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How to read specific lines from a file by line number in Python

In Python, you can read specific lines from a file by line number using a context manager and the enumerate() function. Here's an example that demonstrates how to read lines 2, 4, and 7 from a file named "example.txt":

def read_specific_lines(filename, line_numbers):
    lines_to_read = set(line_numbers)  # Convert to a set for faster look-up
    lines = []

    with open(filename, 'r') as file:
        for i, line in enumerate(file, start=1):
            if i in lines_to_read:
                lines.append(line.strip())  # Remove leading/trailing whitespaces, including newlines
                lines_to_read.remove(i)  # Remove the line number from the set
                if not lines_to_read:
                    break  # Exit the loop if all desired lines have been read

    return lines

# Example usage
filename = "example.txt"
line_numbers = [2, 4, 7]
specific_lines = read_specific_lines(filename, line_numbers)
print(specific_lines)

In this example, the read_specific_lines function takes a filename and a list of line numbers as arguments. It reads the specified lines from the file and returns them as a list of strings. The enumerate() function is used to track the current line number while reading the file, and the start=1 parameter ensures that line numbering starts at 1.

Accessing lines by line number in Python file:

Description: Demonstrates how to access specific lines in a file by line number.

Code:

line_number = 3
with open('sample.txt', 'r') as file:
    lines = file.readlines()
    if 1 <= line_number <= len(lines):
        specific_line = lines[line_number - 1]
        print(specific_line)

How to read line by line from a file in Python:
- Description: Reading a file line by line using a loop.
- Code:
```
with open('sample.txt', 'r') as file:
    for line in file:
        print(line.strip())
```

Python read specific line number from a text file:

Description: Reading a specific line number from a text file.

Code:

line_number = 2
with open('sample.txt', 'r') as file:
    specific_line = next(islice(file, line_number - 1, line_number), None)
    if specific_line:
        print(specific_line.strip())

Read Nth line from a file in Python:

Description: Reading the Nth line from a file using islice.

Code:

from itertools import islice

line_number = 5
with open('sample.txt', 'r') as file:
    nth_line = next(islice(file, line_number - 1, line_number), None)
    if nth_line:
        print(nth_line.strip())

Extracting lines by line number in Python:

Description: Extracting lines by line number using list comprehension.

Code:

line_numbers = [2, 4, 6]
with open('sample.txt', 'r') as file:
    lines = [line.strip() for i, line in enumerate(file, start=1) if i in line_numbers]
    print(lines)

Accessing specific lines from a file using line number in Python:

Description: Accessing specific lines from a file using a function.

Code:

def get_lines_by_number(file_path, line_numbers):
    with open(file_path, 'r') as file:
        lines = [line.strip() for i, line in enumerate(file, start=1) if i in line_numbers]
    return lines

line_numbers = [2, 4, 6]
result = get_lines_by_number('sample.txt', line_numbers)
print(result)

Read lines by line number with seek() in Python:

Description: Reading lines by seeking to specific positions in a file.

Code:

line_number = 3
with open('sample.txt', 'r') as file:
    file.seek(0)
    specific_line = file.readline()  # Read the first line
    for _ in range(line_number - 1):
        file.readline()  # Move to the desired line
    specific_line = file.readline()
    print(specific_line.strip())

Python read specific line from a large file efficiently:

Description: Efficiently reading a specific line from a large file using islice.

Code:

from itertools import islice

line_number = 500
with open('large_file.txt', 'r') as file:
    specific_line = next(islice(file, line_number - 1, line_number), None)
    if specific_line:
        print(specific_line.strip())

Using readline() and line number to read specific lines in Python:

Description: Using readline() and line number to read specific lines.

Code:

line_number = 3
with open('sample.txt', 'r') as file:
    for _ in range(line_number - 1):
        file.readline()
    specific_line = file.readline()
    print(specific_line.strip())

Read specific line from a text file using linecache in Python:
- Description: Reading a specific line from a text file using the linecache module.
- Code:
```
import linecache

line_number = 3
specific_line = linecache.getline('sample.txt', line_number)
print(specific_line.strip())
```

Accessing lines by index in Python file:

Description: Accessing lines by index using a function.

Code:

def get_line_by_index(file_path, line_index):
    with open(file_path, 'r') as file:
        lines = file.readlines()
        if 0 <= line_index < len(lines):
            return lines[line_index].strip()
        return None

line_index = 2
result = get_line_by_index('sample.txt', line_index)
print(result)

Read specific lines from a file without loading the entire file in Python:

Description: Reading specific lines without loading the entire file into memory.

Code:

line_numbers = [2, 4, 6]
with open('sample.txt', 'r') as file:
    lines = [linecache.getline('sample.txt', i).strip() for i in line_numbers]
    print(lines)

How to extract specific lines using line number in Python:

Description: Extracting specific lines using a list comprehension.

Code:

line_numbers = [2, 4, 6]
with open('sample.txt', 'r') as file:
    lines = [line.strip() for i, line in enumerate(file, start=1) if i in line_numbers]
    print(lines)

Read lines by line number with enumerate() in Python:

Description: Reading lines by line number using enumerate().

Code:

line_numbers = [2, 4, 6]
with open('sample.txt', 'r') as file:
    lines = [line.strip() for i, line in enumerate(file, start=1) if i in line_numbers]
    print(lines)

Python file input/output for reading specific lines:

Description: Reading specific lines from a file using file I/O operations.

Code:

line_numbers = [2, 4, 6]
lines = []

with open('sample.txt', 'r') as file:
    for i, line in enumerate(file, start=1):
        if i in line_numbers:
            lines.append(line.strip())

print(lines)

Efficiently read specific lines from a large file in Python:

Description: Efficiently reading specific lines from a large file.

Code:

line_numbers = [500, 1000, 1500]
with open('large_file.txt', 'r') as file:
    lines = [linecache.getline('large_file.txt', i).strip() for i in line_numbers]
    print(lines)

Accessing lines by index with islice() in Python:

Description: Accessing lines by index using islice for efficient slicing.

Code:

from itertools import islice

line_indices = [1, 3, 5]
with open('sample.txt', 'r') as file:
    lines = list(islice(file, max(line_indices)))
    specific_lines = [line.strip() for i, line in enumerate(lines, start=1) if i in line_indices]
    print(specific_lines)

Read specific lines from a file with open() and readlines() in Python:

Description: Reading specific lines from a file using open() and readlines().

Code:

line_numbers = [2, 4, 6]
with open('sample.txt', 'r') as file:
    lines = file.readlines()
    specific_lines = [lines[i - 1].strip() for i in line_numbers]
    print(specific_lines)

Extracting lines using list comprehension and line number in Python:

Description: Extracting lines using list comprehension and line number.

Code:

line_numbers = [2, 4, 6]
with open('sample.txt', 'r') as file:
    lines = [line.strip() for i, line in enumerate(file, start=1) if i in line_numbers]
    print(lines)