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I would hazard a guess that it is because the statement allows for easily adding a `print varname` in your code while debugging.

It's two extra chars to write print(varname). One if your editor auto-inserts matching parens!

Since the space is replaced by the first paren, it's either 0 or 1 more chars :)

Shift-9 is more fiddly to type than space though :P

print(varname) is one extra keystroke -- and a whole more convenient than a statement when you want to do it in a lambda for debugging.