PYTHON PROGRAMMING (2010)

Pythons dictionary

Dictionary is a container type facility that is used to save or contain various objects or data. General syntax for dictionary is as follows.

dict = {'Alice': '2341', 'Beth': '9102', 'Cecil': '3258'}

A dictionary can be created as follows.

dict1 = { 'abc': 456 };

dict2 = { 'abc': 123, 98.6: 37 };

Accessing value in dictionary

To access a data or element one has to use the square brackets and the key value.

Example

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};

print "dict['Name']: ", dict['Name'];

print "dict['Age']: ", dict['Age'];

Output

dict['Name']: Zara

dict['Age']: 7

Updating dictionary

Used to modify or add a new existing entry.

Example

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};

dict['Age'] = 8; # update existing entry

dict['School'] = "DPS School"; # Add new entry

print "dict['Age']: ", dict['Age'];

print "dict['School']: ", dict['School'].

Output

dict['Age']: 8

dict['School']: DPS School

Delete dictionary

It is used to remove the selected dictionary element or the entire data in dictionary elements.

Example

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};

del dict['Name']; # remove entry with key 'Name'

dict.clear(); # remove all entries in dict

del dict ; # delete entire dictionary

print "dict['Age']: ", dict['Age'];

print "dict['School']: ", dict['School'];

dict['Age']:

Traceback (most recent call last):

File "test.py", line 8, in <module>

print "dict['Age']: ", dict['Age'];

TypeError: 'type' object is unsubscriptable.

Built in dictionary functions and methods

· cmp(di1, di2)- This is to compares elements of both di.

· len(di)- This provide the total length of the di which would be equal to the number of items in the di.

· str(di)- This produces a printable string representation of a di (dictionary).

· type(variable)- This returns the type of a pass variable and also If pass variable is di, then it would return a di type.

Example

#!/usr/bin/python

dict1 = {'Name': 'Zara', 'Age': 7};

dict2 = {'Name': 'Mahnaz', 'Age': 27};

dict3 = {'Name': 'Abid', 'Age': 27};

dict4 = {'Name': 'Zara', 'Age': 7};

print "Return Value : %d" % cmp (dict1, dict2)

print "Return Value : %d" % cmp (dict2, dict3)

print "Return Value : %d" % cmp (dict1, dict)

Output

Return Value : -1

Return Value : 1

Return Value : 0