你可以这样使用字符串格式化操作符:

num = 49
x = "%.2f" % num  # x is now the string "49.00"

我不确定您所说的“高效”是什么意思——这几乎肯定不是应用程序的瓶颈。如果您的程序运行缓慢，请先对其进行分析，以找到热点，然后优化这些热点。

Python文档中的字符串格式化操作部分包含了您正在寻找的答案。简而言之:

"%0.2f" % (num,)

一些例子:

>>> "%0.2f" % 10
'10.00'
>>> "%0.2f" % 1000
'1000.00'
>>> "%0.2f" % 10.1
'10.10'
>>> "%0.2f" % 10.120
'10.12'
>>> "%0.2f" % 10.126
'10.13'

你应该使用新的格式规范来定义你的值应该如何表示:

>>> from math import pi  # pi ~ 3.141592653589793
>>> '{0:.2f}'.format(pi)
'3.14'

文档有时可能有点迟钝，所以我推荐以下更容易阅读的参考:

Python字符串格式烹饪书:展示了新风格的.format()字符串格式的示例 Pyformat.info:比较老式的%字符串格式和新式的.format()字符串格式

Python 3.6引入了字面值字符串插值(也称为f-strings)，所以现在你可以把上面的代码写得更简洁:

>>> f'{pi:.2f}'
'3.14'

>>> print "{:.2f}".format(1.123456)
1.12

你可以把2f中的2改成你想显示的任何小数点。

编辑:

在Python3.6中，它转换为:

>>> print(f"{1.1234:.2f}")
1.12

你可以这样使用字符串格式化操作符:

num = 49
x = "%.2f" % num  # x is now the string "49.00"

我不确定您所说的“高效”是什么意思——这几乎肯定不是应用程序的瓶颈。如果您的程序运行缓慢，请先对其进行分析，以找到热点，然后优化这些热点。

如果你用这个来表示货币，并且还想用's来分隔值，你可以使用's

$ {:, .f2} .format (currency_value)。

例如:

Currency_value = 1234.50

$ {:，.f2}.format(currency_value)——> $ 1,234.50

下面是我不久前写的一段代码:

print(">在年底" + year_string + " total paid is \t$ {:，.2f}".format(total_paid))

> At the end of year   1  total paid is         $ 43,806.36
> At the end of year   2  total paid is         $ 87,612.72
> At the end of year   3  total paid is         $ 131,419.08
> At the end of year   4  total paid is         $ 175,225.44
> At the end of year   5  total paid is         $ 219,031.80   <-- Note .80 and not .8
> At the end of year   6  total paid is         $ 262,838.16
> At the end of year   7  total paid is         $ 306,644.52
> At the end of year   8  total paid is         $ 350,450.88
> At the end of year   9  total paid is         $ 394,257.24
> At the end of year  10  total paid is         $ 438,063.60   <-- Note .60 and not .6
> At the end of year  11  total paid is         $ 481,869.96
> At the end of year  12  total paid is         $ 525,676.32
> At the end of year  13  total paid is         $ 569,482.68
> At the end of year  14  total paid is         $ 613,289.04
> At the end of year  15  total paid is         $ 657,095.40   <-- Note .40 and not .4  
> At the end of year  16  total paid is         $ 700,901.76
> At the end of year  17  total paid is         $ 744,708.12
> At the end of year  18  total paid is         $ 788,514.48
> At the end of year  19  total paid is         $ 832,320.84
> At the end of year  20  total paid is         $ 876,127.20   <-- Note .20 and not .2