Basics of Python for Data Science

Introduction to Python

Python is an open-source, high-level and general-purpose programming language which was created by Guido Van Rossum and released in 1991. Python 3.7 was released on 27.06.2018. It is very powerful, fast, friendly and easy to learn programming language. From here to onward we will use Python 3.

Jupyter

The Jupyter Notebook is an open-source web application. It permits you to create and share documents which contain live code, visualizations, etc. Jupyter used for data cleaning and transformation, numerical simulation, statistical modeling, data visualization, machine learning, and so on.

Jupyter’s Interface – Dashboard: Snap of Jupyter’s Interface – Dashboard.

You can see in below picture the interface is very simple and easy to understands.

We will click on ‘New’ button to create a new Notebook Python 3, a new text file, folder or terminal. Therefore, we click on Notebook Python 3 to create it.

To execute the code press Shift + Enter

Generally, code option is selected but if you intend to write comments/message or documentation then you will select markdown cell option, this text will not be executed as shown in the figure.

From here to onward we mostly focused on practical examples to understand the basic concepts.

Variables      

Variables declaration in python is very simple. Look at the figure that will show you how to declare variables in python.

‘x’ is declared with initial value of 12. When we run the code, the output value ’12’ is printed.

Python variable declaration

Numbers and Boolean Values:

Integer

Positive or negative whole numbers but without decimal points e.g. 3, 6, -4, -12, etc.

Float

Real numbers having decimal point like 3.6, -4.12, etc.

Boolean Value

It is two values ‘true’ or ‘false’, 0 or 1, on or off.

Strings

Strings consist of a sequence of characters like ‘test’, ‘book’, etc. Firstly, we have written Karachi without any quotes or print statement. The result is error.

Now put the same string in quotes ‘Karachi’, or by using print (‘Karachi’) output success.

string declaration in python

Example of the concatenation of two strings is shown next. ‘+’ sign is used to concatenate the two strings.

string concatenation in python

Arithmetic Operators

Arithmetic operations are as simple as shown here. Simple operations of addition, multiplication, division, and multiplication are given. You may have noticed x = 3 **2. The out is 9. What does it mean? It means that power of 3 is raised to 2.

The last operation with % operator gives use remainder 2.

SHORT KEYS:

            Few important shortcuts are given as under: –

Key Purpose
Ctrl + Enter Code execution
Shift + Enter Code execution with new line
Double click on D Select cell or input field and then double click on D to delete the cell or input field
\ (back slash) Line continuation

Comparison, Logical and Identity Operators:

Comparison Operators

Operator Description
= = Double equal signs verify the equality on both left and right sides
! = It verify left and right sides are not equal
Greater than sign
Less than sign
> = Greater than and equal to
< = Less than and equal to

Logical Operators

Operator Description
And Checks whether the two statements around it are ‘True’
Or Checks whether at least one out of two statements is ‘True’
Not It leads to the opposite of the given statement if ‘true’ leads to ‘false’ and vice versa.

Identity Operators

Word Description
Is Checks whether the two statements around it are ‘True’
Is not Checks whether the two statements around it are ‘True’

Operator precedence:

Not,  And & then OR operator. A practical example of these operators are shown below,

logical operators in python
5 == 6
4 == 4
4 != 5
4 is 5
4 is not 5

Adding Comments

Adding comments is an essential part of any programming language that will be helpful during coding and for future utilization of code. For commenting, hashtag # is used, see this example.

adding comments in python
# This is just comment that will not effect on coding at all
x = 3 * 12
x

Indexing Elements:

Syntax: “name of variable”[index of element]. In indexing, square brackets [] must be used instead of parentheses () and braces {}.

indexing elements in python

It is pertinent to note that Python starts counting from 0 instead of 1. In our above example, the 4th letter is ‘s’.

Conditional Statements (If, Elseif):

Basic Syntax of 'if' statement in python
Basic Syntax of 'if' statement
if condition
  conditional code
if 5 == 5:
   print ('Right')
syntax of 'if else statement in python
syntax of 'if else statement
if condition
  condition code
else
  else code
if 5 == 6:
   print ('Right')
else:
   print ('Wrong')
syntax of "if elif else' statement in python
syntax of "if elif' statement
if condition
   conditional code
elif
   conditional code
else
   else code
if 6 > 5:
   print ('Yes')
elif 6 < 5:
   print ('No') 
else:
   print ('Blank')

While Loop:

while loop syntax python
a = 0
while a <= 10:
    print (a)
    a = a + 2

Creating a Function with a parameter:

Creating a Function with a parameter:
def sample(x):
    return x + 5

sample(3)

Creating multiple functions with a few parameters:

def sample(x,y,z):
    result = x + y + z
    print ('parameter x equals', x)
    print ('parameter y equals', y) 
    print ('parameter z equals', z)
    return result 

sample (2,4,6)

Built-in Functions in Python:

Function  Description
int() Convert its arguments in integer data type
float() Convert its argument in float data type
str() Convert its argument in string data type
abs() Get the absolute value of its argument
sum() Calculate the sum of all the elements
max() Give the highest value from a sequence of a numbers
min() Give the minimum value from a sequence of a numbers
len() It return the number of elements in an object
round(x,y) It returns the float of its argument(x), rounded to a specified number of digits(y) after the decimal point
pow(x,y) It return x to the power of y

Lists:

It is a type of sequence of data points like, integers, strings or floats.

python lists
students = ['Shahid', 'Khalid', 'Ali']
students

students[1]
students[-1]

Tuples:

It is also a type of sequence of data points but tuples cannot be modified.

tuples in python
a = (12, 4, 6)
a

x, y, z = 2, 4, 6
z

Dictionaries:

It is another way of storing data.

dictionaries in python
dict = {'d1': "Apple", 'd2': "Mango"}
dict['d1']

Built-in Methods (Append and Extend):

Built-in Methods (Append and Extend):
Passengers =['Shahid', 'Khalid', 'Ali']
Passengers

Passengers.append("Rizwan")
Passengers

Passengers.extend(["Jan"])
Passengers
Syntax:            
object.method()

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