7 2 2 readline() Explained

Key Concepts

The readline() method in Python is used to read a single line from a file. The key concepts include:

• Reading a Single Line
• Handling End of File (EOF)
• Reading Multiple Lines
• Combining with Other File Operations

1. Reading a Single Line

The readline() method reads a single line from the file. It stops reading at the end of the line, which is marked by a newline character (\n).

Example:

with open('example.txt', 'r') as file:
    line = file.readline()
    print(line)
    

Analogy: Think of readline() as reading a single sentence from a paragraph, where each sentence ends with a period.

2. Handling End of File (EOF)

When the end of the file is reached, readline() returns an empty string. This can be used to detect the end of the file.

Example:

with open('example.txt', 'r') as file:
    while True:
        line = file.readline()
        if not line:
            break
        print(line)
    

Analogy: Think of EOF as the end of a book. When you reach the last page, there are no more sentences to read.

3. Reading Multiple Lines

You can use a loop to read multiple lines from a file. Each call to readline() reads the next line in the file.

Example:

with open('example.txt', 'r') as file:
    while True:
        line = file.readline()
        if not line:
            break
        print(line)
    

Analogy: Think of reading multiple lines as reading multiple sentences from a paragraph, one by one.

4. Combining with Other File Operations

The readline() method can be combined with other file operations, such as writing to a file or processing the data before writing it.

Example:

with open('example.txt', 'r') as file:
    with open('output.txt', 'w') as output_file:
        while True:
            line = file.readline()
            if not line:
                break
            processed_line = line.upper()
            output_file.write(processed_line)
    

Analogy: Think of combining readline() with other operations as reading a sentence, processing it (like converting it to uppercase), and then writing it to another document.

Putting It All Together

By understanding and using the readline() method effectively, you can read and process data line by line from a file. This method is particularly useful for handling large files or when you need to process data sequentially.

Example:

with open('example.txt', 'r') as file:
    with open('output.txt', 'w') as output_file:
        while True:
            line = file.readline()
            if not line:
                break
            processed_line = line.strip().upper()
            output_file.write(processed_line + '\n')