Python 在循环中更新字典中的键和值

Question

I'm new to programming, so I apologize in advance for any crappy code. This example is a simplified version of my problem. I am obtaining data from two separate files, indicated here as lists (eg, filea and fileb). What I would like to do is create a single dictionary (data_dict) for which the key is an id number; here as the first element in a list (eg, 100). The value would be a list which gets appended when updated. In the first loop (filea), the id is appended to the value_list and then a data value is appended (for this example a9999) and then added to the dictionary for that key (id).

The problem that I'm having is trying to get the second loop (fileb) to append correctly. The final dictionary is just the result from the second loop (fileb) as can been seen by the b9999. I'm clearly doing something wrong with extracting the value of the key from the first loop so that I can add the second data point in the second loop. The final dictionary I am trying to achieve is {100: [100, 'a9999', 'b9999'] , 101: [100, 'a9999', 'b9999']} without the id begin appended to each list twice (eg, [100, 'a9999', 100, 'b9999'])

filea = [[100,1],[101,1]]
fileb = [[100,2],[101,2]]

def my_func():
    data_dict = {} # a dictionary to hold all data
    for file in [[filea],[fileb]]: 
        name = extra_func(file) #this is only added for the simplified example
        for lists in file: 
            for digit_list in lists:
                value_list = [] # the list that will be the value of each key in data_dict
                id = digit_list[0] #the first item in the list will be the id number
                digit_list.pop(0) #then drop the id number from the list
                data_dict[id] = id #create a key based on the id number 
                #print [data_dict.get(id)] # get the value for that key
                value_list.append(id) #append the id to the value_list
                data = 9999 #this is a placeholder for the example
                value_list.append(name + str(data)) #append the data with name (a or b) for readability
                data_dict[id] = value_list #add the value the key (id)
                #print "data_dict for ", id, data_dict,"\n"
            print "data_dict for all ids in file",name, "\n", data_dict,"\n"
    return data_dict

def extra_func(file):
    if file == [filea]: #this is only added for the simplified example
        name = 'a'
    if file == [fileb]:
        name = 'b'
    return name

data_dict = my_func()
print "final dictionary", data_dict

Answer 1

The first line in your inner loop is the start of the problem: you always begin with a fresh list. Instead, use the dict.get method to get what you want for the starting list. Then just add the new data.

    for lists in file:
        for digit_list in lists:
            # Get the existing list for this ID.
            # If none, start a new one.
            id = digit_list[0] #the first item in the list will be the id number
            value_list = data_dict.get(id, [id])

            digit_list.pop(0) #then drop the id number from the list
            data_dict[id] = id #create a key based on the id number 
            #print [data_dict.get(id)] # get the value for that key
            data = 9999 #this is a placeholder for the example
            value_list.append(name + str(data)) #append the data with name (a or b) for readability
            data_dict[id] = value_list #add the value the key (id)
            #print "data_dict for ", id, data_dict,"\n"
        print "data_dict for all ids in file",name, "\n", data_dict,"\n"