Based on patch #5140 by Juho Vepsäläinen, this commit removes the requirement to type # at the start when you want to use Python expression evaluation when typing a value in a button.
In a nutshell, that means you can now type 3 + 5 in a numbut and see it change to 8.
Word of warning: The normal Python operator logic applies, so if you type in 1 / 3, you'll get 0 and not 0.333. There's no going around that.
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