Most idiomatic way to convert None to empty string?

One line idiom: The Pythonista's approach

Python empowers you to write expressive and compact code. The or operator is a shining example of this. It's not just for strings, it can offer default values to many other types:

# You shall not pass (None)
number = num or 0   # 0 to the rescue for numbers
items = lst or []   # Empty list is better than None, at least you can .append() onto it
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It's like going on an efficiency drive, packing your functionality in a compact and easy-to-understand body. It avoids overcomplication and appreciates Python's zen: explicit is better than implicit, but laconic is better than verbose.

Clarity over brevity: The methodical approach

The ternary operator is your friend if you want your intentions to be crystal clear:

safe_text = '' if text is None else text
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This may be slightly verbose, but is as clear as daylight. A pity it doesn't work against zombies, but surely does against None!

Custom function: Because who doesn't like personalized stuff?

In certain scenarios, it may be beneficial to wrap your conversion logic into a custom function:

def xstr(s):
    return '' if s is None else str(s)
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This function, xstr, is a good sign to show that we're preventing None from wreaking havoc. So, putting this line in your code is like putting a sign, "Beware, None shall pass here!".

LAMBDA: The ninja approach

If you like your functions single-lined and sneaky, lambda can help:

xstr = lambda s: str(s or '')
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This lambda function is like a stealthy ninja, doing exactly what xstr does but in a silent, one-line way. Remember, the str function ensures correct conversion for all various data types.

Use the force, but wisely

The or operator can sometimes lead to surprises because it delivers the second operand if the first one is None or evaluates to false. For instance, 0, [], or False would also return the default value:

assert (0 or "default") == "default"  # Jedi trick: None isn't the only one giving you "default"
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To avoid stepping on these hidden rakes, use this pattern only when None is the only thing you wouldn't want around.

Mind the pitfalls

• Wrapping value in str() is an excellent defensive tactic for those instances when your value might not be string already. One ring (str function) to rule them all!
• Don't let readability take a backseat. If explicit None checking makes more sense to you or your future reader, choose ternary or custom function approaches.
• Think about performance. While a xstr function adds clarity, sometimes, replacing an in-line operator with a function call might be a performance hit, an acceptable one though in most scenarios.