如何从python中的文件中提取特定信息

Question

I have a file with following format:

device={
   id=1
   tag=10
   name=device1
}
device={
   id=2
   tag=20
   name=device2
}
device={
   id=3
   tag=30
   name=device3
}

So let's say I am only interested in device with id=2 and I want to extract its tag number(this is configurable and will be changed from some other code). So I need to extract tag number of the device id 2. How can I do this in python. I have done following:

ID='id=2'

with open("file.txt") as file:
          for line in file:
              if line.strip() ==  ID:
                  #Here I do not know what to write 
                  # to extract 20

Thanks

Answer 1

With re.search function:

import re

with open('file.txt', 'r') as f:
    id_num = 'id=2'
    tag_num = re.search(r'' + id_num + '\s+tag=([0-9]+)', f.read())
    print(tag_num.group(1))

The output:

20

---

• f.read() - reads the file contents (as text)

• r'' + id_num + '\\s+tag=([0-9]+)' - constructing regex pattern, so it would become id=2\\s+tag=([0-9]+) where \\s is one or many whitespace characters(including newlines) and ([0-9]+) is the 1st captured group containing tag number

• tag_num.group(1) - extracting the value of the 1st captured/parenthesized group 1 from the match object tag_num

Answer 2

You can read the next line using line.readline() try to use this code:

ID='id=2'

with open("file.txt") as file:
    while True:
        line = file.readline()
        if line.strip() == ID:
            nextline = file.readline()
            result = nextline.strip().split('=')[1]
       if line == '':
            break

Answer 3

with open("") as file:
    #print file.read()

    for line in file:
        #print line.split()
        if line.strip()==ID:
          d=file.next()              #reads next line
          print d.split('=')[1]
          break