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Newsgroups: comp.lang.python
Date: Wed, 24 Oct 2012 05:03:52 -0700 (PDT)
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Subject: Re: turn list of letters into an array of integers
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Cc: python-list@python.org, "Michael J. Krause" <michael.j.krause@gmail.com>
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Xref: csiph.com comp.lang.python:32029

Chris Rebert=E6=96=BC 2012=E5=B9=B410=E6=9C=8824=E6=97=A5=E6=98=9F=E6=9C=9F=
=E4=B8=89UTC+8=E4=B8=8B=E5=8D=882=E6=99=8207=E5=88=8629=E7=A7=92=E5=AF=AB=
=E9=81=93=EF=BC=9A
> On Tue, Oct 23, 2012 at 10:23 PM, seektime <michael.j.krause@gmail.com> w=
rote:
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> > Here's some example code. The input is a list which is a "matrix" of le=
tters:
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> >    a  b  a
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> >    b  b  a
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> >
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> > and I'd like to turn this into a Python array:
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>=20
>=20
> You mean a Python list. The datatype Python calls an `array` is very
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> different and relatively uncommonly used.
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> Although, confusingly, Python's lists are implemented using C arrays
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> rather than linked lists.

The list in python is a list of valid python objects.
For the number crunching part, please use  arrays in numarray and scipy.=20

>=20
> >   1 2 1
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> >   2 2 1
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> >
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> > so 1 replaces a, and 2 replaces b. Here's the code I have so far:
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> >
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> >>>> L=3D['a b a\n','b b a\n']
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> <snip>
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> >>>> seq
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> > '1 2 1\n 2 2 1\n'
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> >
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> > My question is how can I turn "seq" into a python array?
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>=20
>=20
> I'd say you're asking the wrong question. The better question is "Why
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> wasn't the result a list in the first place?". Many transformations
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> are cumbersome to express over just strings, which is why the first
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> job of most programs is to parse their input into a more convenient
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> structure that is suited to their main task(s).
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>=20
>=20
> This (along with some other improvements) leads to a better, somewhat
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> different program/algorithm:
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>=20
>=20
> letter2number =3D {'a': 1, 'b': 2}
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> with open("path/to/file.txt", "r") as f:
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>     result =3D [[letter2number[letter] for letter in
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> line.strip().split()] for line in f]
>=20
>=20
>=20
> If it's safe to assume that the correspondence between the letters and
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> numbers isn't completely arbitrary, some further improvements are also
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> possible.
>=20
>=20
>=20
> Some relevant docs:
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> http://docs.python.org/library/stdtypes.html#string-methods
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> 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;
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> it is worth noting for future reference that the readlines() method is
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> considered somewhat deprecated.