When is method chaining okay in Python?

For a file, the main issue is managing the file handle. Prefer a with block, which closes it reliably when the block ends:

with file_name.open() as f:    data = f.read()

You can chain methods when you do not need the intermediate result, but opening a resource has a lifetime to manage. A temporary variable is not a substitute for proper cleanup.

That one-line form is method chaining. It can be perfectly readable when each call is simple and the return values are predictable. But each extra step can make debugging harder: you cannot easily inspect the intermediate value or put a breakpoint between calls.

So I would not ban chaining. I would split a chain when it gets dense, when you need to handle an intermediate result, or when that makes the code clearer.

A variable is useful when you need to use the result again, give it a meaningful name, or do more work with it. If the next call is all you need, chaining is often fine. In this file example, though, use a context manager rather than relying on the file object being cleaned up later.

There is a practical readability angle too. A short chain like text.strip().lower() is easy to follow. A long chain that keeps changing what kind of object it returns can be much harder to scan, and splitting it gives you places to check results or handle failures.

Use the form that makes the steps easiest to understand, not the one with the fewest lines.