On 27/06/2016 00:22, Gregory Ewing wrote:
BartC wrote:
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.
I'm not sure it's fair to call it a mistake. C was
designed for expert users, and a tradeoff was likely
made based on the observation that assignment is
used much more often than equality testing.
You mean the rationale was based on saving keystrokes?
A shame they didn't consider that when requiring parentheses around
conditionals, semicolons, /*...*/ around comments, %d format codes and
elaborate for-statements then!
But you might be right in that it was probably based on existing usage
of Fortran, PL/I and maybe even Basic. (Its predecessor 'B' used "=",
but B came through BCPL which I believe used ":="; perhaps the mistake
was in discarding that.)
However, why couldn't Python have used "=" both for assignment, and
for equality?
Because an expression on its own is a valid statement,
so
a = b
would be ambiguous as to whether it meant assigning b
to a or evaluating a == b and discarding the result.
And that would be another reason why == is needed for equality.
--
Bartc
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