51 lines
1.6 KiB
Plaintext
51 lines
1.6 KiB
Plaintext
From: aa8vb at vislab.epa.gov (Randall Hopper)
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Date: Fri, 23 Apr 1999 12:37:14 GMT
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Subject: Pointers to variables
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In-Reply-To: <021801be8d86$0d3ba7a0$f29b12c2@pythonware.com>; from Fredrik Lundh on Fri, Apr 23, 1999 at 02:37:27PM +0200
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References: <19990422121403.A279051@vislab.epa.gov> <wkk8v4ef5e.fsf@turangalila.harmonixmusic.com> <19990423080721.A344578@vislab.epa.gov> <021801be8d86$0d3ba7a0$f29b12c2@pythonware.com>
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Message-ID: <19990423083714.A321566@vislab.epa.gov>
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Content-Length: 1074
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X-UID: 330
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Fredrik Lundh:
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|> but this one doesn't:
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|>
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|> (3) min = 0
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|> max = 0
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|> for ( var, val ) in [( min, 1 ), ( max, 100 )]:
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|> var = val
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|here, you tell python to change the binding for the name "var"
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|in the local name space so it points to the same thing as the
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|name "val".
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Ahh (light bulb goes on). Makes sense. I should have seen that (need my
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morning caffeine).
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When the "for" iterates, var is really an alias for min and max's storage
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-- what you want. But the problem is you can't "change" the value of
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storage with assignment to var (that just rebinds var).
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And Python being "pointerless" there is no:
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*var = val
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or:
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memcpy( var, val, sizeof(*var) )
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-like construct. So you have to resort to other means (setattr).
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|> So basically this is just a little asymmetry in the language. Putting a
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|> variable in a list/tuple (valueof(var)) performs a shallow copy rather than
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|> a deep copy.
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|nope. content is never copied. only references. all the time.
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|perfect symmetry.
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Thanks.
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Randall
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