How can you efficiently prune a dictionary based on a custom condition?

Pruning a Dictionary Based on a Custom Condition

When working with dictionaries, it is often useful to refine their contents based on specified criteria. Suppose you have a dictionary of points represented as tuples, and you're interested in extracting only points where both the x and y coordinates are less than 5.

Traditionally, one approach involves iterating over the dictionary items using a list comprehension:

points_small = {}
for item in [i for i in points.items() if i[1][0] < 5 and i[1][1] < 5]:
    points_small[item[0]] = item[1]

While this method is functional, there is a more succinct solution using a dictionary comprehension:

points_small = {k: v for k, v in points.items() if v[0] < 5 and v[1] < 5}

This concise expression generates a new dictionary where keys and values satisfy the specified condition. Similarly, in Python 2.7 and above, the following syntax can be used:

points_small = {k: v for k, v in points.iteritems() if v[0] < 5 and v[1] < 5}

By employing dictionary comprehensions, you gain an elegant and efficient means to filter dictionaries based on arbitrary conditions, providing a more streamlined approach to data manipulation.

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