<div dir="ltr"><br><br><div class="gmail_quote"><div dir="ltr">On Wed, May 30, 2018 at 11:32 AM Peter O'Connor <<a href="mailto:peter.ed.oconnor@gmail.com">peter.ed.oconnor@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> <span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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">In comparison, I think that := is much simpler.<span> </span></span></blockquote><div><br></div></div><div dir="ltr">In this case that's true, but a small modification:<div><br></div><div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> updates = {</div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> y: do_something_to(potential_update)</div></div></div><div dir="ltr"><div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> for x in need_initialization_nodes</div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> for y in [x, *x.synthetic_inputs()]</div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> if potential_update is not None</div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> given potential_update = command.create_potential_</span><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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">update(y)</span></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> }</div><br></div></div><div dir="ltr"><div></div><div>Shows the flexibility of this given syntax vs ":="</div><div><br></div><div>If we think of "given" as just inserting a line with variable-definitions before the preceding statement, it seems clear that:<br></div></div><div dir="ltr"><div><br></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> updates = {</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> y: potential_update</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"> given potential_update = command.create_potential_</span><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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">update(y)</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8px;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"><span class="m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"> for x in need_initialization_nodes<br> for y in [x, *x.synthetic_inputs()]<br></span><span class="m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"> if potential_update is not None<br> }</span><br></div><div><span class="m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"><br></span></div></div><div dir="ltr"><div><span class="m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"><span style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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">Should raise a NameError: name 'potential_update' is not defined, and</span></span></div></div><div dir="ltr"><div><span class="m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"><br></span></div><div><span class="m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;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;text-decoration-style:initial;text-decoration-color:initial;font-size:12.8px;background-color:rgb(255,255,255);float:none;display:inline"> updates = {</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;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;text-decoration-style:initial;text-decoration-color:initial;font-size:12.8px;background-color:rgb(255,255,255)"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;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;text-decoration-style:initial;text-decoration-color:initial;font-size:12.8px;background-color:rgb(255,255,255);float:none;display:inline"> y: potential_update</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;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;text-decoration-style:initial;text-decoration-color:initial;font-size:12.8px;background-color:rgb(255,255,255)"><span class="m_2428933847504204795gmail-im" style="font-family:arial,sans-serif;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;text-decoration-style:initial;text-decoration-color:initial;color:rgb(80,0,80);font-size:12.8px;background-color:rgb(255,255,255)"> for x in need_initialization_nodes<br> for y in [x, *x.synthetic_inputs()]<br style="font-family:arial,sans-serif;font-size:12.8px;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;color:rgb(34,34,34)"><span style="font-family:arial,sans-serif;font-size:12.8px;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;color:rgb(34,34,34);float:none;display:inline"> given potential_update = command.create_potential_</span><span style="font-family:arial,sans-serif;font-size:12.8px;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;color:rgb(34,34,34);float:none;display:inline">update(y)</span><br></span><span class="m_2428933847504204795gmail-im" style="font-family:arial,sans-serif;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;text-decoration-style:initial;text-decoration-color:initial;color:rgb(80,0,80);font-size:12.8px;background-color:rgb(255,255,255)"> if potential_update is not None<br> }</span><br></span></div><div><span class="m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"><br></span></div></div><div dir="ltr"><div><span class="m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"><div style="color:rgb(34,34,34);font-family:arial,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;text-decoration-style:initial;text-decoration-color:initial"><span class="m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"><span style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px;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"><br class="m_2428933847504204795gmail-Apple-interchange-newline">Should raise a NameError: name 'y' is not defined.</span></span></div></span></div></div></blockquote><div><br></div><div>The reason I want it like that for comprehensions is that I think of it as equivalent to:</div><div><br></div><div>updates = {}</div><div><span class="inbox-inbox-m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px">for x in need_initialization_nodes:<br> for y in [x, *x.synthetic_inputs()]:<br style="font-size:12.8px;color:rgb(34,34,34)"><span style="font-size:12.8px;color:rgb(34,34,34)"> potential_update = command.create_potential_</span><span style="font-size:12.8px;color:rgb(34,34,34)">update(y)</span><br></span><span class="inbox-inbox-m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px"> if potential_update is not None:<br></span></div><div><span class="inbox-inbox-m_2428933847504204795gmail-im" style="color:rgb(80,0,80);font-family:arial,sans-serif;font-size:12.8px"> updates[y] = potential_update</span></div><div><br></div><div>But you're right that this would be a second addition to the grammar. One addition would be to "test" for something like</div><div><br></div><div>test: bool_test [comp_given]<br>bool_test: or_test ['if' or_test 'else' test] | lambdef</div><div>comp_given: 'given' testlist_star_expr annassign<br></div><div><br></div><div>The second would permit the usage in comprehensions:</div><br>comp_iter: comp_for | comp_if | comp_given</div><div class="gmail_quote"><br></div><div class="gmail_quote">Best,</div><div class="gmail_quote"><br></div><div class="gmail_quote">Neil</div><div class="gmail_quote"><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><span class="m_2428933847504204795gmail-im" style="text-align:start;text-indent:0px;text-decoration-style:initial;text-decoration-color:initial"><font color="#500050" face="arial, sans-serif"><span style="font-size:12.8px;background-color:rgb(255,255,255)">For safety it seems reasonable that if a variable is "given" in a comprehension, trying to refer to it (even if it defined in the enclosing scope) before the inner-definition will result in a NameError.</span></font></span></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, May 30, 2018 at 2:22 PM, Steven D'Aprano <span dir="ltr"><<a href="mailto:steve@pearwood.info" target="_blank">steve@pearwood.info</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span>On Wed, May 30, 2018 at 02:42:21AM -0700, Neil Girdhar wrote:<br>
<br>
> With "given", I can write:<br>
> <br>
> potential_updates = {<br>
> y: potential_update<br>
> for x in need_initialization_nodes<br>
> for y in [x, *x.synthetic_inputs()]<br>
> given potential_update = command.create_potential_update(y)<br>
> if potential_update is not None}<br>
<br>
</span>I'm not sure if that would be legal for the "given" syntax. As I <br>
understand it, the "given" syntax is:<br>
<br>
expression given name = another_expression<br>
<br>
but you've got half of the comprehension stuffed in the gap between the <br>
leading expression and the "given" keyword:<br>
<br>
expression COMPREH- given name = another_expression -ENSION<br>
<br>
so I think that's going to be illegal.<br>
<br>
<br>
I think it wants to be written this way:<br>
<span><br>
potential_updates = {<br>
y: potential_update<br>
for x in need_initialization_nodes<br>
for y in [x, *x.synthetic_inputs()]<br>
</span><span> if potential_update is not None<br>
</span> given potential_update = command.create_potential_update(y)<br>
}<br>
<br>
<br>
Or maybe it should be this?<br>
<br>
potential_updates = {<br>
y: potential_update<br>
given potential_update = command.create_potential_update(y)<br>
<span> for x in need_initialization_nodes<br>
for y in [x, *x.synthetic_inputs()]<br>
</span><span> if potential_update is not None<br>
}<br>
<br>
<br>
</span>I'm damned if I know which way is correct. Either of them? Neither?<br>
<br>
In comparison, I think that := is much simpler. There's only one place <br>
it can go:<br>
<span><br>
potential_updates = {<br>
y: potential_update<br>
for x in need_initialization_nodes<br>
for y in [x, *x.synthetic_inputs()]<br>
</span> if (<br>
potential_update := command.create_potential_update(y)<br>
) is not None<br>
}<br>
<span class="m_2428933847504204795HOEnZb"><font color="#888888"><br>
<br>
-- <br>
Steve<br>
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