How do you count the number of entries in a dictionary in Python?

Counting the number of entries in a Python dictionary is straightforward because dictionaries are built‑in data structures that keep track of their keys. The simplest way is to use the built‑in len() function: len(my_dict). This returns the number of key/value pairs, i.e., the number of entries. If you need to count only keys that satisfy a condition, you can use a generator expression: sum(1 for k in my_dict if condition(k)). For counting occurrences of a particular value, iterate over my_dict.values() and compare each value. Example: target = 5; count = sum(1 for v in my_dict.values() if v == target). All these operations run in O(n) time, where n is the number of keys, because Python dictionaries are hash tables and lookups are constant time on average. Using len() is the most efficient and idiomatic approach for a simple count. If you need to count the number of keys that map to a specific value, you can use collections.Counter on the values: from collections import Counter; counter = Counter(my_dict.values()); count = counter[target]. This also runs in O(n). For very large dictionaries, you might want to avoid creating intermediate lists; generator expressions are memory efficient. In summary, len(my_dict) gives the total number of entries; for conditional counts, use generator expressions or Counter. All operations are O(n) and use constant extra space aside from the dictionary itself.