Integer Precision

Division may differ slightly across Python releases, but it’s still fairly standard. Here’s something a bit more exotic. As mentioned earlier, Python 3.0 integers support unlimited size:

>>> 999999999999999999999999999999 + 1
1000000000000000000000000000000

广告：个人专属 VPN，独立 IP，无限流量，多机房切换，还可以屏蔽广告和恶意软件，每月最低仅 5 美元

Python 2.6 has a separate type for long integers, but it automatically converts any number too large to store in a normal integer to this type. Hence, you don’t need to code any special syntax to use longs, and the only way you can tell that you’re using 2.6 longs is that they print with a trailing “L”:

>>> 999999999999999999999999999999 + 1
1000000000000000000000000000000L

Unlimited-precision integers are a convenient built-in tool. For instance, you can use them to count the U.S. national debt in pennies in Python directly (if you are so inclined, and have enough memory on your computer for this year’s budget!). They are also why we were able to raise 2 to such large powers in the examples in Chapter 3. Here are the 3.0 and 2.6 cases:

>>> 2 ** 200
1606938044258990275541962092341162602522202993782792835301376

>>> 2 ** 200
1606938044258990275541962092341162602522202993782792835301376L

Because Python must do extra work to support their extended precision, integer math is usually substantially slower than normal when numbers grow large. However, if you need the precision, the fact that it’s built in for you to use will likely outweigh its performance penalty.