all Python 3Dictionaries (dict)construct

Access d[key]

access

d[key] returns the value for a key or raises KeyError if absent. To avoid the error on a missing key, use dict.get() with a default.

Syntax

d[key]

Reading and writing through square brackets are not symmetric: d[key] = 1 happily creates a missing key, while reading that same key raises KeyError. Key lookup is O(1) on average, so an in check before access costs almost nothing; but when the key is normally present, it is cheaper to read and catch KeyError instead. Note too that d.get(key) returns None both for a missing key and for a key whose value is None — only in, or your own sentinel as the default, tells those apart.

Examples

d = {'a': 1, 'b': 2}
print(d['a'])         # → 1
print('z' in d)       # → False (проверка перед d[key])

See also

Common errors

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