本文共 1754 字，大约阅读时间需要 5 分钟。
In Python 3, they made the / operator do a floating-point division, and added the // operator to do integer division (i.e. quotient without remainder); whereas in Python 2, the / operator was simply integer division, unless one of the operands was already a floating point number.
In Python 2.X:
>>> 10/33>>> # to get a floating point number from integer division:>>> 10.0/33.3333333333333335>>> float(10)/33.3333333333333335
In Python 3:
>>> 10/33.3333333333333335>>> 10//33
For further reference, see .
// is unconditionally "truncating division", e.g:
>>> 4.0//1.52.0
As you see, even though both operands are floats, // still truncates -- so you always know securely what it's gonna do.
Single / may or may not truncate depending on Python release, future imports, and even flags on which Python's run, e.g....:
$ python2.6 -Qold -c 'print 2/3'0$ python2.6 -Qnew -c 'print 2/3'0.666666666667
As you see, single / may truncate, or it may return a float, based on completely non-local issues, up to and including the value of the -Q flag...;-).
So, if and when you know you want truncation, always use //, which guarantees it. If and when you know you don't want truncation, slap a float() around other operand and use /. Any other combination, and you're at the mercy of version, imports, and flags!-)
To complement these other answers, the // operator also offers significant (3x) performance benefits over /, presuming you want integer division.
$ python -m timeit '20.5 // 2'100000000 loops, best of 3: 0.0149 usec per loop$ python -m timeit '20.5 / 2'10000000 loops, best of 3: 0.0484 usec per loop$ python -m timeit '20 / 2'10000000 loops, best of 3: 0.043 usec per loop$ python -m timeit '20 // 2'100000000 loops, best of 3: 0.0144 usec per loop
转载地址：http://iihbi.baihongyu.com/