How to create a dict from 2 dictionaries in Python?

dictionary, python

Solution

If you use a dict as an iterator, it will yield only its keys, not tuples of keys and values. You would have to use `categories.items()` (or `categories.iteritems()` if you are only using Python 2.x) to get those tuples:

for key, val in categories.items() :
    for k, v in items.items() :
        if key == v :
            print(val, k)

You can use dict comprehensions to get a dict with category names as keys and all items in that category as values:

>>> dict3 = { catname : [ item for item, itemcat in items.items() if itemcat == cat  ] for cat, catname in categories.items()  }
>>> dict3
{'Antics': ['Picture', 'Clock'],
'Bookz': ['Thinking in C++', 'Thinking in Java'],
'Clothes': ['Asus', 'HP'],
'Computers': [],
'Gamez': ['Diablo 3', 'Diablo 2', 'Cabal', 'WoW'],
'Jewelry': ['Golden ring'],
'Moviez': ['The pianist', 'Batman', 'Spider-Man'],
'Music': [],
'Photography': [],
'Tickets': ['Ticket for Mettalica concert',
'Ticket for Placebo concert',
'Ticket for Iron Maiden concert']}

Explanation:

The inner comprehension in square brackets will list all items that have a category of `cat`. The outer comprehension will iterate over all category keys and names, setting the category name as the new dict key and the inner comprehension as a value.

Problem

I'm dealing with Python dicts now. I wrote a code: ``` import random categories = {1 : "Antics", 2 : "Tickets", 3: "Moviez", 4 : "Music", 5 : "Photography", 6 : "Gamez", 7 : "Bookz", 8 : "Jewelry", 9 : "Computers", 10 : "Clothes"} items = {"Picture" : 1, "Clock" : 1, "Ticket for Mettalica concert" : 2, "Ticket for Iron Maiden concert" : 2, "Ticket for Placebo concert" : 2, "The pianist" : 3, "Batman" : 3, "Spider-Man" : 3, "WoW" : 6, "Cabal" : 6, "Diablo 3" : 6, "Diablo 2" : 6, "Thinking in Java" : 7, "Thinking in C++" : 7, "Golden ring" : 8, "Asus" : 10, "HP" : 10, "Shoes" : 11} for key, val in categories : for k, v in items : if key == v : print(val, k) ``` I wanted to create a 3rd dict, where i would have sth like : ``` dictThe3rd = {"Antics" : "Picture", "Antics" : "Clock", "Tickets" : "Ticket for Mettalica concert", "Ticket" : "Ticket for Iron Maiden concert", "Ticket" : "Ticket for Placebo concert", ...} ``` and so go on. How to do this? My code shows: ``` test.py, line 14, in <module> for key, val in categories : TypeError: 'int' object is not iterable ```

Original source