如何使用Python解析格式化的字符串

Question

The string I want to parse is like "{average:12.1km/ltr}". I want to extract 12.1 from this string. The only way I know is using split(":") and split("km/ltr") or so, but these seem not useful. I want to use the scanf-like method to extract 12.1, but in python document, it shows that using regular expression is better than scanf-like function. I though regular express cannot be used in extraction. How should I extract this using re?

Answer 1

I think you could have simply used the following to extract the numeric portion from the string.

• The Trick is, there is one and only one number with a period between.
• Period may be optional, as you number may be a whole integer
• You may also encounter fractional numbers

Here is the sample

>>> re.findall("\d+\.?\d*|\.\d+",st)
>>> st = "{average:12.1km/ltr}"
>>> re.findall("\d+\.?\d*|\.\d+",st)
['12.1']
>>> st = "{average:12km/ltr}"
>>> re.findall("\d+\.?\d*|\.\d+",st)
['12']
>>> st = "{average:.5km/ltr}"
>>> re.findall("\d+\.?\d*|\.\d+",st)
['.5']
>>> st = "{average:12.km/ltr}"
>>> re.findall("\d+\.?\d*|\.\d+",st)
['12.']
>>> st = " {max:26.9kgm@6100rpm}"
>>> re.findall("\d+\.?\d*|\.\d+",st)
['26.9', '6100']

Answer 2

Just strip all characters you don't want - no need for regular expressions (though I like them...)

>>> import string
>>> s = "{average:12.1km/ltr}"
>>> s2 = s.strip(string.ascii_letters + "{}:/")
>>> print s2
12.1
>>> number = float(s2)
>>> print number
12.1

Answer 3

Try this, assuming the number could be without dot.

import re
re.findall('[0-9]+(\.[0-9]+)?', str)

Answer 4

how about dirty and quick

re.findall('[\d.]+',s)

this works for your example.

Answer 5

You said you tried to split(":") and split("km/ltr") , so I'll suppose that the format of the string is always like :__X__km/ltr , where __X__ is a number.

The following regex will work:

:(\d.+)km

Example:

>>> import re
>>> re.findall(':(\d.+)km', '{average:12.1km/ltr}')
['12.1']
>>>

Then you can just parse as float using the float() function.