30 Essential Python Dictionary Tricks Every Developer Should Know

1. Create a dictionary

# Create dictionary
my_dict = {"name": "Zhang San", "age": 25, "city": "Beijing"}
print(my_dict)

Output: {'name': 'Zhang San', 'age': 25, 'city': 'Beijing'}

2. Access a value

# Access a value
print(my_dict["name"])

Output: Zhang San

3. Modify a value

# Modify a value
my_dict["age"] = 26
print(my_dict)

Output: {'name': 'Zhang San', 'age': 26, 'city': 'Beijing'}

4. Add a key‑value pair

# Add a key‑value pair
my_dict["job"] = "Programmer"
print(my_dict)

Output: {'name': 'Zhang San', 'age': 26, 'city': 'Beijing', 'job': 'Programmer'}

5. Delete a key‑value pair

# Delete a key‑value pair
del my_dict["city"]
print(my_dict)

Output: {'name': 'Zhang San', 'age': 26, 'job': 'Programmer'}

6. Get dictionary length

# Get dictionary length
print(len(my_dict))

Output: 3

7. Get all keys

# Get all keys
print(my_dict.keys())

Output: dict_keys(['name', 'age', 'job'])

8. Get all values

# Get all values
print(my_dict.values())

Output: dict_values(['Zhang San', 26, 'Programmer'])

9. Get all items

# Get all items
print(my_dict.items())

Output: dict_items([('name', 'Zhang San'), ('age', 26), ('job', 'Programmer')])

10. Iterate over items

# Iterate over items
for key, value in my_dict.items():
    print(key, value)

Output:

name Zhang San

age 26

job Programmer

11. Merge two dictionaries

# Merge two dictionaries
dict1 = {"a": 1, "b": 2}
dict2 = {"c": 3, "d": 4}
merged_dict = {**dict1, **dict2}
print(merged_dict)

Output: {'a': 1, 'b': 2, 'c': 3, 'd': 4}

12. Convert two lists to a dictionary

# Convert two lists to a dictionary
keys = ["name", "age", "city"]
values = ["Zhang San", 25, "Beijing"]
list_to_dict = dict(zip(keys, values))
print(list_to_dict)

Output: {'name': 'Zhang San', 'age': 25, 'city': 'Beijing'}

13. Dictionary comprehension – create

# Create a dictionary with comprehension
squares = {x: x**2 for x in range(1, 6)}
print(squares)

Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

14. Dictionary comprehension – filter

# Filter items where value > 25
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
filtered = {k: v for k, v in my_dict.items() if v > 25}
print(filtered)

Output: {'a': 100, 'c': 300}

15. Dictionary comprehension – transform values

# Double each value
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
updated = {k: v*2 for k, v in my_dict.items()}
print(updated)

Output: {'a': 200, 'b': 50, 'c': 600, 'd': 20}

16. Dictionary comprehension – transform keys and values

# Upper‑case keys and double values
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
transformed = {k.upper(): v*2 for k, v in my_dict.items()}
print(transformed)

Output: {'A': 200, 'B': 50, 'C': 600, 'D': 20}

17. List‑to‑dict with default values

# Provide "Unknown" for missing values
keys = ["name", "age", "city"]
values = ["Zhang San", 25]
list_to_dict = {key: values[i] if i < len(values) else "Unknown" for i, key in enumerate(keys)}
print(list_to_dict)

Output: {'name': 'Zhang San', 'age': 25, 'city': 'Unknown'}

18. Tuple‑to‑dict with default values

# Convert tuple of pairs, keep existing values
tuples = (("name", "Zhang San"), ("age", 25), ("city", "Beijing"))
tuple_to_dict = {k: v for k, v in tuples}
print(tuple_to_dict)

Output: {'name': 'Zhang San', 'age': 25, 'city': 'Beijing'}

19. Sort a dictionary by value

# Sort ascending by value
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
sorted_dict = {k: v for k, v in sorted(my_dict.items(), key=lambda item: item[1])}
print(sorted_dict)

Output: {'d': 10, 'b': 25, 'a': 100, 'c': 300}

20. Remove duplicate values

# Keep only keys whose values are unique
my_dict = {"a": 100, "b": 100, "c": 300, "d": 10}
unique = {k: v for k, v in my_dict.items() if list(my_dict.values()).count(v) == 1}
print(unique)

Output: {'c': 300, 'd': 10}

21. Check if a key exists

# Membership test
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
key = "b"
if key in my_dict:
    print(f"Key '{key}' exists")
else:
    print(f"Key '{key}' does not exist")

Output: Key 'b' exists

22. Find key with maximum value

# max() with key argument
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
max_key = max(my_dict, key=my_dict.get)
print(f"Key with max value: {max_key}")

Output: Key with max value: c

23. Find key with minimum value

# min() with key argument
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
min_key = min(my_dict, key=my_dict.get)
print(f"Key with min value: {min_key}")

Output: Key with min value: d

24. Clear a dictionary

# Remove all items
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
my_dict.clear()
print(my_dict)

Output: {}

25. Copy a dictionary

# Shallow copy
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
copy_dict = my_dict.copy()
print(copy_dict)

Output: {'a': 100, 'b': 25, 'c': 300, 'd': 10}

26. Update a dictionary

# Merge another mapping
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
updates = {"b": 30, "e": 50}
my_dict.update(updates)
print(my_dict)

Output: {'a': 100, 'b': 30, 'c': 300, 'd': 10, 'e': 50}

27. Use get() with default

# Safe retrieval
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
value = my_dict.get("b", "Key not found")
print(value)

Output: 25

28. Use setdefault() to add a key

# Insert only if missing
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
my_dict.setdefault("e", 50)
print(my_dict)

Output: {'a': 100, 'b': 25, 'c': 300, 'd': 10, 'e': 50}

29. Remove a key with pop()

# pop returns the removed value
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
removed = my_dict.pop("b", "Key not found")
print(f"Removed value: {removed}")
print(my_dict)

Output:

Removed value: 25

{'a': 100, 'c': 300, 'd': 10}

30. Remove an arbitrary item with popitem()

# popitem removes the last inserted pair (Python 3.7+)
my_dict = {"a": 100, "b": 25, "c": 300, "d": 10}
item = my_dict.popitem()
print(f"Removed item: {item}")
print(my_dict)

Output:

Removed item: ('d', 10)

{'a': 100, 'b': 25, 'c': 300}