Python's readline() Method Explained

The readline() method in Python is a straightforward yet powerful tool for reading text files line by line. This approach is particularly beneficial for processing large files or analyzing content on a record-by-record basis without loading the entire file into memory.

file.readline()

Imagine you're working with a text file named `poetry.txt`, containing a poem with each verse starting on a new line.

Here’s an effective way to use readline to echo every verse to the console:

with open('poetry.txt', 'r') as file:
    while True:
        # Read a line
        line = file.readline()
        # An empty line indicates the end of the file
        if not line:
            break
        # Output the line, newline character included
        print(line, end='')

Start by opening the file with the open() function in read mode (`'r'`).

Next, employ the readline() method to sequentially read a line at a time. With each invocation, Python fetches the subsequent line from the file.

The print(line, end='') command displays each line without appending an additional newline character, leveraging the fact that readline() already includes a newline character at the end of each line it reads, except for the file's last line if it doesn't end with a newline.

Upon reaching the file's end, readline() returns an empty string (''), serving as a cue to break out of the loop reading the file.

The perpetual while True: loop is cleverly terminated using a break command once readline() signals the file's conclusion with an empty string.

To wrap up, closing the file with the close() method is a best practice, ensuring the release of system resources. However, in this script, the use of a context manager (with open(...) as file:) obviates the need for explicitly closing the file, as it's automatically handled at the end of the block.