Unroll a nested dictionary into flat lists.

unroll_dict.py

"""
Unroll a nested dictionary into flat lists.

This might come in handy if you have on your hands a massive, hardcoded,
vertical- and horizontal-screen-spanning lookup map, and you would like to get
it into a tabular format, so you can, for example, load it into a relational
database table.
"""
import sys
import csv

# Example
d = {'a':
        {'c':
            {'e': 1,
             'f': 2},
         'd':
            {'e': 3,
             'f': 4},
        },
     'b':
        {'c':
            {'e': 5,
             'f': 6},
         'd':
            {'e': 7,
             'f': 8},
        }
    }

def unroll_dict(dict_):
    ret = []
    for k, v in dict_.iteritems():
        # Recursive case, value is another dict
        if isinstance(v, dict):
            unrolled = unroll_dict(v)
            for u in unrolled:
                ret.append([k] + u)
        # Base case, value is not dict
        else:
            ret.append([k, v])
    return ret

unrolled = unroll_dict(d)

writer = csv.writer(sys.stdout, delimiter='\t')
for row in unrolled:
    writer.writerow(row)

# Prints:
"""
a	c	e	1
a	c	f	2
a	d	e	3
a	d	f	4
b	c	e	5
b	c	f	6
b	d	e	7
b	d	f	8
"""

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