Python Introduction

Python

Python

Python is a popular high-level programming language that is used in various fields such as web development, data science, and software engineering. Python is known for its readability, simplicity, and versatility.

Print Statements

In python and like many programming languages, they have print statements. These are what you can use to make the program display an output to the computer screen when you are programming.

Here’s an example of a print statement that displays the words “Hello World”:

print("Hello World")

When you run the program this is the output:

Hello World

Comments

In python there are these things called comments. Comments are like notes or reminders that we write in our code to help us understand it better.

For example in python we can use a comment like this:

# This is a comment

Here is another example of a comment being used.

# This code prints the words "Hello World"
print("Hello World")

Output:

Hello World

As we can see comments dont effect the code in any way and they are just there for you as the programmer to see.

Variables and Data Types

Variables in Python are like containers that hold information. Imagine a box with a label on it. You can put different things in the box, and the label helps you remember what’s inside. Similarly, a variable has a name (like the label) and can store different types of information, such as numbers, words, or true/false values.

For example, let’s say we have a variable called ‘age’ to store someone’s age:

age = 15

Here, ‘age’ is the variable name, and ‘15’ is the value stored in the variable. Later, if the person’s age changes, we can update the variable:

age = 16

Now, ‘age’ holds the value ‘16’. Variables allow us to store and manipulate data in our programs, making them flexible and powerful.”

We can also use print statements to display the information that is stored in variables. Now lets see an example.

Here we have a variable called “message” that stores the text “Hi how are you?”, and a print statement with the variable “message” inside of it.

message = "Hi how are you?"
print(message)

When we run the program this is what gets outputted:

Hi how are you?

In python data types are essentially different kinds of containers that store different types of information. Just like in real life, where we have different types of containers for storing different things (like a box for toys, a jar for cookies, and a bottle for water), Python has different data types for storing different kinds of information.

You can use these data types for storing different types of data in variables.

Here are some common data types in python:

String (str): Strings are used for storing text, like ‘hello’ or ‘Python is fun!’.

Integer (int): This data type is for storing whole numbers, like 5, 10, or -3.

Float (float): Floats are used for storing decimal numbers, like 3.14 or -0.5.

Boolean (bool): Booleans can only have two values: True or False. They’re often used for making decisions in our programs, like ‘Is it raining? (True/False)’.

List: Lists are used for storing collections of items. For example, a list of numbers [1, 2, 3] or a list of names [‘Alice’, ‘Bob’, ‘Charlie’].

Here are some examples of these different data types.

This is a variable named “message” that contains a String (str) data type.

message = "Hello World"

This is a variable named number that contains an Integer (int) data type.

number = 10

This is a variable named “decimal_number” that contains a FLoat (float) data type.

decimal_number = 15.5

This is a variable named “currently_learning” that contains a Boolean (bool) data type.

currently_learning = True

This is a list variable named “number_list” that is a list data type that contains a list of Integers. Lists can also contain Strings.

number_list = [1, 2, 3]

In python we can also store a variable inside of a variable and give them new values.

Here we have the variable age that holds the value of 15. We also have the variable called new_age that holds the value of 16.

age = 15
new_age = 16

print(age) 
age = new_age
print(age)

When the first print statement gets ran, the number 15 gets printed but when the second print statement runs, the number 16 gets printed. This is because when we did age = new_age, we are giving the age variable a new value which is the value of new age.

Output:

15
16

Operators

Mathematical Operators

In Python there are arithmetic operators that are used to perform basic mathematical operations like addition, subtraction, multiplication, and division.

Operator	Description	Syntax
+	Addition: adds two operands	x + y
-	Subtraction: subtracts two operands	x - y
*	Multiplication: multiplies two operands	x * y
/	Division: divides the first operand by the second	x / y

Here are some examples of how to use these operators:

print(5 + 5) 
print(5 - 1) 
print(5 * 5)
print(10 / 2) 

When we run the program all of these print statements get called and the answers to these mathematical operations get printed (outputted).

We can also use variables that hold values to perform these mathematical operations.

number_five = 5
number_two = 2
number_one = 1
number_ten = 10

print(number_five + number_five)
print(number_five - number_one)
print(number_five * number_five)
print(number_ten / number_two)

Here is the output:

Aditionally we can use expressions which are like sentences in math that help us do calculations and solve problems. Here are some examples.

x = 20
y = 10
  
add = x + y 
subtract = x - y 
multiply = x * y 
divide = x / y 
  
print(add) 
print(sub) 
print(pro) 
print(div)

Here is what the output of this code would look like:

In Python we can also add Strings together. This is called concatenation. Concatenation in Python is like combining pieces of text or data together to create a single, larger piece. It’s like putting together pieces of a puzzle to make a bigger picture, or joining words to form a sentence.

