expression form of one-to-many dict?

[Larry Bates]

Steven,

Suggestion: It is a bad idea to name any variable
"map".  When you do, you destroy your ability to call
Python's map function. Same goes for "list", "str",
or any other built-in function.

If you haven't been bitten by this you will, I was.

Larry Bates

Steven Bethard wrote:
> So I end up writing code like this a fair bit:
> 
> map = {}
> for key, value in sequence:
>     map.setdefault(key, []).append(value)
> 
> This code basically constructs a one-to-many mapping -- each value that 
> a key occurs with is stored in the list for that key.
> 
> This code's fine, and seems pretty simple, but thanks to generator 
> expressions, I'm getting kinda spoiled. ;)  I like being able to do 
> something like the following for one-to-one mappings:
> 
>     dict(sequence)
> 
> or a more likely scenario for me:
> 
>     dict((get_key(item), get_value(item) for item in sequence)
> 
> The point here is that there's a simple sequence or GE that I can throw 
> to the dict constructor that spits out a dict with my one-to-one mapping.
> 
> Is there a similar expression form that would spit out my one-to-many 
> mapping?
> 
> Steve