There is no logic to it. When we started coding programming languages, "=" was in the character set and it was used for assignment. It started with Fortran and earlier efforts at programming languages. Since Fortran didn't have relational operators in the first version, there was no problem. In later versions, .EQ. was used for the relational operator, allowing Fortran to remain expressible in the original 48-character set. When there were relational operators and they needed to be different, the conventions of ":=" and "=" (Algol family) and "=" and "==" (the Ratfor family) arose. The use of := (and =:) to indicate a composed arrow just didn't set well with some people. I've always liked it myself. There may be some odd connection with ":" not being available in all character sets at the time these practices were being worked out. In some languages where there is no possible confusion of assignment and the equality relational operator, "=" is used both ways. It is arbitrary. Simply arbitrary. Both operations are needed, and their symbols usually need to be distinct. That's the whole deal. Basically, "==" is now the prevailing custom for the equality relational operator in programming languages. Since mathematics doesn't have an assignment operator, and mathematicians are willing to use other symbols (e.g., arrows) when needed, we are stuck with this odd cross-over dissonance. Math teachers here can tell us whether "==" is creeping into their discipline, and how students adjust to the different senses of "=" in school. -- Dennis -----Original Message----- From: edu-sig-admin@python.org [mailto:edu-sig-admin@python.org]On Behalf Of Josh McKenzie Sent: Sunday, April 07, 2002 10:04 To: edu-sig@python.org Subject: [Edu-sig] Equality and Assignment Notation Hi Why does Python use the equal sign (=) to mean assignment, and use two equal signs (==) to mean equality? Equality and assignment are not the same, yet the meaning of the equal sign is universally understood, so why redefine its meaning? I know other languages like Java and C++ employ this convention too, but how does one explain the logic behind this approach? I'll readily admit to a bias: when I see the notation ':=' in languages like Pascal, Smalltalk or Eiffel etc, I can at least understand the distinction these languages attempt to impart to the user that equality and assignment are similar, but distinct concepts. It may seem a trivial point to bring up, but while I can explain the difference between equality and assignment, I cannot explain the logic of using the '=' and '==' notation. Thanks :-) Regards - Josh M. _________________________________________________________________ MSN Photos is the easiest way to share and print your photos: http://photos.msn.com/support/worldwide.aspx _______________________________________________ Edu-sig mailing list Edu-sig@python.org http://mail.python.org/mailman/listinfo/edu-sig