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From: Paul Rubin <no.email@nospam.invalid>
Newsgroups: comp.lang.python
Subject: Re: Undefined behaviour in C [was Re: The Cost of Dynamism]
Date: Sat, 26 Mar 2016 23:34:11 -0700
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BartC <bc@freeuk.com> writes:
>  But my suggestion was to have required a keyword in front of
> such expressions.

Should there be a keyword in front of a line containing "sqrt(x)" ?
What about "launch(missiles)" ?

The compiler can't tell which of those expressions has a side effect.
The first might be buggy code but the second is idiomatic.