import itertools


def dict_product(d, repeat=1):
    """Given a dictionary `d`, return a generator over every
    combination of its values. This is very convenient for sweeping
    over various values for the same key with multiple keys. The
    values of `d` must all be lists or tuples (or other iterable)."""
    # Set up items as (([k0, k0, ...], [v0-0, v0-1, ...]),
    # ([k1, k1, ...], [v1-0, v1-1, ...]), (...), ...) pairs
    all_items = (zip([k] * len(v), v) for k, v in d.items())
    # Produce all combinations of hparams and map to dictionaries
    return map(dict, itertools.product(*all_items, repeat=repeat))

# EXAMPLE
# =======
# Instead of writing this:
for a in [1, 2, 3]:
    for b in ['spec_a', 'spec_b']:
        for c in [int, float]:
            pass  # whatever
# We can write this:
abc = dict_product(dict(
    a=[1, 2, 3],
    b=['spec_a', 'spec_b'],
    c=[int, float],
))
# ...and do what we want here.

# The contents of abc (expanded) are:
# [{'a': 1, 'b': 'spec_a', 'c': <class 'int'>},
#  {'a': 1, 'b': 'spec_a', 'c': <class 'float'>},
#  {'a': 1, 'b': 'spec_b', 'c': <class 'int'>},
#  {'a': 1, 'b': 'spec_b', 'c': <class 'float'>},
#  {'a': 2, 'b': 'spec_a', 'c': <class 'int'>},
#  {'a': 2, 'b': 'spec_a', 'c': <class 'float'>},
#  {'a': 2, 'b': 'spec_b', 'c': <class 'int'>},
#  {'a': 2, 'b': 'spec_b', 'c': <class 'float'>},
#  {'a': 3, 'b': 'spec_a', 'c': <class 'int'>},
#  {'a': 3, 'b': 'spec_a', 'c': <class 'float'>},
#  {'a': 3, 'b': 'spec_b', 'c': <class 'int'>},
#  {'a': 3, 'b': 'spec_b', 'c': <class 'float'>}]