How to get an index value based on a string available on that index?

For a given text file (sample.txt), I would like to get index value based on a string that is present on that line (index).

An example file contains following text (sample.txt):

line 1: open a file.

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line 2: Read a file and store it in a variable.

line 3: check condition using ‘in’ operator for string present in the file or not.

line 4: If the condition true print the index in which the string is found.

line 5: Close a file.

if my target string is ‘variable’. The output I would like to have is:
2

>Solution :

This should do:

def indicesOfQueryOnFile(query, file):
    with open(file, 'r') as f:
        cleanLines = [line for line in f.readlines() if len(line.strip()) > 0]
        indices = [i + 1 for i, line in enumerate(cleanLines) if query in line]
    
    return indices

For the text file:

line 1: open a file.

line 2: Read a file and store it in a variable.

line 3: check condition using ‘in’ operator for string present in the file or not.

line 4: If the condition true print the index in which the string is found.

line 5: Close a file.

another line with variable

It would output:

indicesOfQueryOnFile('variable', 'test.txt')
# [2, 6]