python float格式怪异? [英] python float formatting weirdness?

问题描述

我正在尝试调试两个执行非常相似代码的不同python脚本.这些脚本设置a，这是一个简单的浮点数.

I'm trying to debug two different python scripts that execute very similar code. These scripts set a, which is a simple float.

对于脚本1:

ipdb> print sys.version
2.7 (r27:82500, Jul 15 2010, 13:04:38)
[GCC 4.1.2 20071124 (Red Hat 4.1.2-42)]
ipdb> type(a)
<type 'float'>
ipdb> print a
17.23105
ipdb> print '{0:.4f}'.format(a)
17.2311

对于脚本2:

ipdb> print sys.version
2.7 (r27:82500, Jul 15 2010, 13:04:38)
ipdb> print type(a)
<type 'float'>
ipdb> print a
17.23105
ipdb> print '{0:.4f}'.format(a)
17.2310

在两种情况下a如何设置不同的格式?如果我已经检查过17.23105的值是否相同，则两个脚本之间的a可能以什么方式不同? (不幸的是，最初设置a的python代码非常非常长...我不想让每个人都厌烦1000多个行)

How is it possible that a formats differently in the two cases? In what ways can a possibly differ between the two scripts, if I've already checked that their value is the same at 17.23105 ? (unfortunately the python code that originally sets a is very, very long... I wouldn't want to bore everyone with 1000+ lines)

推荐答案

浮点数的str表示形式在Python 2上被截断为12位数字.这很不幸.您必须print repr(a)以确保看到足够的精度来唯一标识浮点数.可能只有微小的差异，只有12位数字才能显示出来.

The str representation of a float truncates to 12 digits on Python 2. This is unfortunate. You have to print repr(a) to make sure you see enough precision to uniquely identify the float. There's probably a tiny difference that only shows up after 12 digits.

在Python 3上，str和repr会为浮点数生成相同的输出，因此不会出现此问题.

On Python 3, str and repr produce the same output for floats, so you wouldn't have this problem.

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