搜索文件中的定界字符串-Python

Question

I have the following read.json file

{:{"JOL":"EuXaqHIbfEDyvph%2BMHPdCOJWMDPD%2BGG2xf0u0mP9Vb4YMFr6v5TJzWlSqq6VL0hXy07VDkWHHcq3At0SKVUrRA7shgTvmKVbjhEazRqHpvs%3D-%1E2D%TL/xs23EWsc40fWD.tr","LAPTOP":"error"}

and python script :

import re

shakes = open("read.json", "r")
needed = open("needed.txt", "w")
for text in shakes:
    if re.search('JOL":"(.+?).tr', text):
         print >> needed, text,

I want it to find what's between two words (JOL":" and .tr) and then print it. But all it does is printing all the text set in "read.json".

Answer 1

You're calling re.search , but you're not doing anything with the returned match, except to check that there is one. Instead, you're just printing out the original text . So of course you get the whole line.

The solution is simple: just store the result of re.search in a variable, so you can use it. For example:

for text in shakes:
    match = re.search('JOL":"(.+?).tr', text)
    if match:
        print >> needed, match.group(1)

In your example, the match is JOL":"EuXaqHIbfEDyvph%2BMHPdCOJWMDPD%2BGG2xf0u0mP9Vb4YMFr6v5TJzWlSqq6VL0hXy07VDkWHHcq3At0SKVUrRA7shgTvmKVbjhEazRqHpvs%3D-%1E2D%TL/xs23EWsc40fWD.tr , and the first (and only) group in it is EuXaqHIbfEDyvph%2BMHPdCOJWMDPD%2BGG2xf0u0mP9Vb4YMFr6v5TJzWlSqq6VL0hXy07VDkWHHcq3At0SKVUrRA7shgTvmKVbjhEazRqHpvs%3D-%1E2D%TL/xs23EWsc40fWD , which is (I think) what you're looking for.

However, a couple of side notes:

First, . is a special pattern in a regex, so you're actually matching anything up to any character followed by tr , not .tr . For that, escape the . with a \\ . (And, once you start putting backslashes into a regex, use a raw string literal.) So: r'JOL":"(.+?)\\.tr' .

Second, this is making a lot of assumptions about the data that probably aren't warranted. What you really want here is not "everything between JOL":" and .tr ", it's "the value associated with key 'JOL' in the JSON object". The only problem is that this isn't quite a JSON object, because of that prefixed : . Hopefully you know where you got the data from, and therefore what format it's actually in. For example, if you know it's actually a sequence of colon-prefixed JSON objects, the right way to parse it is:

d = json.loads(text[1:])
if 'JOL' in d:
    print >> needed, d['JOL']

Finally, you don't actually have anything named needed in your code; you opened a file named 'needed.txt' , but you called the file object love . If your real code has a similar bug, it's possible that you're overwriting some completely different file over and over, and then looking in needed.txt and seeing nothing changed each time…

Answer 2

If you know that your starting and ending matching strings only appear once, you can ignore that it's JSON. If that's OK, then you can split on the starting characters (JOL":"), take the 2nd element of the split array [1], then split again on the ending characters (.tr) and take the 1st element of the split array [0].

>>> text = '{:{"JOL":"EuXaqHIbfEDyvph%2BMHPdCOJWMDPD%2BGG2xf0u0mP9Vb4YMFr6v5TJzWlSqq6VL0hXy07VDkWHHcq3At0SKVUrRA7shgTvmKVbjhEazRqHpvs%3D-%1E2D%TL/xs23EWsc40fWD.tr","LAPTOP":"error"}'

>>> text.split('JOL":"')[1].split('.tr')[0]

'EuXaqHIbfEDyvph%2BMHPdCOJWMDPD%2BGG2xf0u0mP9Vb4YMFr6v5TJzWlSqq6VL0hXy07VDkWHHcq3At0SKVUrRA7shgTvmKVbjhEazRqHpvs%3D-%1E2D%TL/xs23EWsc40fWD'