Here is an example:

word_1 = "Hello"
word_2 = "World"
print(word1 + " " + word2)

Output:

Hello World

Concatenation is not limited to strings. We can also concatenate things like lists. For example:

list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined_list = list1 + list2
print(combined_list)  

Output:

[1, 2, 3, 4, 5, 6]

Comparison Operators

In Python Comparison operators compare values. It either returns True or False according to the condition.

Operator	Description	Syntax
>	Greater than: True if the left operand is greater than the right	x > y
<	Less than: True if the left operand is less than the right	x < y
==	Equal to: True if both operands are equal	x == y
!=	Not equal to: True if operands are not equal	x != y
>=	Greater than or equal to: True if the left operand is greater than or equal to the right	x >= y
<=	Less than or equal to: True if the left operand is less than or equal to the right	x <= y

Here are some examples of them being used:

a = 15
b = 5
  
print(a > b) # since a is greater than b, the print statement returns True

print(a < b) # since a is less than b, the print statement returns False

print(a == b) # since a is not equal to b, the print statement returns False

print(a != b) # since a is not equal to b, the print statement returns True

print(a >= b) # since a is either greater than or equal to b, the print statement returns True

print(a <= b) # since a is either not less than or equal to b, the print statement returns False

Here is the output of this code:

True
False
False
True
True
False

Logical Opersators

Logical operators in Python are like tools we use to make decisions in our programs. Just like how you might use the words ‘and’, ‘or’, and ‘not’ to combine ideas or conditions when you’re making a decision in real life, logical operators in Python help us combine conditions and make decisions in our code.

Operator	Description	Syntax
and	Logical AND: True if both the operands are true	x and y
or	Logical OR: True if either of the operands is true	x or y
not	Logical NOT: True if the operand is false	not x

Here are some examples on how to use them.

a = True
b = False
print(a and b) # returns False because b is False. If they were both True then it would return True.

print(a or b) # returns True because at least one of them is True which in this case is a.

print(not a) # returns False because a is True. 

print(not b) # returns True because b is False. 

Output:

False 
True
False
True

Identity And Membership Operators

Identity operators in Python are like tools we use to check if two things are the same or different. Just like how you might compare two things in real life to see if they are identical or not.

Operator	Description	Syntax
is	True if the operands are identical	x is y
is not	True if the operands are not identical	x is not y

Here are some examples for how we can use them.

a = 10
b = 20
  
print(a is b) # returns False because this is checking if a and b are the same but they are not.

print(a is not b) # returns True because this is checking if a is not equal to b which is True.

Output:

False 
True

Membership operators in Python are like tools we use to check if something is part of a group or sequence. It’s like looking for a specific item in a collection, such as finding a book in a library or checking if your name is on a list.

Operator	Description	Syntax
in	True if value is found in the sequence	x in y
not in	True if value is not found in the sequence	x not in y

Here are some examples:

In this example we have a list of numbers and we are printing True if 6 is in the list and False if it is not.

numbers = [1, 2, 3, 4, 5] 
print(6 in numbers) 

Output:

False

Since 6 was not in the list, this statement prints False.

In this next example we have a list of numbers and we are printing True if 9 is not in the list and True if it is.

numbers = [1, 2, 3, 4, 5] 
print(9 not in numbers) 

Output:

True

Since 9 was not in the list, this statement prints True.

Aditionally we can also use this for Strings.

sentence = "hello how are you"
print("how" in sentence) 

Output:

True

This prints True because the text “how” is found inside of the text “hello how are you”.

if and else Statements

If statements in Python are like decision-making tools that help our programs make choices based on certain conditions. It is used to decide whether certain code will be executed or not.

Here is an example of the format of using an if statement.

if condition:
   # code to execute if the condition is true

Here is an example of an if statement with code to check if a number is positive.

number = 5
if number > 0: 
   print("The number " + str(number) + " is positive) 

Output:

The number 5 is positive

What happend was that since the number 5 was greater than zero, it printed “The number 5 is positive” and if it wasnt then nothing would be printed since the condition would be false in that situation. We also used type conversion str(number) because we cannot add an integer and a string together so we had to convert the integer of 5 into a string so there wouldn’t be an error.

