merge

`dict1 |= dict2`

In-place merge operator (Python 3.9+) that updates d1 with entries from other, with other's values winning on shared keys. Unlike |, the right operand can be any iterable of pairs or a mapping — matching update()'s flexibility.

Syntax

d1 |= other

Parameters

Parameter	Purpose
left operand	Dict mutated in place
right operand	Mapping OR iterable of (key, value) pairs

Examples

>>> d = {'a': 1, 'b': 2}
>>> d |= {'b': 99, 'c': 3}
>>> d
{'a': 1, 'b': 99, 'c': 3}

Mutates d in place, right side wins

>>> d = {'a': 1}
>>> d |= [('b', 2), ('c', 3)]
>>> d
{'a': 1, 'b': 2, 'c': 3}

Accepts an iterable of pairs (unlike plain |)

>>> d = {'a': 1}
>>> ref = d
>>> d |= {'b': 2}
>>> ref
{'a': 1, 'b': 2}

In-place — aliases observe the change

>>> d = {'a': 1}
>>> d = d | {'b': 2}
>>> # equivalent RESULT to d |= ..., but rebinds instead of mutating

Contrast with |, which creates a new dict

Gotcha

Requires Python 3.9+. |= mutates in place like update() — a rebinding 'd = d | other' produces a new dict and does NOT affect other references.

Related methods

dict1 | dict2

Merge operator (Python 3.9+) that returns a new dict containing the entries of d1 followed by d2, with d2's values winning on shared keys. Both operands must be dicts; neither is mutated.

dict.update

Updates the dictionary in place with key/value pairs from other, overwriting existing keys. Accepts another mapping, an iterable of key/value pairs, and/or keyword arguments; returns None.

dict[key] = value

Assigns value to key using bracket subscription syntax, invoking __setitem__ under the hood. Creates the entry if key is absent, or overwrites the existing value; preserves the original insertion order when the key already exists.

dict.fromkeys

Class method that builds a new dict whose keys come from iterable and whose values are all set to value (default None). The same value object is shared across every key — beware mutable defaults.

dict.copy

Returns a shallow copy of the dictionary — a new dict object with the same key-value pairs. Values themselves are not copied, so nested mutable objects are still shared between the original and the copy.

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