#27 Python Programming - Mathematical Functions & List P03

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Mathematical functions

Python supports a wide variety of mathematical functions.

Function	Returns	Example
abs(x)	Returns the absolute value of x	x = -35;x = abs(x) print(x)
cmp(x,y)	Returns -1 if x < y> Returns 0 if x equals to y Returns 1 if x > y.	x = 6; y = 4 print( cmp(x,y) )
exp(x)	Returns the exponential of x	import math x = 6; print( math.exp(x) )
log(x)	The natural logarithm of x	import math x = 6; print( math.log(x) )
log10(x)	The base-10 logarithm of x	import math x = 6; print( math.log10(x) )
pow(x,y)	The result of x**y	import math x = 6; print( math.pow(x,2) )
sqrt(x)	The square root of x	import math x = 6; print( math.sqrt(x) )

List

Python List is a collection of data like array in Perl, shell script & ruby
Here data are not strictly of same type. It’s not like C – array
Data in side list are ordered elements (index based)
List are mutable i.e., we can modify the content of the list
Lists have methods that allow you to manipulate the values inside them.
Python list elements are separated by comma
List elements are enclosed by square brackets [ ]

How to create a list?

Syntax:-

listname= [data1, data2, data3, data4,data5….dataN ]

db=[ “oracle” , “sql”,”mysql”,”DB2”,”sqlite”]

|__ list name

[“oracle” , “sql” ,”mysql”,”DB2”,”sqlite” ]

0 1 2 3 4 index

# List index starts at 0

To determine list type using type function

>>>  db=[ “oracle” , “sql”,”mysql”,”DB2”,”sqlite”]
>>> type(db)

Accessing list values

=> List of elements accessed using the list name

>>>print db   
#output
[ “oracle” , “sql”,”mysql”,”DB2”,”sqlite”]

Access single data from list

Syntax:-

listname [index number ]

Example:-

# print 0^th index data

>>>print db[0]
#output
'oracle'
# print 1st index data
>>>print db[1]
'sql'

5	-4	-3	-2	-1	Index From Right to Left
[‘Oracle’,	‘sql’,	‘mysql’,	‘DB2’,	‘sqlite’]
0	1	2	3	4	Index from Left to Right

Slice Operator

db=[ “oracle” , “sql”,”mysql”,”DB2”,”sqlite”]
print db[1:3]  #output [ ‘sql’,  ‘ mysql’ ]
print db[2:]    #output  [‘mysql’,’db2’,’sqllite’ ]
print db[:2]   #output   [‘oracle',’sql`]

Create employee list

>>>emp=[ ‘E123’, ‘Mr.Visa’, ‘sales’,’10.20.30.40.50’,’12995.46’ ]
>>>print emp
[ ‘E123’, ‘Mr.Visa’, ‘sales’,’10.20.30.40.50’,’12995.46’ ]
>>>print  “Hello ”,emp [1]
Hello  Mr.Visa
>>>print  emp[1] ,” working department is: ”,emp[2]
 # Mr.Visa working department is sales

Update list values

# Modify sales department in to PRODUCTION

# we can modify list values through index

Syntax :-

listname[index]= “updated value”

>>>emp[2]=”PRODUCTION”  
>>>print   emp[1] ,”Current working department is:”,emp[2]
Mr.Visa Current working department is PRODUCTION

Find the size of list

Use len() function to display the total number of elements in the list.

>>>a1=[ 10,20,’data’,’/etc/passwd’,’10.20.30.40’ ]
>>>print  len(a1)  
5

Re-cap len() we used in string to count the number of characters

>>>print  len(“Ab”)
2

Delete List Elements

To remove a list element, you can use the del() function

Syntax:- del(listname)

Example:-

>>>a1=[ 10,20,’data’,’/etc/passwd’,’10.20.30.40’ ]
>>>print  a1
[ 10,20,’data’,’/etc/passwd’,’10.20.30.40’ ]
>>>print len(a1)
 5
>>>del(a1) # delete a list name
>>>a2= [ ‘data1’,’data2’,’data3’ ]
           #    0th         1st         2nd    index
>>>print  “Total no.of elements :”, len(a2)  
Total no.of elements: 3
>>>del(a2[1])  # delete 1st index data
>>>print  “Total no.of elements :”, len(a2)
Total no.of elements: 2

Basic List operations

List respond to the + and * operators much like strings; + Operator is used for list concatenation and * is used for list repetition operators .

