Python: Decision Making

Every day we make decisions. When I get up in the morning, I need my shake. Now, for the shake, I need 500 ml Milk, 100 gms of Oats, 1 Banana, 1 Kiwi, and 1 Apple. In case, I don’t have any one of these, it can spell trouble. What’s the trouble ? I cannot make my shake.

In programming, we have a similar structure to situations such as these. Decision making is done with a set of statements called if, else-if, and else.

If: If a certain condition is met, we perform a block of code.
Else-if: If the IF condition is not met, we perform the code written in else-if
Else: If the IF condition, and the ELSE-IF condition are both not met, we perform this block of code.

Sr.No.Statement & Description
1An if statement consists of a boolean expression followed by one or more statements.
2An elif statement is python’s way of saying “if the previous conditions were not true, then try this condition”.
3The else keyword catches anything which isn’t caught by the preceding conditions.

A more picturesque, and descriptive version can be seen in this image below:

func.in: An image representing if-else statements. The order of preference is 1, 2, and then 3 .

IF statement

Example:

x = 33
y = 200
if y > x:
  print(“y is greater than x”)

Output:

y is greater than x

Please note the indentation. In Python, we use indentations as a way of saying that the code which follows the statement is enclosed. In other programming languages, we tend to use braces, or a parenthesis for the same. In python, things are slightly simpler, and we use indentations.

ELIF statement

Example:

x = 56
y = 56
if x > y:
  print(“x is greater than y”)
elif x == y:
  print(“x and y are equal”)

Output:

x and y are equal

From the above example, we can see that because a and b both have equal values, the first block was not satisfied. Instead, the second block of code under elif, has been executed.

ELSE statement

Example:

x = 100
y = 50
if x > y:
  print(“x is greater than y”)
elif x == y:
  print(“x and y are equal”)
else:
  print(“x is greater than y”)

Output:

x is greater than y

Python: Operators

The heart, the soul, and the foundation of any programming language, are it’s operators. They help build the logic, and transform your ideas into functioning models. They can manipulate values, functions, and help achieve our targets when used effectively.

Types of Operators

Python language supports the following types of operators.

  • Arithmetic
  • Assignment
  • Bitwise
  • Comparison (Relational)
  • Identity
  • Logical
  • Membership

Now, we shall look at each arithmetic operator with examples, so that it will be a lot easier for one to understand, how does Python, and their operators, really work!

Python Arithmetic Operators

Let’s assume we have two variable, a =5 and b = 10. Thus:

OperatorDescriptionExample
+ AdditionAdds values on either side of the operator.a + b = 15
– SubtractionSubtracts right hand operand from left hand operand.a – b = -5
* MultiplicationMultiplies values on either side of the operatora * b = 50
/ DivisionDivides left hand operand by right hand operandb / a = 2
% ModulusDivides left hand operand by right hand operand and returns remainderb % a = 0
** ExponentPerforms exponential (power) calculation on operatorsa**b =
5 to the power 10
//Floor Division – The division of operands where the result is the quotient in which the digits after the decimal point are removed. But if one of the operands is negative, the result is floored, i.e., rounded away from zero (towards negative infinity) −9//2 = 4 and 9.0//2.0 = 4.0, -11//3 = -4, -11.0//3 = -4.0

Python Comparison Operators

These operators compare the values on either sides of them and decide the relation among them. They are also called Relational operators.

Let’s assume we have two variable, a =5 and b = 10. Thus:

OperatorDescriptionExample
==If the values of two operands are equal, then the condition becomes true.(a == b) is not true.
!=If values of two operands are not equal, then condition becomes true.(a != b) is true.
<>If values of two operands are not equal, then condition becomes true.(a <> b) is true. This is similar to != operator.
>If the value of left operand is greater than the value of right operand, then condition becomes true.(a > b) is not true.
<If the value of left operand is less than the value of right operand, then condition becomes true.(a < b) is true.
>=If the value of left operand is greater than or equal to the value of right operand, then condition becomes true.(a >= b) is not true.
<=If the value of left operand is less than or equal to the value of right operand, then condition becomes true.(a <= b) is true.

