A python version of the s-exp bibtex entry

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In this post we explored representing a bibtex entry in lisp s-exp notation, and showed interesting things that enables. Here, I explore something similar in Python. The s-exp notation in Python is really more like tuples. It looks almost identical, except we need a lot of commas for the Python syntax. One significant difference in Python is we need to define the functions in advance because otherwise the function symbols are undefined. Similar to lisp, we can define the field functions at run-time in a loop. We have to use an eval statement, which some Pythonistas find distasteful, but it is not that different to me than what we did in lisp.

The syntax for "executing" the data structure is quite different than in lisp, because this data is not code in Python. Instead, we have to deconstruct the data, knowing that the function is the first object, and it takes the remaining arguments in the tuple.

Here is the proof of concept:

def article(bibtex_key, *args):
    "Return the bibtex formatted entry"
    return ',\n'.join(['@article{{{0}}}'.format(bibtex_key)] +[arg[0](arg[1]) for arg in args[0]] + ['}'])

fields = ("author", "title", "journal", "pages", "number", "doi", "url", "eprint", "year")

for f in fields:
    locals()[f] = eval ('lambda x: "  {0} = {{{1}}}".format("' + f + '", x)')

entry = (article, "hallenbeck-2013-effec-o2",
         (author, "Hallenbeck, Alexander P. and Kitchin, John R."),
         (title, "Effects of \ce{O_2} and \ce{SO_2} on the capture capacity of a primary-amine based polymeric \ce{CO_2} sorbent"),
         (journal, "Industrial \& Engineering Chemistry Research"),
         (pages, "10788-10794"),
         (year, 2013),
         (number, 31),
         (doi, "10.1021/ie400582a"),
         (url, "http://pubs.acs.org/doi/abs/10.1021/ie400582a"),
         (eprint, "http://pubs.acs.org/doi/pdf/10.1021/ie400582a"))


print entry[0](entry[1], entry[2:])
@article{hallenbeck-2013-effec-o2},
  author = {Hallenbeck, Alexander P. and Kitchin, John R.},
  title = {Effects of \ce{O_2} and \ce{SO_2} on the capture capacity of a primary-amine based polymeric \ce{CO_2} sorbent},
  journal = {Industrial \& Engineering Chemistry Research},
  pages = {10788-10794},
  year = {2013},
  number = {31},
  doi = {10.1021/ie400582a},
  url = {http://pubs.acs.org/doi/abs/10.1021/ie400582a},
  eprint = {http://pubs.acs.org/doi/pdf/10.1021/ie400582a},
}

We can still get specific fields out. Since we used a tuple here, it is not quite as nice as using a dictionary, but it is neither too bad, and it can be wrapped in a reasonably convenient function.

def article(bibtex_key, *args):
    "Return the bibtex formatted entry"
    return ',\n'.join(['@article{{{0}}}'.format(bibtex_key)] +[arg[0](arg[1]) for arg in args[0]] + ['}'])

fields = ("author", "title", "journal", "pages", "number", "doi", "url", "eprint", "year")

for f in fields:
    locals()[f] = eval ('lambda x: "  {0} = {{{1}}}".format("' + f + '", x)')

entry = (article, "hallenbeck-2013-effec-o2",
         (author, "Hallenbeck, Alexander P. and Kitchin, John R."),
         (title, "Effects of \ce{O_2} and \ce{SO_2} on the capture capacity of a primary-amine based polymeric \ce{CO_2} sorbent"),
         (journal, "Industrial \& Engineering Chemistry Research"),
         (pages, "10788-10794"),
         (year, 2013),
         (number, 31),
         (doi, "10.1021/ie400582a"),
         (url, "http://pubs.acs.org/doi/abs/10.1021/ie400582a"),
         (eprint, "http://pubs.acs.org/doi/pdf/10.1021/ie400582a"))


for field in entry[2:]:
    if field[0] == author:
        print field

def get_field(entry, field):
    for element in entry[2:]:
        if element[0] == field:
            return element[1]
    else:
        return None

print get_field(entry, title)
print get_field(entry, "bad")
(<function <lambda> at 0x1005975f0>, 'Hallenbeck, Alexander P. and Kitchin, John R.')
Effects of \ce{O_2} and \ce{SO_2} on the capture capacity of a primary-amine based polymeric \ce{CO_2} sorbent
None

So, it seems Python can do some things like lisp in treating functions like first-class objects that can be used as functions, or keys. I still like the lisp s-exp better, but this is an interesting idea for Python too.

Copyright (C) 2015 by John Kitchin. See the License for information about copying.

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