>>>L1=[‘data1’,’data2’,’data3’]
>>>L2=[10, 20, 30]
>>>L1+ L2
[ ‘data1’, ’data2’, ’data3’ ,10 ,20 ,30 ]
>>>L1*3
[‘data1’,’data2’,’data3’, ‘data1’, ’data2’,’data3’, ‘data1’, ’data2’,’data3’]

Membership operators with list

>>>L1=[‘data1’,’data2’,’data3’]
>>> ‘data1’  in  L1   # test  data1 is placed in the given list (L1) 
True
>>> ‘dataX’  in  L1  # test dataX is placed in the given list( L1) 
False
>>> ‘data1’ not in L1
False
>>> ‘dataX’ not in L1  # test dataX is not placed in the given list
True

List Based Method

Syntax:- sorted(list) # displays sorted order of elements

>>>sh=[”expect”,”csh”,”tcsh”,”bash”]
>>>sorted(sh)  
bash ,csh ,expect,tcsh

Syntax:-

cmp(list1,list2) #compares corresponding elements of two lists.

list1 – This is the first list to be compared.

list2 – This is the second list to be compared.

If elements are of the same type, perform the compare and return the result.
If elements are different types, check to see if they are numbers.
If numbers, perform numeric coercion if necessary and compare.
If either element is a number, then the other element is “larger” (numbers are “smallest”).
Otherwise, types are sorted alphabetically by name.

l1=[‘a’,’b’]
l2=[‘a’,’b’]
l3=[‘A’,’b’]
cmp(l1,l2)  ==> 0
cmp(l1,l3) ==> 1
cmp(l3,l1)   ==> -1

Syntax:-

len(list) #returns the number of items in list

list – list for which number of elements is to be counted.

l1=[‘data1’,’data2’,’data3’]
print  “Total no.of elements:”,len(l1)  ==> Total no.of elements: 3

Syntax:-

max(list) #returns the elements from the list with maximum value.

L1=[10,20,330,500,25]
print max(L1) ==> 500

Syntax:-

min(list) # returns the elements from the list with minimum value.

L1=[10,20,330,500,25]
print min(L1) ==> 10

List methods

To get list of methods type help() function with argument as a list

>>> help(list)

The method append() appends a passed data into the existing list.

Syntax:-

list.append (data)

>>>sh=[‘/bin/sh’, ‘/bin/bash’,’/usr/bin/tcsh’]
>>>sh.append(‘/usr/bin/perl’)  # adding “/usr/bin/perl”  to  existing list

This method does not return any value but updates existing list.

>>> sh=[‘/bin/sh’, ‘/bin/bash’,’/usr/bin/tcsh’]

>>> sh.append(‘/usr/bin/perl’)  # adding “/usr/bin/perl”  to  existing list
>>> sh
[ ‘/bin/sh’, ‘/bin/bash’,’/usr/bin/tcsh’,’/usr/bin/perl’ ]

The method count() returns count of how many times data occurs in list.

Syntax:-

List.count(‘data’)

>>>L1=[‘unix’,’linux’,’unix’,’aix’,’linux’,’winx’]
>>>print L1.count(‘linux’)  
2
>>>print L1.count(‘winx’)
1

The method extend() appends the contents of seq to list

Syntax :-

List.extend(seq) where Seq is collection of elements

L1=[‘unix’,’linux’,’aix’]
L2=[‘data1’,’data2’]
L1.extend(L2)
print “Extended List :”, L1
Extended List :[ ‘unix’,’linux’,’aix’,’data1’,’data2’]
L3=[‘unix’,’linux’,’aix’]
print “Extend list:”, L3.extend(“ABC”)
Extend list: [‘unix’,’linux’,’aix’,’A’,’B’,’C’]

The method index() returns the lowest index in list where data appears

Syntax:-

List.index(data)

This method returns index of the found object otherwise raises an exception indicating that value does not found.

