Data structures‎ > ‎

Dictionary

Dictionaries are simple databases for pairs of a key-word and corresponding items. Key can be a string or a number, but needs to be unique. Items can be a single value or complete structure (tuple, list, ...). Dictionaries have no order, stored items can be accessed via the key-word.

# create a new dictionary
>>> d={}

# add values
>>> d['Antje']=('Barcelona',1987)
>>> d['Mike']=('Berlin',1983)
>>> d
{'Antje': ('Barcelona', 1983), 'Mike': ('Berlin', 1987)}

# get value to key-word 'Mike'
>>> d['Mike']
('Berlin', 1987)


# get all keys
sorted(d.keys())
['Antje', 'Mike']

# get all values
sorted(d.values())
[('Barcelona', 1987), ('Berlin', 1983)]


# get size of dictionary (number of entries)
>>> len(d)
2

# remove a selected entry
>>> del d['Antje']
>>> d
{'Mike': ('Berlin', 1987)}


# print all key-value pairs of a dictionary
for k, v in sorted(d.items()):
    print(k, v)

# avoid overwriting duplicate key-words
k='Mike'
v=('Berlin',1983)
if k not in d:    # add only if not in dictionary already
    d[k]=v


# get default string 'unknown' if key not in dictionary
>>> name = 'Mike'

>>> d.get('Mike', 'unknown')
('Berlin', 1983)

>>> d.get('Michael', 'unknown')
'unknown'


# Multi-key combination
d['Antje']['year']='1987'


see also:  Lists


Subpages (2): get keys Multiple keys