CODEWITHSUNDEEP
pythonlistdictionarypython-2.7
oneindelijk
oneindelijk

Reputation: 636

creating keys for a dictionary from a list containing the keys

I'm trying to build a matrix that holds several values in several levels. I'm trying to generate a dictionary build up like this:

{'routername':{'channel':{'01':<value>,'02':<value>}}}

The number of keys on the highest level may vary.

The script is generating a list of available routers and another list of available channels. I wrote a rather cumbersome function that test for a key and if it is not already there, it adds the key to the dictionary.

So, I was wondering if there isn't an easy way to create a dictionary with empty values for the keys in list 'routers'

def AddToChart(passed_seq):
    try:
        if str(passed_seq[0]) in chart_dict:
            if str(passed_seq[1]) in chart_dict[passed_seq[0]]:
                if str(passed_seq[2]) in chart_dict[passed_seq[0]][passed_seq[1]]:
                    if str(passed_seq[3]) in chart_dict[passed_seq[0]][passed_seq[1]][passed_seq[2]]:
                        chart_dict[passed_seq[0]][passed_seq[1]][passed_seq[2]][passed_seq[3]].update(err_sub_dict)

                    else:    
                        chart_dict[passed_seq[0]][passed_seq[1]][passed_seq[2]].update({passed_seq[3]:{}})
                        chart_dict[passed_seq[0]][passed_seq[1]][passed_seq[2]][passed_seq[3]].update(err_sub_dict)
                else:
                    chart_dict[passed_seq[0]][passed_seq[1]].update({passed_seq[2]:{passed_seq[3]:{}}})
                    chart_dict[passed_seq[0]][passed_seq[1]][passed_seq[2]][passed_seq[3]].update(err_sub_dict)
            else:
                chart_dict[passed_seq[0]].update({passed_seq[1]:{passed_seq[2]:{passed_seq[3]:{}}}})
                chart_dict[passed_seq[0]][passed_seq[1]][passed_seq[2]][passed_seq[3]].update(err_sub_dict)
        else:     
            chart_dict.update({passed_seq[0]:{passed_seq[1]:{passed_seq[2]:{passed_seq[3]:{}}}}})
            chart_dict[passed_seq[0]][passed_seq[1]][passed_seq[2]][passed_seq[3]].update(err_sub_dict)
    except ValueError:
        print "AddToChart: ",err_sub_dict,sys.exc_info()[1][0]   
    except:
        print sys.exc_info()
        print "AddToChart: variable not defined: "    + str(passed_seq)

Upvotes: 1

Views: 141

Answers (2)

Blckknght
Blckknght

Reputation: 104712

I suggest using a nested collections.defaultdict for chart_dict. It lets you provide a factory function to set up new values, so any key you request will always work. It's a little tricky to get such a deeply nested structure set up, but I think the following will do the right thing for your four-level structure (I'm assuming your <value> items are also dictionaries, as it seems your current code expects):

chart_dict = defaultdict(lambda:defaultdict(lambda:defaultdict(dict)))

With that in place, you should then be able to do the following without worrying about whether any of the keys previously referenced anything in the dictionary:

a, b, c = passed_seq
chart_dict[a][b][c].update(err_sub_dict)

I'd suggest doing something like the variable unpacking above too, though you should probably use better names than a, b, and c. Good variable names can turn something incomprehensible into something easy to grasp.

Upvotes: 1

Ellochka Cannibal
Ellochka Cannibal

Reputation: 1790

You should use

dict.setdefault()

See docs.

Example:

d = {}
d = d.setdefault("k","eggs")

>> d["k"]
eggs

d2 = {"k":1}
d2 = d2.setdefault("k","spam")
>> d2["k"]
1

Upvotes: 1

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