Else Statements

In Python Else statements are like a backup plan that gets executed when the conditions specified in the if statement are not met.

For example lets say that we have this code that checks if a person is an adult.

age = 19

if age >= 18:
   print("Your age is 18 or greater so you are an adult")

Output

Your age 18 or greater so you are an adult

This code works but it is not really useful because if the user is under 18 then nothing will happen and there will be no output.

Here is how we can fix this with else statements:

age = 16

if age >= 18:
   print("Your age is 18 or greater so you are an adult")
else: 
   print("Your age is under 18 so you are not an adult")

Output

Your age is under 18 so you are not an adult

Else If Statements

In Python there are also else if or elif statements that act similar to else statements but you use them when you want to check another condition.

Here is an example of using elif statements to see what type of grade you have:

grade = 87

if grade >= 90:
   print("You have an A")

elif grade >= 80:
   print("You have a B")
   
elif grade >= 70:
   print("You have a C")

else:
   print("You have an F")

Output

You have a B

Lists

In Python lists are a data structure that we use to store multiple items is a singular variable. They can also contain elements of different data types. Lists can easily be modiefied and its data can easily be accessed.

Here is how you can create a list with 5 integer elements ranging from 1 to 5:

my_list = [1,2,3,4,5]

Here is an example of a list of strings:

my_list = ["apple", "orange", "banana"]

Accessing Elements

In programming languages they use what’s called zero indexing where essentially the first index of a data structure like lists or strings starts at zero.

So in this example to access the first element of the list we would do this:

my_list = ["apple", "orange", "banana"]
print(my_list[0])

Output:

apple

Modifying Elements

Here’s how we can modify the list:

my_list = ["apple", "orange", "banana"]
my_list[1] = "pear"
print(my_list)

Output:

apple, pear, banana

Adding Elements

For adding elements to the list we can use a list method which is a built in method that we csan use on lists. To add elements we can use the .append() method.

Here’s an example:

my_list = ["apple", "orange", "banana"]
my_list.append("cherry")
print(my_list)

Output:

apple, orange, banana, cherry

Removing Elements

For removing elements we can use the .remove() method.

Example:

my_list = ["apple", "orange", "banana"]
my_list.remove(2)
print(my_list)

Output:

apple, orange

List Length

We can access the length of a list by using the len method which looks like this len(). The len method can also be used for other data structures and types like strings.

Here is how we can use it with iterating over a list:

my_list = ["apple", "orange", "banana"]

print(len(my_list))

Output:

Loops

We can use loops for when we want to execute code repeatedly until a specific condition is met. In Python there are two main loops which are the for and while loops. The while loop is used when you want to ececute code until a specific condition is true and the for loop is when you know how many times you want the code to execute.

For loop

We can use for loops to iterate over a list or a range of numbers.

Here is an example of using a for loop for iterating over a list:

my_list = ["apple", "orange", "banana"]

for item in my_list:
   print(my_list[item])

Output:

apple
orange
banana

This is how we would use it with a range of numbers:

for x in range(5)
   print(x)

Output:

While Loop

We use while loops when we want to execute code until a condition is met then once the condition is met then the loop stops.

For example her is how we can print numbers from 1 to 5:

number = 0
while number < 5:
   number +=1
   print(number)

Output:

Functions

In Python we can use funnctions which is a block of organized, reusable code that performs a specific task. Functions provide a way to modularize your code, making it easier to read, write, and maintain. In Python, you define a function using the def keyword followed by the function name, parentheses ( ) containing optional parameters, and a colon :. The body of the function is indented and contains the code to be executed when the function is called.

Here’s an example of a function that takes a users name and prints it with hello:

def greeting(name):
   print("Hello " + name + "!")

greeting("programmer")  # This is how you call the function (use it)

Output:

Hello programmer!

Functions can also return values using a return statement.

Here is an example of a function that adds two numbers togther and returns it:

def add(x, y): 
   return x + y

# Call the function and store the result in a variable
result = add(3, 5)
print(result)

Output:

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Python Introduction

Table of contents

Python

Print Statements

Comments

Variables and Data Types

Operators

Mathematical Operators

Comparison Operators

Logical Opersators

Identity And Membership Operators

if and else Statements

Else Statements

Else If Statements

Lists

Loops

Functions