configuration files - Python's ConfigParser unique keys per section

Question

I read the part of the docs and saw that the ConfigParser returns a list of key/value pairs for the options within a section. I figured that keys did not need to be unique within a section, otherwise the parser would just return a mapping. I designed my config file schema around this assumption, then sadly realized that this is not the case:

>>> from ConfigParser import ConfigParser
>>> from StringIO import StringIO
>>> fh = StringIO("""
... [Some Section]
... spam: eggs
... spam: ham
... """)
>>> parser = ConfigParser()
>>> parser.readfp(fh)
>>> print parser.items('Some Section')
[('spam', 'ham')]

Then I went back and found the part of the docs that I should have read:

Sections are normally stored in a builtin dictionary. An alternative dictionary type can be passed to the ConfigParser constructor. For example, if a dictionary type is passed that sorts its keys, the sections will be sorted on write-back, as will be the keys within each section.

To keep my existing configuration file scheme (which I really like now ;) I'm thinking of passing a mapping-like object as mentioned above that accumulates values instead of clobbering them. Is there a simpler way to prevent key/value collapse that I'm missing? Instead of making a crazy adapter (that could break if ConfigParser's implementation changes) should I just write a variant of the ConfigParser itself?

I feel like this may be one of those 'duh' moments where I'm only seeing the difficult solutions.

[Edit:] Here's a more precise example of how I'd like to use the same key multiple times:

[Ignored Paths]
ignore-extension: .swp
ignore-filename: tags
ignore-directory: bin

I dislike the comma-delimited-list syntax because it's hard on the eyes when you scale it to many values; for example, a comma delimited list of fifty extensions would not be particularly readable.

Answer 1

ConfigParser isn't designed to handle such conditions. Furthermore, your config file doesn't make sense to me.

ConfigParser gives you a dict-like structure for each section, so when you call parser.items(section), I'm expecting similar output to dict.items(), which is just a list of key/value tuples. I would never expect to see something like:

[('spam', 'eggs'), ('spam', 'ham')]

Not to mention, how would you expect the following to behave?:

parser.get('Some Section', 'spam')

Which is the intended way to retrieve values.

If you want to store multiple values for the same key, I would suggest something like this in your config file:

[Some Section]
spam: eggs, ham

And this in your code:

spam_values = [v.strip() for v in parser.get('Some Section', 'spam').split(',')]

Of course, this will only work for values that don't contain commas themselves or handle quoting. For that, you should employ a more advanced technique (see this and this).

EDIT: If you don't mind the extra dependency, You could check out ConfigObj, which natively supports lists as a value type.