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Python function to return key for largest list in Python.
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Here is a Python function to return the largest list in Python

import collections

def _get_largest_list_key(list_of_lists):
    """Return the key for the largest list in ``list_of_lists``.

    """
    max_len = 0
    max_key = None
    for key, value in list(list_of_lists.items()):
        if len(value) > max_len:
            max_len = len(value)
            max_key = key
    return max_key

# Enter the list of lists
list_of_lists = {"a": [1, 2, 3], "b": [4, 5, 6], "c": [7, 8, 9]}

# Calling the function
print((_get_largest_list_key(list_of_lists)))

#Example Output
# a

#Remember to inspect code for bugs.