Normalize field keys (to lowercase)

[csware]

Normalize field keys (to lowercase)

[tdegeus]

Thanks!

• We should add a middleware that normalizes field names.
• We could consider a default lower-case mapping.

[Technologicat]

Maybe something like this (Works For Me™)?

import bibtexparser
from bibtexparser.library import Library
from bibtexparser.model import Block, Entry

class NormalizeFieldNames(bibtexparser.middlewares.middleware.BlockMiddleware):
    def __init__(self,
                 allow_inplace_modification: bool = True):
        super().__init__(allow_inplace_modification=allow_inplace_modification,
                         allow_parallel_execution=True)

    def transform_entry(self, entry: Entry, library: "Library") -> Union[Block, Collection[Block], None]:
        for field in entry.fields:
            field.key = field.key.lower()
        return entry

Usage example:

        library = bibtexparser.parse_file(filename,
                                          append_middleware=[NormalizeFieldNames(),
                                                             bibtexparser.middlewares.SeparateCoAuthors(),
                                                             bibtexparser.middlewares.SplitNameParts()])

[tdegeus]

That's probably alright. Would you be willing to convert it to a PR (adding a test)? I think this is a quite common use-case that we should support.

[MiWeiss]

Fully agree with @tdegeus, and would appreciate a PR by @Technologicat

Just one remark: We'd have to be able to handle "new" duplicates somehow (i.e., if two field keys exist in the original block which only differ in their capitalization). That's particularly important now that we're pushing the use of entries as dicts. In principle, we have an entry type DuplicateFieldKeyBlock that should be used here, but I am also happy to support additional suggestions. These would probably have to be enabled with a corresponding constructor parameter (e.g. raising an exception). Does this make sense?

[Technologicat]

@tdegeus: Sure.

@MiWeiss: Good point about conflicting keys. But I'll need a bit more information about the desired way to tackle it.

The way this approximately went is, yesterday I got a sudden need to extract some data from BibTeX in Python.

Within an hour, I had installed bibtexparser, upgraded it to 2.x, ran into this issue (since my datafiles happened to use capitalized keys), written the simplest possible field key normalizer, and posted a copy here. So it's fair to say I'm kind of new to this project :)

[csware]

A solution would be to issue a warning (similar to library.failed_blocks) and use the last key value.

[Technologicat]

@csware: Thanks. Yes, that's one possible solution, and probably the simplest one that works.

Considering alternatives, what about the DuplicateFieldKeyBlock mentioned by @MiWeiss? EDIT: Nevermind, I think I understood what you all meant now.

[Technologicat]

Implemented, using @csware's suggestion of emitting a warning and letting the last value win. Please review.