Python Assignment Operators

Let’s assume we have two variable, a =5 and b = 10. Thus:

OperatorDescriptionExample
=Assigns values from right side operands to left side operandc = a + b assigns value of a + b into c
+= Add ANDIt adds right operand to the left operand and assign the result to left operandc += a is equivalent to c = c + a
-= Subtract ANDIt subtracts right operand from the left operand and assign the result to left operandc -= a is equivalent to c = c – a
*= Multiply ANDIt multiplies right operand with the left operand and assign the result to left operandc *= a is equivalent to c = c * a
/= Divide ANDIt divides left operand with the right operand and assign the result to left operandc /= a is equivalent to c = c / ac /= a is equivalent to c = c / a
%= Modulus ANDIt takes modulus using two operands and assign the result to left operandc %= a is equivalent to c = c % a
**= Exponent ANDPerforms exponential (power) calculation on operators and assign value to the left operandc **= a is equivalent to c = c ** a
//= Floor DivisionIt performs floor division on operators and assign value to the left operandc //= a is equivalent to c = c // a

Python Bitwise Operators

Bitwise operator works on bits and performs bit by bit operation. Assume if a = 60; and b = 13; Now in binary format they will be as follows −

a = 0011 1100

b = 0000 1101

—————–

a&b = 0000 1100

a|b = 0011 1101

a^b = 0011 0001

~a  = 1100 0011

There are following Bitwise operators supported by Python language

OperatorDescriptionExample
& Binary ANDOperator copies a bit to the result if it exists in both operands(a & b) (means 0000 1100)
| Binary ORIt copies a bit if it exists in either operand.(a | b) = 61 (means 0011 1101)
^ Binary XORIt copies the bit if it is set in one operand but not both.(a ^ b) = 49 (means 0011 0001)
~ Binary Ones ComplementIt is unary and has the effect of ‘flipping’ bits.(~a ) = -61 (means 1100 0011 in 2’s complement form due to a signed binary number.
<< Binary Left ShiftThe left operands value is moved left by the number of bits specified by the right operand.a << 2 = 240 (means 1111 0000)
>> Binary Right ShiftThe left operands value is moved right by the number of bits specified by the right operand.a >> 2 = 15 (means 0000 1111)

Python Logical Operators

There are following logical operators supported by Python language. Let’s assume we have two variable, a =5 and b = 10. Thus:

OperatorDescriptionExample
and Logical ANDIf both the operands are true then condition becomes true.(a and b) is true.
or Logical ORIf any of the two operands are non-zero then condition becomes true.(a or b) is true.
not Logical NOTUsed to reverse the logical state of its operand.Not(a and b) is false.

Python Membership Operators

Python’s membership operators test for membership in a sequence, such as strings, lists, or tuples. There are two membership operators as explained below:

OperatorDescriptionExample
inEvaluates to true if it finds a variable in the specified sequence and false otherwise.x in y, here in results in a 1 if x is a member of sequence y.
not inEvaluates to true if it does not finds a variable in the specified sequence and false otherwise.x not in y, here not in results in a 1 if x is not a member of sequence y.

Python Identity Operators

Identity operators compare the memory locations of two objects. There are two Identity operators explained below −

OperatorDescriptionExample
isEvaluates to true if the variables on either side of the operator point to the same object and false otherwise.x is y, here is results in 1 if id(x) equals id(y).
is notEvaluates to false if the variables on either side of the operator point to the same object and true otherwise.x is not y, here is not results in 1 if id(x) is not equal to id(y).

Python Operators Precedence

The following table lists all operators from highest precedence to lowest.

