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Newsgroups: comp.lang.python
Date: Wed, 24 Oct 2012 21:27:28 -0700 (PDT)
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Subject: Re: turn list of letters into an array of integers
From: seektime <michael.j.krause@gmail.com>
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On Tuesday, October 23, 2012 11:07:29 PM UTC-7, Chris Rebert wrote:
> On Tue, Oct 23, 2012 at 10:23 PM, seektime <michael.j.krause@gmail.com> w=
rote:
>=20
> > Here's some example code. The input is a list which is a "matrix" of le=
tters:
>=20
> >    a  b  a
>=20
> >    b  b  a
>=20
> >
>=20
> > and I'd like to turn this into a Python array:
>=20
>=20
>=20
> You mean a Python list. The datatype Python calls an `array` is very
>=20
> different and relatively uncommonly used.
>=20
> Although, confusingly, Python's lists are implemented using C arrays
>=20
> rather than linked lists.
>=20
>=20
>=20
> >   1 2 1
>=20
> >   2 2 1
>=20
> >
>=20
> > so 1 replaces a, and 2 replaces b. Here's the code I have so far:
>=20
> >
>=20
> >>>> L=3D['a b a\n','b b a\n']
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> <snip>
>=20
> >>>> seq
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> > '1 2 1\n 2 2 1\n'
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> >
>=20
> > My question is how can I turn "seq" into a python array?
>=20
>=20
>=20
> I'd say you're asking the wrong question. The better question is "Why
>=20
> wasn't the result a list in the first place?". Many transformations
>=20
> are cumbersome to express over just strings, which is why the first
>=20
> job of most programs is to parse their input into a more convenient
>=20
> structure that is suited to their main task(s).
>=20
>=20
>=20
> This (along with some other improvements) leads to a better, somewhat
>=20
> different program/algorithm:
>=20
>=20
>=20
> letter2number =3D {'a': 1, 'b': 2}
>=20
> with open("path/to/file.txt", "r") as f:
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>     result =3D [[letter2number[letter] for letter in
>=20
> line.strip().split()] for line in f]
>=20
>=20
>=20
> If it's safe to assume that the correspondence between the letters and
>=20
> numbers isn't completely arbitrary, some further improvements are also
>=20
> possible.
>=20
>=20
>=20
> Some relevant docs:
>=20
> http://docs.python.org/library/stdtypes.html#string-methods
>=20
> http://docs.python.org/tutorial/datastructures.html#list-comprehensions
>=20
>=20
>=20
> Cheers,
>=20
> Chris
>=20
>=20
>=20
> P.S.: I'm guessing you obtained `L` from file.readlines() or similar;
>=20
> it is worth noting for future reference that the readlines() method is
>=20
> considered somewhat deprecated.

Thanks to everyone lots of great comments are actionable suggestions.=20

My intension is to used the numpy/scipy packages to solve the task at hand.=
 I agree that there's no point in loading a file into a format which only n=
eeds to be converted right after loading. But I'm new to Python the f.readl=
ine(s) command, according to the 2.7.3 tutorial and manual, is pretty much =
all there is for file i/o. If, as you indicated, f.readlines() is deprecate=
d then what should I use instead? I'm using ver. 2.6 on Linux (it's a bit d=
ated, I know).