Search external file for specific word and store the very next word in variable in Python

Question

I have a file that has a line similar to this:

"string" "playbackOptions -min 1 -max 57 -ast 1 -aet 57

now i want to search the file and extract and store the value after " -aet" (in this case 57) in a variable.

I'm using

import mmap

with open('file.txt') as f:
    s = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ)
    if s.find('-aet') != -1:
        print('true')

for searching. but can't go beyond this.

Answer 1

I suggest to use regular expressions to extract the values:

import re

# Open the file for reading
with open("file.txt", "r") as f:
    # Loop through all the lines:
    for line in f:
        # Find an exact match
        # ".*" skips other options,
        # (?P<aet_value>\d+) makes a search group named "aet_value"
        # if you need other values from that line just add them here
        line_match = re.search(r"\"string\" \"playbackOptions .* -aet (?P<aet_value>\d+)", line)
        # No match, search next line
        if not line_match:
            continue
        # We know it's a number so it's safe to convert to int
        aet_value = int(line_match.group("aet_value"))
        # Do whatever you need
        print("Found aet_value: {}".format(aet_value)

Answer 2

Here's another approach using native string and list methods, as I usually forget regex syntax when I haven't touched it in a while:

tag = "-aet"  # Define what tag we're looking for.

with open("file.txt", "r") as f:  # Read file.
    for line in f:  # Loop through every line.
        line_split = line.split()  # Split line by whitespace.

        if tag in line_split and line_split[-1] != tag:  # Check if the tag exists and that it's not the last element.
            try:
                index = line_split.index(tag) + 1  # Get the tag's index and increase by one to get its value.
                value = int(line_split[index])  # Convert string to int.
            except ValueError:
                continue  # We use try/except in case the value cannot be cast to an int. This may be omitted if the data is reliable.

            print value  # Now you have the value.

It would be interesting to benchmark but typically regex is slower, so this may perform faster especially if the file is particularly big.