A Data Structure is simply a structure which holds data together. Data structures are very useful as they are used to store a collection of of related data.
Data Structures in Python
The built-in Data Structures in Python are as follows-
1.List
2.Tuple
3.Dictionary
4.Set
List
A list is an ordered collection of data items. Lists are used to group together some other values. A list can contain values of any type. The items of a list are enclosed within square brackets. Lists are mutable, whic means you can add, remove or search for items in a list. Here is how to create a simple list-
#a list of friends is created friends=[‘pervej’,’joy’,’arafat’] print “I have “,len(friends),” friends. They are-“ for i in friends: print i #add a new friend to friend list friends.append(“rakib”) #delete an enty from friend list del friends[1] print “My friend list is now”,friends
Output:
I have 3 friends. They are-
pervej
joy
arafat
My friend list is now [“pervej”,”arafat”,”rakib”]
The example above demonstrates how to create a list, add & delete item from it. To access an item from a list index numbers are used. Remember, Python starts counting items in a list from 0, means first item of a list is 0,not 1.
Note: The items of a list may be of any data type. Also a list can be nested into another list. Take a look at the following lists-
list1=[6,7,8] #list of integers list2=[6.3,9.0,6.1] #list of floating points list3=[“mango”,”apple”,”banana”] #list of strings list4=[“python”,12.7,25] #list of items of mixed data types list5=[“apple”,8,[“atik”,”pervej”]] #list within another list
Tuple
Tuples are like lists except they are immutable, which means they cann’t be modified. They are usually used in cases where the collection of items need not to be changed. The items of a tuple are seperated by comma and enclosed within a pair of parentheses.
Example:Using Tuples
#creating a tuple fruits=(“mango”,”apple”,”orange”) new_fruits=(“banana”,”berry”,fruits) print fruits[1] print new_fruits[0] print new_fruits[2][2]
Output:
apple
mango
orange
Tuples with print statement
Sometimes it is useful to use tuple along with print statement. Here is how it is done-
name=”atik” age=20 print “%s is %d years of age”%(name,age) #here (name,age) is a tuple
Output:
atik is 20 years of age
Here tuple with print statement makes it possible to avoid the usage of commas and make easy to print output. What Python does here is that it converts each item in the tuple into a string and substitutes that string value into the place of the specification.
Dictionary
Another important built-in data type in Python is dictonary. Unlike lists and tuples, dictionaries are indexed by keys whereas lists and tuples are indexed by a range of numbers. Simply a dictionary is a mapping between a set of keys and a set of values.Each key maps to a value. The association of a key-value pair is called an item. The keys are immutable.
A dictionary is defined like this: d ={key1 : value1, key2 : value2 }. The key and value pairs in a dictionary is separated by a colon, and the pairs are separated themselves by commas and all this are enclosed in a pair of curly brackets.
Take a look at the example below how to create a dictionary, add , delete and search an item-
#creating a dictionary
phone_book={“atik”:”atik.bd08@gmail.com”,
“pervej”:”ympervej@yahoo.com”,
“rakib”:”rakib07@yahoo.com”}
#add a new item
phone_book[“arafat”]=”aryan.ict08@yahoo.com”
#delete an existing item
del phone_book[“rakib”]
for i,j in phone_book.items():
print “Contact %s at %s”%(i,j)
#search for an item
if phone_book.has_key(“atik”):
print “Atik is available at %s”%”%phone_book[“atik”]
Output:
Contact atik at atik.bd08@gmail.com
Contact pervej at ympervej@yahoo.com
Contact arafat at aryan.ict08@yahoo.com
Atik is available at atik.bd08@gmail.com
Set
Newer versions of python includes a new data type named set which supports mathematical operations like union, intersection, difference and symmetric difference. A set is simply an unodered collection of elements which permits no duplicated element. So, sets are usefull in membership testing and eliminating duplicate entries.
Creating set
Sets are created using the function set() or by using curly braces. Here is how to create set-
Example:Creating set
>>>users={‘atik’,’pervej’,’rakib’,’atik’}
>>>print (users)
{‘atik’,’pervej’,’rakib’}
Here we have created a simple set named users. As i mentioned earlier, a set never permits duplicated entries. So when we print the set, we get only the unique entries. Look at the print statement, which is not similar so far we have seen. This is because at newer version of python, print() is a function and you have to print anything like this.
Set operations
We have already known that set supports mathematical operations like union, intersection, difference and symmetric difference. The following example demonstrates the mathematical operations of set-
Example:Mathematical operations of set
>>>a=set(‘abdame’)
>>>b=set(‘amtda’)
>>>a
{‘a’,’b’,’d’,’m’,’e’}
>>>b
{‘a’,’m’,’t’,’d’}
#difference of a & b
>>>a – b
{‘b’,’e’}
#union of a & b
>>>a | b
{‘a’,’b’,’d’,’m’,’e’,t’}
#intersection of a & b
>>>a & b
{‘a’,’m’,’d’}
Sequence
List, tuples and strings are example of sequences. There are two main features of sequence-
1.Indexing operation
2.Slicing operation
Indexing operation allows us to fetch a particular item in the sequence while slicing operation is useful to retrieve a slice of the sequence. The following example demonstrates these operations-
Example:Sequence operations
friends=[‘joy’,’rahat’,’rony’,’pervej’] #indexing print friends[0] print friends[1] print friends[2] print friends[3] print friends[-2] #slicing using a list print friends[1:-2] print friends[:] #slicing using a string name=”atik” print name[0:1] print name[1:4]
Output:
joy
rahat
rony
pervej
rony
rahat
[‘joy’,’rahat’,’rony’,’pervej’]
a
tik
MultiQuote
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