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The dictionary is similar to lists in the sense that it is also a collection of dataitems just like lists but it is different form lists in the sense that lists are sequential collections and dictionaries are non-sequential collections. In lists, where there is an order associated with the data items because they act as storage units for other objects or variables created. Dictionaries are different from lists and tuples because the group of objects they hold are not in any particular order, but rather each object has its own unique name, commonly known as a key.  

customer=dict( ) 

n=input(” Enter total number of customers”) 

i=l 

while i<=n: 

a=raw_input(“enter customer name”) 

b=raw_input(“enter customer number”) 

customer[a]=b 

i=i+l 

name=raw_input(” enter customer name to delete”) 

del customer[name] 

l=customer.keys( ) 

print “Customer Information” 

print “Name”/\t’/’number” 

for i in 1: 

print i/\t’,customer[i]

Output :

Enter total number of customers 5 

enter customer name Rohan 

enter customer number 123678 

enter customer name Ranjish 

enter customer number 123677 

enter customer name Suraj 

enter customer number 123899 

enter customer name Damu 

enter customer number 123777 

enter customer name Dhariya 

enter customer number .123885 

enter customer name to delete Suraj 

Customer Information 

Name number 

Rohan 123678 

Dhariya 123885

Ranjish 123677 

Damu 123777

Description 

The method cmp( ) compares two dictionaries based on key and values.

 Syntax 

Following is the syntax for cmp( ) method : 

cmp(dict1, dict2)

Parameters

dict1 – This is the first dictionary to be compared with dict2. 

dict2 – This is the second dictionary to be compared with dict1.

Return value :

This method returns 10 if both dictionaries are equal, – 1 if dictl < dict2 and 1 if dictl > dict2. 

Example :

The following example shows the usage of comp( ) method. 

# !/user/bin/python

dict1 = {‘Name’ : ‘Zara’, ‘Age’ : 7}; 

dict2 = {‘Name1 : ‘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 (dictl, dict4)

Let us compile and run the above program, this will produce the following result : 

Return Value : – 1 . 

Return Value : 1 

Return Value : 0

Description 

The method str( ) produces a printable string representation of a dictionary. 

Syntax 

Following is the syntax for str( ) method : 

str(dict) 

Parameters

diet – This is the dictionary.

Return Value 

This method returns string representation. 

Example : 

The following examples shows the usage of str() method.

# !/user/bin/python 

diet = {‘Name’ :’Zara’, ‘Age’ : 7); 

print “Equivalent String : %s” %str (dict) 

Let us compile and run the above program, this will produce the following result : 

Equivalent String : {‘Age’ : 7, ‘Name’ : ‘Zara’}

city=dict( ) 

n=5 

i=l while i<=n: 

a=raw_input(” enter city name”) 

b=raw_input(“enter population”) 

city[a] =b 

i=i+l print 

city 

Output :

enter city name Chennai 

enter population 3400000 

enter city name Mumbai 

enter population 8900000 

enter city name Bangalore 

enter population 98700 

enter city name Calicut 

enter population 560000 

enter city name Hyderabad 

enter population 900000

{‘Bangalore’: ‘ 98700’/ Hyderabad’: ‘ 900000’, ‘ Chennai’: ‘ 3400000’, ‘ Mumbai’: ‘ 8900000’, ‘ Calicut’: ‘ 560000’}

class xi = diet ( ) 

n = input (“Enter total number of section in xi class”) 

i = 1 while i < = n :

a = raw_input (“enter section”) 

b = raw input (“enter class teacher name”) 

classxi[a] = b i = i + 1 

print “Class”, “\t”, “Section”, 

\t„, “Teacher Name” 

for i in classxi : 

print “XI”, “\t”, i, “\t”, class xi[i] 

c=dict() 

n=input(“Enter total number” ) 

i=l 

while i<=n: 

a=raw_input(“enter place”) 

b=raw_input(“enter number”) 

c[a]=b 

i=i+l 

print “place”,”\t”/”number” 

for i in c: 

print i.”\t”.c[il

phonebook=dict( ) 

n=input(” Enter total number of friends to create a telephone book”) 

i=l 

while i<=n: 

a=raw_input(“enter name”)

b=raw_input(“enter phone number”) 

phonebook[a]=b 

i=i+l 

name=raw_input(“enter friend’s name to search for”) 

f=0

l=phonebook.keys( ) 

for i in l: 

if(cmp(i,name) == 0): 

print “Phone number= “,phonebook[i] 

f=l 

if (f==0): 

print “Given name not exist” 

Output: 

Enter total number of friends to create a telephone book 5 

enter name Ramu 

enter phone number  9842311111 

enter name Raju

enter phone number 9842309564 

enter name Sarita 

enter phone number 9842398765 

enter name Sowmya 

enter phone number 9842399922 

enter name Karan 

enter phone number 9842366554 

enter friend’s name to search for Sarita 

Phone number = 9842398765 

phonebook = dict( ) 

n = input (“Enter total number of friends”) 

i = 1 

while i<=n : 

a = raw_input (“Enter name”) 

b = raw_input (“Enter phone number”) 

phonebook [a] = b

i = i + 1 

name = raw_input (“Enter name”) 

f = 0 

l = phonebook.keys( ) 

for i in l : 

if (comp (i, name) = = 0) : 

print “Phone number =”, phonebook[i] 

f = 1 

if (f = = 0): 

print “Given name not exist”

Dictionaries can be much more useful than lists. For example : suppose we wanted to store all our friend’s cell phone numbers. We could create a list of pairs (phone number, name), but once this list becomes long enough searching this list for a specific phone number will get time consuming. Better would be if we could index the list by our friend’s name. This is precisely what a dictionary does.

Employees = {‘Rohan’ : {‘age’ : 20, ‘salary’ : 10000}, ‘Mohan’ : {‘age’ : 30, ‘salary’ : 15000}} 

for key in Employees : 

print “Employee”, key + ‘:’ 

print ‘Age :’ + str (Employees [key] [‘age’] 

print ‘Salary :’ + str (Employees [key] [‘salary’])

A dictionary is a mapping between a set of indices (which are called keys) and a set of values. Each key maps a value. The association of a key and a value is called a key-value pair.

The 3 main characteristics of a dictionary are :

1. Dictionaries are Unordered : The dictionary elements (key-value pairs) are not in ordered form.

2. Dictionary Keys are Case Sensitive : The same key name but with different case are treated as different keys in Python dictionaries. 

3. No duplicate key is allowed : When duplicate keys encountered during assignment, the last assignment wins. 

4. Keys must be immutable : We can use strings, numbers or tuples as dictionary keys but something like [‘key’] is not allowed.

dict.fromkeys( ) 

The method fromkeys( ) creates a new dictionary with keys from seq and values set to value. 

Syntax 

Following is the syntax for fromkeys( ) method : 

dict.fromkeys{seq[,value])} 

Parameters :

seq – This is the list of values which would be used be used for dictionary keys preparation.

value – This is optional, if provided then value would be set to this value. Return Value

This method returns the list. 

Example : 

The following example shows the usage of fromkeys( ) method. 

#!/user/bin/python

seq = {‘name’, ‘age’, ’sex’) 

diet = dict.from keys(seq) 

print “New Dictionary : %s” % str(dict) 

dict = dict.from keys(seq, 10) 

print “New Dictionary : %s” % str(dict) 

Let us compile and run the above program, this will produce the following result : 

New Dictionary : {‘age’ : None, ‘name’ : None, ‘sex’: None} 

New Dictionary : {‘age’ : 10, ‘name’ : 10, ‘sex’ : 10}