Question

I am trying to create a dictionary from a list and tuple of tuples as illustrated below. I have to reverse map the tuples to the list and create a set of non-None column names.

Any suggestions on a pythonic way to achieve the solution (desired dictionary) is much appreciated.

MySQL table ‘StateLog’:

Name NY   TX   NJ
Amy  1    None 1
Kat  None 1    1
Leo  None None 1

Python code :

## Fetching data from MySQL table
#cursor.execute("select * from statelog")
#mydataset = cursor.fetchall()
## Fetching column names for mapping
#state_cols = [fieldname[0] for fieldname in cursor.description]

state_cols = ['Name', 'NY', 'TX', 'NJ']
mydataset = (('Amy', '1', None, '1'), ('Kat', None, '1', '1'), ('Leo', None, None, '1'))

temp = [zip(state_cols, each) for each in mydataset]

# Looks like I can't do a tuple comprehension for the following snippet : finallist = ((eachone[1], eachone[0]) for each in temp for eachone in each if eachone[1] if eachone[0] == 'Name')
for each in temp:
    for eachone in each:
        if eachone[1]:
            if eachone[0] == 'Name':
                k = eachone[1]
            print k, eachone[0]

print '''How do I get a dictionary in this format'''            
print '''name_state = {"Amy": set(["NY", "NJ"]),
                "Kat": set(["TX", "NJ"]),
                "Leo": set(["NJ"])}'''

Output so far :

Amy Name
Amy NY
Amy NJ
Kat Name
Kat TX
Kat NJ
Leo Name
Leo NJ

Desired dictionary :

name_state = {"Amy": set(["NY", "NJ"]),
              "Kat": set(["TX", "NJ"]),
              "Leo": set(["NJ"])}

Answer 1

To be really honest, I would say your problem is that your code is becoming too cumbersome. Resist the temptation of “one-lining” it and create a function. Everything will become way easier!

mydataset = (
        ('Amy', '1', None, '1'),
        ('Kat', None, '1', '1'),
        ('Leo', None, None, '1')
)

def states(cols, data):
    """
    This function receives one of the tuples with data and returns a pair
    where the first element is the name from the tuple, and the second
    element is a set with all matched states. Well, at least *I* think
    it is more readable :)
    """
    name = data[0]
    states = set(state for state, value in zip(cols, data) if value == '1')
    return name, states

pairs = (states(state_cols, data) for data in mydataset)
# Since dicts can receive an iterator which yields pairs where the first one
# will become a key and the second one will become the value, I just pass
# a list with all pairs to the dict constructor.
print dict(pairs)

The result is:

{'Amy': set(['NY', 'NJ']), 'Leo': set(['NJ']), 'Kat': set(['NJ', 'TX'])}