>>>L1=[‘unix’,’linux’,’aix’]
>>>print L1.index(‘linux’)
1

The method insert() inserts object data into list at offset index.

Syntax:-

List.insert(index,data)

index – This is the Index where the object obj need to be inserted.

data – This is the data to be inserted into the given list

This method does not return any value but it inserts the given element at the given index.

L1=[‘unix’,’linux’,’aix’]
L1.insert(2,”SOLARIS”)
>>> L1
[‘unix’,’linux’,’SOLARIS’,’aix’]

The method pop() removes and returns last data from the list.

Syntax:-

List.pop()
List.pop(data)
=>   This method returns the removed object from the list.
L1=[‘unix’,’linux’,’aix’,’solaris’,’winx’]
>>> L1.pop()
‘winx’
>>> L1.pop(2)
‘aix’

This method remove() does not return any value but removes the given object from the list.

Syntax:-

List.remove(data)
L1=[‘unix’,’linux’,’aix’,’solaris’,’winx’]
L1.remove(‘linux’) # remove linux element from L1 list

The method reverse() does not return any value but reverse the given object in the list.

Syntax:- List.reverse()


>>> L1=[‘unix’,’linux’,’aix’,’solaris’,’winx’]
>>> L1.reverse()
>>> L1
[‘winx’,’solaris’,’aix’,’linux’,’unix’]

The method sort() sorts objects of the list

Syntax:-

List.sort()

This method does not return any value but it changes the original list
Compare sorted() function returns the list of data in sorted order but keeps the original values unchanged

>>>L1.sort()
>>>L1
[‘aix’,’linux’,’solaris’,’unix’,’winx’]

Tuple

Python tuple is a collection of data like array in Perl, shell script, ruby
Here data are not strictly of same type. It’s not like C – array
Data in side list are ordered elements (index based) like list
Unlike List, Tuple is a sequence of immutable elements, means that tuple elements cannot be updated or modified.
Like List, tuple have methods that allow you only to perform manipulation on the values inside them.
Python tuple elements are separated by comma
Tuple elements are enclosed by parentheses

How to create a tuple?

Syntax:-

tuplename= ( data1, data2, data3, data4,data5….dataN  )
db=(  “oracle” , “sql”,”mysql”,”DB2”,”sqlite” )
|__ tuple name
>>> type(db)

Print elements of tuple

>>> print db
(“oracle” , “sql”, “mysql”, “DB2”,”sqlite”)

Accessing Single data from the Tuple

Syntax:-

Tuplename[index]

>> db=(“oracle” , “sql”, “mysql”, “DB2”,”sqlite”)
#print  1st index data from tuple
print db[1]  => like list 'sql'
print db[2:]  => from 2nd index to list of all  (‘mysql’,’DB2’,’sqlite’)

Basic Tuple operation

Syntax:-

tuplename.count (Value)

# return integer total number of occurrence of a given value.
db=(‘oracle’,’sql’,’oralce’,’mysql’)
db.count(‘oracle’)  ==>  2

Syntax:-

len(tuplename)

db=(“oracle” , “sql”, “mysql”, “DB2”,”sqlite”)
print “Total no.of DB’s :”,len(db)  
# Total no.of DB’s : 5

Removing individual tuple elements is not possible.
append () or insert() is not used in tuple.
We can’t modify single data from tuple
Like List, Tuple supports min() , max() cmp() functions.
tuple(seq) – Converts a list into tuple.
list(seq) –Converts a tuple into list

Advantages of Tuple over List

Since, tuples are quite similar to lists; both of them are used in similar situations as well.
However, there are certain advantages of implementing a tuple over a list.
Below listed are some of the main advantages
1. Since tuple are immutable, iterating through tuple is faster than with list. So there is a slight performance boost.
2. Tuples that contain immutable elements can be used as key for a dictionary. With list, this is not possible.
3. If you have data that doesn’t change, implementing it as tuple will guarantee that it remains write-protected.

Reference

https://www.python.org/

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