Python Dictionary Data Structure
A Python Dictionary Data Structure is an associative array data structure that is a Python data structure (based on the Python dictionary data type).
- AKA: Associative Python Array.
- Context:
- It can range from being a Python Dictionary of Dictionaries to being a Python Dictionary of Lists.
- It can be iterated over:
for key in dict: print key, dict[key]for key in dict.iterkeys(): print key, dict[key]for key, value in dict.iteritems(): print key, value
- Example(s):
tel = dict([('sape', 49), ('guido', 27), ('jack', 98)])tel = {'jack': 98, 'sape': 49}
tel['guido'] = 27- a Python Dictionary of Dictionaries?
- a Python Dictionary of Lists?
- Counter-Example(s):
- See: Hash Key, Python Loop.
References
2013
- https://docs.python.org/2/tutorial/datastructures.html#dictionaries
- Another useful data type built into Python is the dictionary (see Mapping Types — dict). Dictionaries are sometimes found in other languages as “associative memories” or “associative arrays”. Unlike sequences, which are indexed by a range of numbers, dictionaries are indexed by keys, which can be any immutable type; strings and numbers can always be keys. Tuples can be used as keys if they contain only strings, numbers, or tuples; if a tuple contains any mutable object either directly or indirectly, it cannot be used as a key. You can’t use lists as keys, since lists can be modified in place using index assignments, slice assignments, or methods like append() and extend().
It is best to think of a dictionary as an unordered set of key: value pairs, with the requirement that the keys are unique (within one dictionary). A pair of braces creates an empty dictionary: {}. Placing a comma-separated list of key:value pairs within the braces adds initial key:value pairs to the dictionary; this is also the way dictionaries are written on output.
The main operations on a dictionary are storing a value with some key and extracting the value given the key. It is also possible to delete a key:value pair with del. If you store using a key that is already in use, the old value associated with that key is forgotten. It is an error to extract a value using a non-existent key.
The keys() method of a dictionary object returns a list of all the keys used in the dictionary, in arbitrary order (if you want it sorted, just apply the sorted() function to it). To check whether a single key is in the dictionary, use the in keyword.
- Another useful data type built into Python is the dictionary (see Mapping Types — dict). Dictionaries are sometimes found in other languages as “associative memories” or “associative arrays”. Unlike sequences, which are indexed by a range of numbers, dictionaries are indexed by keys, which can be any immutable type; strings and numbers can always be keys. Tuples can be used as keys if they contain only strings, numbers, or tuples; if a tuple contains any mutable object either directly or indirectly, it cannot be used as a key. You can’t use lists as keys, since lists can be modified in place using index assignments, slice assignments, or methods like append() and extend().