cmdrrickhun...@yaho.com wrote:
I've been trying to search through the years of Python talk to find an
answer to this, but my Googlefu is weak.
In most languages, I'll do something like this
xmlWriter.BeginElement("parent");
----xmlWriter.BeginElement("child");
----------xml.Writer.Characters("subtext");
----xmlWriter.EndElement();
xmlWriter.EndElement();
Where the dashes are indentation (since some newsgroup handlers don't
do tabs well). XML writing is just an example.
In general, I'm using indentation to show logical flow through code.
That, of course, is what Python does.
Python's choice to give semantic meaning to whitespace prevents me
from doing such things.
You, of course, also want to giving semantic meaning to whitespace, but
one that happens to be different from Python's. 'Logical control flow'
versus 'output text structure'.
> What was once reserved for logical use is now used syntactically.
False opposition.
In 90% of cases, its not needed, and whitespace
significance seems to be pretty effective. In that last 10%, however,
I've been frustrated many times.
I've been using python for a few years, and gotten around this in one
way or another, but now I want to get other who work with me to pick
up Python. All newbies to Python have trouble with the idea of
whitespace sensitivity,
Absolutely not true. Python's indentation is +/- the same as what
people routinely (but usually optionally) do when writing other
algorithmic languages, including most pseudocode. It also mimics
standard outline mode and other structured text (as you with to do).
I choose Python in part *because* it has a standard mandated indentation
scheme versus the multiple optional schemes of C programmers. Enough of
the endless C whitespace wars.
I strongly suggest that you not project *your* troubles onto others.
Let them come upon it by themselves -- or not.
but how can I convince them that "it just works better"
The tradeoff is between personal flexibility (a loss to you) and
uniformity across programs (you can read *any* Python program and
understand the meaning of the indentation). Someone who does not see
the latter as a gain perhaps should not use Python.
> when I have this construct which I want to use but can't.
Yet
Has anybody found a way to emulate this behavior?
New question: this answer has perhaps been posted before.
For your example, write a context manager 'Element'
(possible in 2.5+, but I use 3.0).
class Element():
def __init__(self, item):
self.item = item
def __enter__(self):
print('<element type="%s">' % self.item)
def __exit__(self, t,v,tb):
print('</element>')
# Then
with Element('parent'):
with Element('child'):
print("subtext")
# prints
<element type="parent">
<element type="child">
subtext
</element>
</element>
Of course, the element class(es) could be in a module with global indent
and delta, methods that add and subtract the delta as appropriate, and a
print function that prepends the current indent to get something like
<element type="parent">
<element type="child">
subtext
</element>
</element>
To me, this Python-style construct is better. You get the Element
closure written 'for free'. Less need to match indent levels, no
possibility of forgetting closures. If there are multiple container
elements with different closures, you get the right one automatically
and cannot mismatch.
I've often done it
by opening an expression for the whole thing, but there's a lot of
tasks where a single expression just isn't sufficient (such as things
with assignment).
I do not understand this without a concrete example.
PS. In my opinion the solution would be to have the option of entering
a "whitespace insensitive" mode which uses C style {} and ;.
I think the above is much better ;-).
And yes, such ideas have been discussed and rejected.
Terry Jan Reedy
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