluated, then either a or b is returned based on the Boolean value of test;
if test evaluates to True a is returned, else b is returned.

For example:

>>> 'true' if True else 'false'
'true'
>>> 'true' if False else 'false'
'false'

Official documentation:

• Conditional expressions
• Is there an equivalent of C’s ”?:” ternary operator?