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What is the difference between reading a file with .read(), .readline(), and .readlines()? What are the common file modes ('r', 'w', 'a', 'rb') passed to open(), and what does each one do? How do you write and use a custom context manager by implementing __enter__ and __exit__? How does @contextlib.contextmanager let you write a context manager using a generator function instead of a full class? How do you use pathlib.Path for modern, object-oriented file path manipulation instead of os.path's string-based functions? How do you use multiple context managers in a single 'with' statement, and how does this compare to nesting separate 'with' blocks? How do you check whether a file or directory exists before operating on it, using pathlib? How would you implement a context manager that temporarily changes the current working directory and restores it afterward? How do you implement contextlib.ExitStack to dynamically manage a VARIABLE number of context managers determined at runtime? How would you write a reusable context manager decorator using contextlib.contextmanager that ALSO works when applied directly to a function, like @contextmanager-decorated functions support?
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How do you open and read a text file using the 'with' statement, and why is 'with' preferred over manual open()/close()?

Beginner

Answer

'with open(path) as f:' guarantees the file is properly closed when the block exits, EVEN IF an exception occurs inside it — manually calling open() and close() risks leaking the file handle if an exception happens between them and close() is never reached.
with open("data.txt") as f:
    content = f.read()
print(content)
# file is automatically closed here, even if .read() had raised an exception
Real-world example Reading a configuration or data file safely, guaranteeing the file handle is released even if reading fails partway through.

Common follow-ups: What exception type does open() raise if the specified file doesn't exist?

Exception Handling
All 15 File I/O & Context Managers questions