Dictionaries are simple databases for pairs of key (ID, name) and related values (data). Key can be a string or a number, but needs to be unique. Values can be a single number, string, or a complete structure (tuple, list, ...). Dictionaries have no order, stored items can be accessed via the key-identifier.
# create a new dictionary
d={}
# add values
d['Antje']=('Barcelona',1987)
d['Mike']=('Berlin',1983)
d
{'Antje': ('Barcelona', 1983), 'Mike': ('Berlin', 1987)}
# get value of key identifier '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)}
# empty the entire dictionary (remove all entries)
d.clear()
d
{}
# print all key-value pairs of a dictionary
for k, v in sorted(d.items()):
print(k, v)
# avoid overwriting duplicates of key identifier
k='Mike'
v=('Berlin',1983)
if k not in d: # add only if not in dictionary already
d[k]=v
# avoid KeyError (key not found)
# 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
# Simple list data-structure
mylist = ['Antje', 'Mike', 'Michel']