Python Sets and Dictionaries

Python Sets

Python Maps examples

A mapping object maps hashable values to arbitrary objects. Mappings are mutable objects. There is currently only one standard mapping type, the dictionary. Dictionaries consist of pairs (called items) of keys and their corresponding values. Dictionaries can be created by placing a comma-separated list of key: value pairs within curly braces Keys are unique within a dictionary while values may not be. The values of a dictionary can be of any type, but the keys must be of an immutable data type such as strings, numbers, or tuples.

Python Set Operations and methods

Python Set methods continueed

>>> SET={'new','old','list','new'}
>>> SET
set(['new', 'old', 'list'])

Lets play with set operations, it is more like school math here...

>>> s={1,2,3,4}
>>> k={3,4,5,6}
>>> len(s)
4
>>> len(k)
4
>>> 1 in s
True
>>> 1 in k
False
>>> 1 not in k
True
>>> s.issubset(k)
False
>>> t={1,2}
>>> t.issubset(s)
True
>>> u=s.union(k)
>>> u
set([1, 2, 3, 4, 5, 6])
>>> i=s.intersection(k)
>>> i
set([3, 4])
>>> t <= s
True
>>> s >= t
True
>>> s|k
set([1, 2, 3, 4, 5, 6])
>>> s&k
set([3, 4])
>>> s-t
set([3, 4])
>>> s^k
set([1, 2, 5, 6])
>>> c=s.copy()
>>> c
set([1, 2, 3, 4])
>>> x=10
>>> x+=1
>>> x
11
>>> s|=k
>>> s
set([1, 2, 3, 4, 5, 6])
>>> s&=k
>>> s
set([3, 4, 5, 6])
>>> s-=t
>>> s
set([3, 4, 5, 6])
>>> s.add(1)
>>> s
set([1, 3, 4, 5, 6])
>>> s.add(2)
>>> s
set([1, 2, 3, 4, 5, 6])
>>> s.pop()
1
>>> s.remove(5)
>>> s
set([2, 3, 4, 6])
>>> s.clear()
>>> s
set([])

The dict : a map/hash data type

Dictionaries are able store set of keys and set of value objects mapping like hashmap

Key- can be any immutable type
Value – can be any standard type or object type

You can define, lookup, view, delete, modify with key-value pairs can be assigned empty object with curly braces {} can be assigned with an elements

Dict methods and fucntions

• len( dict )
• dict.copy( )
• dict.items( )
• dict.keys( )
• dict.values( )
• dict.has_key(‘key’)
• viewitems( )
• viewkeys( )
• viewvalues( )

The builtin dictionary object from the os module, that helps sys-admins this would be the best example.

 os.environ
{'APACHE_HOME': '/bin/httpd.conf', 'SSH_CLIENT': '192.168.1.100 62905 22', 'LOGNAME': 'pavanbsd', 'USER': 'pavanbsd', 'HOME': '/home/pavanbsd', 'PATH': '/usr/lib/jvm/java-7-oracle/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/lib/jvm/java-7-oracle/bin:/usr/lib/jvm/java-7-oracle/db/bin:/usr/lib/jvm/java-7-oracle/jre/bin', 'LANG': 'en_IN', 'TERM': 'xterm', 'SHELL': '/bin/bash', 'XDG_SESSION_COOKIE': '9d869a27940b4997c1ddd3b60000071c-1423259642.573754-89677289', 'LANGUAGE': 'en_IN:en', 'SHLVL': '1', 'JAVA_HOME': '/usr/lib/jvm/java-7-oracle', 'CONFIG_JVM_ARGS': '-Djava.security.egd=file:/dev/./urandom', 'CLASSPATH': '/home/pavanbsd/Oracle/Middleware/Oracle_Home/wlserver/server/lib/weblogic.jar:/home/pavanbsd/Oracle/Middleware/Oracle_Home/wlserver/common/derby/lib/derbytools.jar:/home/pavanbsd/Oracle/Middleware/Oracle_Home/wlserver/common/derby/lib/derbynet.jar:.', 'J2SDKDIR': '/usr/lib/jvm/java-7-oracle', 'WL_HOME': '/home/pavanbsd/Oracle/Middleware/Oracle_Home/wlserver', '_': '/usr/bin/python', 'DERBY_HOME': '/home/pavanbsd/Oracle/Middleware/Oracle_Home/wlserver/common/derby', 'J2REDIR': '/usr/lib/jvm/java-7-oracle/jre', 'SSH_TTY': '/dev/pts/0', 'OLDPWD': '/home/pavanbsd', 'PWD': '/home/pavanbsd/pybin', 'MAIL': '/var/mail/pavanbsd', 'SSH_CONNECTION': '192.168.1.100 62905 192.168.1.105 22'}
>>> d['JAVA_HOME']
'/usr/lib/jvm/java-7-oracle'
>>> d['SHELL']
'/bin/bash'

Lets try something different on dict objects...
Lets create a dictionary and do experiment on all its methods and operations.

>>> d={1:'Pavan',2:'Sudheer',3:'Chakri'}
>>> d
{1: 'Pavan', 2: 'Sudheer', 3: 'Chakri'}
>>> d[1]
'Pavan'
>>> d={1:'Pavan',2:'Sudheer',3:'Chakri'}
>>> d[1]='Vybhava'
>>> d
{1: 'Vybhava', 2: 'Sudheer', 3: 'Chakri'}
>>> len(d)
3
>>> c=d.copy()
>>> c
{1: 'Vybhava', 2: 'Sudheer', 3: 'Chakri'}
>>> c[1]='Pavan'
>>> c
{1: 'Pavan', 2: 'Sudheer', 3: 'Chakri'}
>>> c.keys()
[1, 2, 3]
>>> c.values()
['Pavan', 'Sudheer', 'Chakri']
>>> c.items()
[(1, 'Pavan'), (2, 'Sudheer'), (3, 'Chakri')]
>>> c.items()[1]
(2, 'Sudheer')
>>> c.items()[2]
(3, 'Chakri')
>>> d.has_key(3)
True
>>> d.has_key(4)
False
>>> d.has_key(5)
False
>>> d.viewitems()
dict_items([(1, 'Vybhava'), (2, 'Sudheer'), (3, 'Chakri')])
>>> d.viewkeys()
dict_keys([1, 2, 3])
>>> d.viewvalues()
dict_values(['Vybhava', 'Sudheer', 'Chakri'])
>>> d.get(1)
'Vybhava'

Sample script that illustrates the Python dictionary object types.

dict = {'Language': 'Python', 'Founder': 'Guido Van Rossum'}
print dict
print "Length of dictionary : %d" %  len(dict)
copydict = dict.copy()
print "New Dictionary : %s" %  str(copydict)
print "Items in dictionary: %s" % dict.items()
print "Keys in dictionary: %s" % dict.keys()
print "Vales in Dictionary: %s" % dict.values()
print "Key in dictionary or not: %s" % dict.has_key('Language')
print "Key in dictionary or not: %s" % dict.has_key('Year')

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