Sr.No.Operator & Description
1** Exponentiation (raise to the power)
2~ + – Complement, unary plus and minus (method names for the last two are +@ and -@)
3* / % // Multiply, divide, modulo and floor division
4+ – Addition and subtraction
5>> << Right and left bitwise shift
6&Bitwise ‘AND’
7^ |Bitwise exclusive `OR’ and regular `OR’
8<= < > >= Comparison operators
9<> == != Equality operators
10= %= /= //= -= += *= **= Assignment operators
11is is not Identity operators
12in not in Membership operators
13not or and Logical operators

In case, you have any questions, feel free to mention your questions as comments to this specific post. I will try and answer at the earliest.

Python: Variables

The word variable in itself speaks dynamism. It’s value, quantity, and essence, can change from time to time. In programming as well, your value changes from time to time.

In Python, variables are used to store data, like string, numbers, date-time etc. When you create a variable, a little portion is reserved within your computer memory to store this value of the variable. The value of a variable has to be assigned by you.

Types of variables

Python has five standard data types:

  • Numbers
  • String
  • List
  • Tuple
  • Dictionary

Creating a variable

In Python, a variable does not need to be declared while creating or before adding a value to it. Python variables are usually dynamically typed, that is, the type of the variable is interpreted during run-time and you don’t need to specify the type of a variable.

The following program shows how to use string and integer type variables:

Example

x = 10 # Integer variable
y = “Hello World” # String variable
# Displaying variables value
print(x)
print(y)

Output

10
Hello World

Checking the type of a variable

With the method type(), we can know the type of variable we have created. It could be int, str, is used to get the type of a created variable.

Example

var1 = ‘Hello World’
print(type(var1))

Output

<class ‘str’>

Important Rules for Variables

  • Variables cannot start with a number, but can be Alpha-Numeric. Additionally, they also support underscores – hence the total range is from A-Z, a-z, 0-9, and _.
  • Variables are strictly case-sensitive, thus You and you are different variables

Data Type Conversion

Sometimes, due to functional reasons, we need to convert variables. For this purpose, python is quite straight forward. To convert between types, you simply use the type name as a function. A common industry jargon is ‘Type Casting‘.

There are several built-in functions to perform conversion from one data type to another. These functions return a new object, with the changed data type 🙂.

Sr.No.Function & Description
1int(x ): Converts x to an integer.
2long(x): Converts x to a long integer.
3float(x): Converts x to a floating-point number.
4str(x): Converts object x to a string representation.
5tuple(s): Converts s to a tuple.
6list(s): Converts s to a list.
7set(s): Converts s to a set.
8dict(d): Creates a dictionary. d must be a sequence of (key,value) tuples.
9chr(x): Converts an integer to a character.

An introduction to Python

You have no idea how long I have waited to have my own portal in order to share information, with one, and all. With a lot of patience, time, and effort, I’d like to begin my journey of being an open book, solving some of your problems, and in that process also learning a lot more from you.

To begin with, I would like to introduce Python to you as a concept I like to call SEQLSimple Elegant Quick Learn. So instead of SQL, we have SEQL.

Python is a popular programming language. It was created by Guido van Rossum, and released in 1991, and has a wide array of uses, particularly:

  • Web Development
  • Software Development,
  • Scripting
  • Machine Learning
  • Artificial Intelligence

Owing to it’s Simple syntax, and an Elegant programming structure, it is Quick to execute and Learn. Over the course of my forthcoming posts, you shall come across a wide range of tutorials, quick solutions, tips, and tricks, that I have documented, learned, and experienced over time.

With my trivial, yet foundational, exposure to Python, I want to document my understanding of programming, and make it as easy for you to grasp the fundamental concepts of programming.

In case you have any doubts, feel free to write down your questions in the comments below. I will try and respond to each one of them.

Before I leave, one has to cut the ribbon by a simple saying….wait for it….”Hello World”.

So how does one do that ? Well, you just type:

print(“Hello, World!”)

The output should read:

Hello, World!