[CM] what would be like Python dictionaries?

[Michael Mossey]

I'm thinking of moving into Lisp to continue my algorithmic composition
work.  I've been working in Python.  The Python dictionary is a very useful
construct for assembling collections of keys and values---a kind of informal
named structure.  It doesn't require me to define it ahead of time.

What would be the equivalent in Lisp?  I'm thinking either property lists or
hash tables.  Property lists seem simpler than hash tables, but are there
effecient methods for

- asking if a certain property is in the property list?

- looking up the value associated with a property?

Regards,
Mike