7 2 3 readlines() Explained

Key Concepts

The readlines() method in Python is used to read all lines from a file and return them as a list of strings. The key concepts include:

• Reading All Lines
• Returning a List of Strings
• Handling Large Files
• Iterating Over Lines

1. Reading All Lines

The readlines() method reads all lines from the file and stores them in a list. Each line in the file becomes an element in the list.

Example:

file = open('example.txt', 'r')
lines = file.readlines()
file.close()

print(lines)  # Output: ['Line 1\n', 'Line 2\n', 'Line 3\n']
    

Analogy: Think of reading a book and storing each page as a separate item in a list.

2. Returning a List of Strings

The readlines() method returns a list where each element is a string representing a line from the file. This makes it easy to manipulate and process each line individually.

Example:

file = open('example.txt', 'r')
lines = file.readlines()
file.close()

for line in lines:
    print(line.strip())  # Output: Line 1, Line 2, Line 3
    

Analogy: Think of each line in the file as a separate piece of text that you can process individually.

3. Handling Large Files

When dealing with large files, using readlines() can consume a lot of memory because it loads all lines into a list. For large files, consider using a loop with readline() or iterating over the file object directly.

Example:

file = open('large_file.txt', 'r')
for line in file:
    print(line.strip())
file.close()
    

Analogy: Think of reading a large book one page at a time instead of trying to store the entire book in memory.

4. Iterating Over Lines

You can iterate over the list returned by readlines() to process each line individually. This is useful for tasks like searching for specific content or performing operations on each line.

Example:

file = open('example.txt', 'r')
lines = file.readlines()
file.close()

for line in lines:
    if 'keyword' in line:
        print(line.strip())
    

Analogy: Think of searching for a specific word in a book by checking each page individually.

Putting It All Together

By understanding and using the readlines() method effectively, you can read and process all lines from a file in Python. This method is particularly useful for smaller files or when you need to manipulate each line individually.

Example:

file = open('example.txt', 'r')
lines = file.readlines()
file.close()

for line in lines:
    print(line.strip())  # Output: Line 1, Line 2, Line 3