Dictionary

Links

Initialise

results = {}

results = {'a' : 1, 'b' : 2, 'c' : 3}

params = dict(name='Alison', post_code='EX2')

Note: See zip in Tuple…

Alternatively, use setdefault. This class method is similar to get(), but will set dict[key]=default if key is not already in dict:

In [1]: dict = {'Name': 'Zara', 'Age': 7}
In [2]: print "Value : %s" %  dict.setdefault('Age', 99)
Value : 7

In [3]: print "Value : %s" %  dict.setdefault('Colour', 'Green')
Value : Green

In [4]: dict
Out[4]: {'Age': 7, 'Colour': 'Green', 'Name': 'Zara'}

Adding

result[key] = value

Convert

Dictionary to list of tuples:

l = properties.items()

Tuple to a dictionary:

>>> t = ((0, 'Green'), (1, 'Red'))
>>> dict(t)
{0: 'Green', 1: 'Red'}

Delete

del result[key]

Also see pop below..

Get

results.get(key)

Note:

  • If you want to return a value if key does not exist use: get(key, default) - when default is not provided and key is not in the map, None is returned.

  • Also see pop below..

Exists

if 'svn:mime-type' in properties:

…in older version of python:

tel.has_key('guido')

Looping

python 3:

>>> for k, v in knights.items():

python 2:

>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.iteritems():
...     print k, v
...
gallahad the pure
robin the brave
>>> for key in knights.keys():
...     print key, knights[key]
>>> for key, value in knights.items():
...     print key, value

Note: iteritems (and xrange) only provide values when requested. items (and range) build complete list when called.

Merge

>>> family = {'Peter':44, 'Alison':45}
>>> children = {'Barry':21, 'Martin':18}
>>> family.update(children)
>>> family
{'Peter': 44, 'Alison': 45, 'Barry': 21, 'Martin': 18}

Ordered

from collections import OrderedDict
result = OrderedDict()

Pop

>>> d = {'a':1, 'b':2}
>>> d.pop('b')
2
>>> d
{'a': 1}
>>> d.pop('c')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'c'
>>> d.pop('c', None)

Sort

Sort the whole dictionary in python 3:

from collections import namedtuple, OrderedDict

def url(self, path, **kwargs):
    ordered = OrderedDict(sorted(kwargs.items()))

Sort a dictionary by the values:

import operator
sorted(descriptions.items(), key=operator.itemgetter(1))

Return the keys as a list… (and sort in place):

l = results.keys();
l.sort()

Reverse

python 2.7 and above I think:

>>> d = {'name': 'Patrick', 'distance': 23}
>>> {v: k for k, v in d.items()}
{'Patrick': 'name', 23: 'distance'}

Values

In python 3, you probably need to convert the values to a list e.g:

return list(result.values())

I don’t fully understand this yet, but perhaps Dictionary view objects might help?