[2, 4, 6]a = [(1, 2), (3, 4), (5, 6)]
field[a, 2]
Although it's trivial to program, I wondered whether
there was a builtin or particularly concise way to
express this idea:
[2, 4, 6]a = [(1, 2), (3, 4), (5, 6)]
field[a, 2]
where field() is some made up function.
(2, 4, 6)a= [(1, 2), (3, 4), (5, 6)]
zip(*a) [(1, 3, 5), (2, 4, 6)]
zip(*a)[1]
Unknown said:Although it's trivial to program, I wondered whether
there was a builtin or particularly concise way to
express this idea:
[2, 4, 6]a = [(1, 2), (3, 4), (5, 6)]
field[a, 2]
where field() is some made up function.
The above example is a great application for numpy's array
type:
http://numpy.scipy.org/
Here's an example showing how you extract a column using
indexing operations:
http://www.scipy.org/Tentative_NumPy_Tutorial#head-864862d3f2bb4c32f04260fac61eb4ef34788c4c
[I assume numpy is still the numerical/array package du jour?]
Although it's trivial to program, I wondered whether
there was a builtin or particularly concise way to
express this idea:
[2, 4, 6]a = [(1, 2), (3, 4), (5, 6)]
field[a, 2]
where field() is some made up function.
[2, 4, 6][l[1] for l in a]
Although it's trivial to program, I wondered whether
there was a builtin or particularly concise way to
express this idea:
[2, 4, 6]a = [(1, 2), (3, 4), (5, 6)]
field[a, 2]
where field() is some made up function.
Python 2.6 (r26:66714, Nov 18 2008, 21:48:52)
[GCC 4.0.1 (Apple Inc. build 5484)] on darwin
Type "help", "copyright", "credits" or "license" for more information.(2, 4, 6)a= [(1, 2), (3, 4), (5, 6)]
zip(*a) [(1, 3, 5), (2, 4, 6)]
zip(*a)[1]
Although it's trivial to program, I wondered whether
there was a builtin or particularly concise way to
express this idea:
a = [(1, 2), (3, 4), (5, 6)]
field[a, 2]
[2, 4, 6]
where field() is some made up function.
Python 2.6 (r26:66714, Nov 18 2008, 21:48:52)
[GCC 4.0.1 (Apple Inc. build 5484)] on darwin
Type "help", "copyright", "credits" or "license" for more information.(2, 4, 6)a= [(1, 2), (3, 4), (5, 6)]
zip(*a) [(1, 3, 5), (2, 4, 6)]
zip(*a)[1]
That would be what I was after. Where can I read about
this mysterious use of the '*'? It only works in the
context of the zip() function. It's hard to understand
how the interpreter handles that.
Tobiah said:(2, 4, 6)zip(*a)[1]
That would be what I was after. Where can I read about
this mysterious use of the '*'?
No, you aren't mistaken. Looking at the "*" symbol in the 2.6Bryan said:Hmmm... that's a harder question than I thought. Am I missing it, or
does Python's doc need a write-up of the extended call syntax?
regardsIt works generally, for any callable. See the doc for 'apply':
http://docs.python.org/library/functions.html#non-essential-built-in-functions
It not only works in a call, but also in function definitions. You can
call a function with the extended call syntax whether or not is defined
with * and ** arguments.
No, you aren't mistaken. Looking at the "*" symbol in the 2.6Bryan said:Hmmm... that's a harder question than I thought. Am I missing it, or
does Python's doc need a write-up of the extended call syntax?
regardsIt works generally, for any callable. See the doc for 'apply':
http://docs.python.org/library/functions.html#non-essential-built-in-functions
It not only works in a call, but also in function definitions. You can
call a function with the extended call syntax whether or not is defined
with * and ** arguments.
Steve Holden said:No, you aren't mistaken. Looking at the "*" symbol in the 2.6
documentation index it lists only two references. The first is the
language manual's explanation of its use in the def statement, the
second is a transitory reference to its use in function calls, but
that's in the tutorial where it is not likely to get much attention.
Mark said:There's a full description of it in 5.4.3 in the Language Reference, but
apparently not indexed.
Bryan Olson said:So I guess this means I can duck out of writing up a lecture on my own
understanding of Python's extended call syntax. Great.
I think I grock the extended call syntax, and when the question came
up I was surprised not to be able to find where I learned it. Mark,
where exactly does one look to see this "full description"?
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