Assignment Versus Equality
bc at freeuk.com
Sun Jun 26 06:48:30 EDT 2016
On 26/06/2016 08:36, Lawrence D’Oliveiro wrote:
> One of Python’s few mistakes was that it copied the C convention of using “=” for assignment and “==” for equality comparison.
One of C's many mistakes. Unfortunately C has been very influential.
However, why couldn't Python have used "=" both for assignment, and for
equality? Since I understand assignment ops can't appear in expressions.
> It should have copied the old convention from Algol-like languages (including Pascal), where “:=” was assignment, so “=” could keep a meaning closer to its mathematical usage.
(I think Fortran and PL/I also used "=" for assignment. Both were more
commercially successful than Algol or Pascal.)
> For consider, the C usage isn’t even consistent. What is the “not equal”
> operator? Is it the “not” operator concatenated with the “equal”
> No it’s not! It is “!” followed by “=” (assignment), of all things!
I thought "!" /was/ the logical not operator (with "~" being bitwise not).
> This fits in more with the following pattern:
> A += B <=> A = A + B
> A *= B <=> A = A * B
> in other words
> A != B
> should be equivalent to
> A = A ! B
Yes, that's an another inconsistency in C. Sometimes "<>" was used for
"not equals", or "≠" except there was limited keyboard support for that.
("/=" would have the same problem as "!=")
But again, that doesn't apply in Python as the "!=" in "A != B" can't
appear in expressions.
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