<div dir="ltr"><div class="gmail_default" style="font-family:verdana,sans-serif;font-size:small;color:#000000">New Python versions already use backwards incompatible syntax, but it has to be a strict superset so the new parser still parses old code. If a new Python version introduced syntax that would break old code, it would still work, so long as the parser knew which syntax the file contained, and was able to parse both versions.</div><div class="gmail_default" style="font-family:verdana,sans-serif;font-size:small;color:#000000"><br></div><div class="gmail_default" style="font-family:verdana,sans-serif;font-size:small;color:#000000">I personally think Python 3 should have always had a new file extension (mainly to help editors disambiguate), but some kind of directive at the top of the file would work as well, a bit like JavaScript's Strict Mode.</div><div class="gmail_default" style="font-family:verdana,sans-serif;font-size:small;color:#000000"><br></div><div class="gmail_default" style="font-family:verdana,sans-serif;font-size:small;color:#000000">The killer objection is that you have to maintain two parsers or some kind of mashup, but still, <span style="color:rgb(0,0,0);font-family:verdana,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">the old syntax would be frozen, </span>there could be a lot of reuse in the front end, and there would still only be one VM.</div><div class="gmail_default" style="font-family:verdana,sans-serif;font-size:small;color:#000000"><br></div><div class="gmail_default" style="font-family:verdana,sans-serif;font-size:small;color:#000000">I'm not hoping this happens any time soon, but if was a choice between devs maintaining two parsers or users migrating to Python 4, as a user...</div><div class="gmail_default" style="font-family:verdana,sans-serif;font-size:small;color:#000000"><br></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><span style="color:rgb(115,115,115);font-style:italic;line-height:18px"><font size="1" face="monospace, monospace">-- Carl Smith</font></span><br></div></div><div><span style="color:rgb(115,115,115);font-style:italic;line-height:18px"><font size="1" face="monospace, monospace"><a href="mailto:carl.input@gmail.com" target="_blank">carl.input@gmail.com</a></font></span></div></div></div></div></div></div>
<br><div class="gmail_quote">On 14 May 2018 at 02:28, Greg Ewing <span dir="ltr"><<a href="mailto:greg.ewing@canterbury.ac.nz" target="_blank">greg.ewing@canterbury.ac.nz</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Rob Cliffe via Python-ideas wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
  def and(x, y):<br>
    return ...<br>
<br>
#  and(1,2)      # Oops, SyntaxError. Oh, I know:<br>
  globals()['and'](1,2)  # Works!<br>
</blockquote>
<br>
If the rule I proposed for "import" were extended to "def"<br>
then and(1,2) would work. The usual way of using "and" would<br>
no longer work in that module, but this just goes to show<br>
that redefining "and" is a silly thing to do in the first<br>
place.<br>
<br>
Redefining the existing keywords could perhaps be forbidden<br>
if you really want to protect people from shooting themselves<br>
in the kidneys this particular way.<div class="HOEnZb"><div class="h5"><br>
<br>
-- <br>
Greg<br>
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