'is' and '==' in Python

比较字符串的时候发现'is'和'=='在比较字符串的时候的效果是不一样的

http://stackoverflow.com/questions/2988017/string-comparison-in-python-is-vs 里面说

You use == when comparing values and is when comparing identities.

When comparing ints (or immutable types in general), you pretty much always want the former. There's an optimization that allows small integers to be compared with is, but don't rely on it.

For boolean values, you shouldn't be doing comparisons at all. Instead of:

if x ==True:
    # do something

write:

if x:
    # do something

For comparing against None, is None is preferred over == None.

I've always liked to use 'is' because I find it more aesthetically pleasing and pythonic (which is how I fell into this trap...), but I wonder if it's intended to just be reserved for when you care about finding two objects with the same id.

Yes, that's exactly what it's for.

转载于:https://www.cnblogs.com/songzi/archive/2012/02/21/2361844.html