Add 100 to all values in nested dictionary
If you're using both keys and values from a dictionary, then using the items method:

... for key, val in dct.items() ...


is neater than iterating over the keys and including dct[key] everywhere. In Python 2.7+, you can use a dictionary comprehension (see e.g. the tutorial) rather than pass a list comprehension to dict:

dict_data = {key: {key_: val_+100 for key_, val_ in val.items()} 
             for key, val in dict_data.items()}


Note that using key, val and the _ versions also makes it clearer what's happening than x and y.