How to extract a number before a certain words?

问题

There is a sentence "i have 5 kg apples and 6 kg pears".

I just want to extract the weight of apples.

So I use

sentence = "I have 5 kg apples and 6 kg pears"
number = re.findall(r'(\d+) kg apples', sentence)
print (number)

However, it just works for integer numbers. So what should I do if the number I want to extract is 5.5?

回答1:

The regex you need should look like this:

(\d+.?\d*) kg apples

You can do as follows:

number = re.findall(r'(\d+.?\d*) kg apples', sentence)

Here is an online example

回答2:

? designates an optional segment of a regex.

re.findall(r'((\d+\.)?\d+)', sentence)

回答3:

You can use number = re.findall(r'(\d+\.?\d*) kg apples', sentence)

回答4:

You change your regex to match it:

(\d+(?:\.\d+)?)

\.\d+ matches a dot followed by at least one digit. I made it optional, because you still want one digit.

回答5:

re.findall(r'[-+]?[0-9]*\.?[0-9]+.', sentence)

回答6:

Non-regex solution

sentence = "I have 5.5 kg apples and 6 kg pears"
words  = sentence.split(" ")

[words[idx-1] for idx, word in enumerate(words) if word == "kg"]
# => ['5.5', '6']

You can then check whether these are valid floats using

try:
   float(element)
except ValueError:
   print "Not a float"

回答7:

You can try something like this:

import re

sentence = ["I have 5.5 kg apples and 6 kg pears",
                   "I have 5 kg apples and 6 kg pears"]
for sen in sentence:
    print re.findall(r'(\d+(?:\.\d+)?) kg apples', sen)

Output:

['5.5']
['5']

来源：https://stackoverflow.com/questions/41356738/how-to-extract-a-number-before-a-certain-words

标签

python

regex