dict.copy() / dict() / Dict Merge

# Shallow-copies a dictionary.
new_dict = dictionary.copy()

# Creates a new dictionary from keyword arguments or an existing dictionary.
new_dict = dict(key=value, ...)
new_dict = dict(dictionary)

# Merges multiple dictionaries using the unpacking operator.
merged = {**dict1, **dict2}

# Merges two dictionaries using the | operator (Python 3.9+).
merged = dict1 | dict2

# Create a shallow copy with copy().
original = {'name': 'Alice', 'age': 30}
copied = original.copy()
copied['name'] = 'Bob'
print(original['name'])  # Prints 'Alice' — the original is unchanged.
print(copied['name'])    # Prints 'Bob'.

# Create a dictionary with dict().
d1 = dict(name='Carol', age=25)
print(d1)  # Prints {'name': 'Carol', 'age': 25}.

# Merge dictionaries using the unpacking operator.
base = {'color': 'blue', 'size': 'M'}
extra = {'size': 'L', 'weight': 60}
merged = {**base, **extra}
print(merged)  # Prints {'color': 'blue', 'size': 'L', 'weight': 60}.

# Merge with the | operator (Python 3.9+).
d2 = {'x': 1, 'y': 2}
d3 = {'y': 99, 'z': 3}
result = d2 | d3
print(result)  # Prints {'x': 1, 'y': 99, 'z': 3}.

# Merge in place with |=.
settings = {'theme': 'dark', 'lang': 'ja'}
overrides = {'lang': 'en', 'font': 'mono'}
settings |= overrides
print(settings)  # Prints {'theme': 'dark', 'lang': 'en', 'font': 'mono'}.

dict.copy() creates a shallow copy. If the values are immutable objects such as strings or numbers, modifying one copy does not affect the other. However, if a value is a mutable object such as a list or another dictionary, the reference is shared between the two copies. Use copy.deepcopy() when a deep copy is required.

There are several ways to merge dictionaries. The {**d1, **d2} syntax works from Python 3.5 onward and can merge three or more dictionaries at once. Python 3.9 and later allow the more readable d1 | d2 syntax. In either case, if a key exists in both dictionaries, the value from the later dictionary takes precedence. Be careful not to overwrite values unintentionally.

For creating dictionaries with comprehensions, see Dictionary Comprehensions.