Introduction to Python
Google uses Python extensively in its web search systems and even employed Guido van Rossum, the inventor of Python.
Intro to Data Types and Variables
How to Code Data Types & Variables in Python (String & Integer Variables)
Python syntax is straightforward and easy to understand, making it great for both beginners and experienced programmers.
Understanding syntax is like learning the grammar of a language. It is the base for all your future coding projects.
So, let’s start by talking about variables.
Let’s write our first line of code together. We are going to create a variable named name and assign it the value “Apsock”.
Here’s how we do it: name = "Apsock". The word Apsock is in quotes because it is a string.
We have created a variable called name and given it the value “Apsock”.
Now, let’s go to Google Colab, which we will call Colab from now on.
Click on “New” and then “New Notebook”. In the new notebook, enter the following code: name = "Apsock".
When you run the code by pressing the play button, it might seem like nothing happened, but something did. We told Python that our variable name has the value “Apsock”.
You can also use single quotes instead of double quotes, and it will work the same way. For example: name = 'Apsock'.
Python knows that what we just created is a string because we put Apsock in quotes. Strings are a type of data in Python. Think of strings as text or anything in quotes.
Strings can get more complicated, and we will build on this throughout the course. It’s important to note that Python is case-sensitive.
If we change the code to use uppercase letters, like String, we will get an error because Python recognizes string and String as different.
Now, there are different types of data, or data types, in Python.
Let’s discuss another data type called int, which stands for integer. An integer is a whole number, like one, two, or three.
What if we try to define the name Apsock as an integer and run the code? We would get an error because Apsock is not a number.
Let’s add another line of code to define age as 44: age = 44. Python knows that 44 is an integer.
We could also use int to get the same result: age = int(44).
Python is smart enough to understand that 44 is an integer, whether we write it directly or use the int function.
Functions
We used the print function to show “Hello World” to the user. This is called a function.
The print function has one goal: to show a message, or information, back to the user.
There are many built-in Python functions that make our lives easier by accomplishing specific tasks for us.
We can even define our own functions, which we will discuss in Level 4. In this level, we will talk about functions in more detail.
So, let’s go back to Colab together.
I want you to add a second line of code to Colab and print the variable called name. You can pause and try this in Colab, then press play to run the code.
Here’s how to use the print function to print the variable called name:
name = "Apsock"
print(name)
Notice we didn’t need to put quotes around name. This is because we already defined the variable name as “Apsock”.
Please remember to comment your code. This is important in case you come back to see your code in the future or if someone else needs to understand what you were trying to do.
We know that Python skips the commented line of code. You can also type comments after the code:
name = "Apsock" # This is a string variable
print(name) # This prints the name variable
How can we tell if a variable is a string or an integer? We can use the
type() function.
For example:
type(name) # This will tell us that 'name' is a string
We can also ask Python to tell us what type of variable
age is:
age = 44
type(age) # This will tell us that 'age' is an integer
Soon, we will discuss how to change a variable from a string to an integer. Changing a data type from one type to another is called casting.
Floating and Boolean Data Types
Now that we understand how to use string and integer data types, let’s talk about two more data types: float and Boolean.
Let’s start with floating point numbers, which are called float. An integer is a whole number like one, two, or three.
pi = 3.14
print(pi)
print(type(pi))
We get a data type of float. A float means a floating point number, which is a number that has decimal points. We can also specify it directly:
pi = float(3.14)
Another important data type is Boolean, which represents true or false values.
In programming, this can also be written as 0 or 1, where 1 means true and 0 means false.
Here’s an example using Boolean:
is_sunny = True
print(is_sunny)
print(type(is_sunny))
Notice that the ‘T’ in True is uppercase. It must be uppercase because lowercase ‘true’ will result in an error. We can also write it like this:
is_sunny = bool(True)
Replacing True with 1 gives the same result:
is_sunny = bool(1)
If we change 1 to 0, the result is False:
is_sunny = bool(0)
Why is this important?
In more advanced programming that we will do later in this book, we might want to use true or false logic to control the flow of our programs.
Understanding these basic data types is crucial as we build more complex applications.
How to Change the Content or Data Type of a Variable ("Casting")
Let’s say we have two lines of code as follows:
name = "Apsock"
print(name)
How do we change the contents of
name from “Apsock” to “Python”?
We can add a third line of code to make the change and a fourth line to print the updated variable:
name = "Apsock"
print(name)
name = "Python"
print(name)
Now, let’s discuss how to change a variable’s data type from a string to an integer.
In the previous chapters, we used str for strings, int for integers, float for floating-point numbers, and bool for Booleans to define our variables in different data types.
Let’s make a variable called age, and instead of setting it to 100, let’s define this number in double quotes:
age = "100"
Python interprets
age as a string because we put 100 in quotes. To convert age from a string to an integer, we can use the following code:
age = int(age)
print(age)
print(type(age))
Another important thing to keep in mind is the consequence of converting a floating-point number to an integer.
When we convert a number that has a decimal point to an integer, everything after the decimal point is discarded, which means we lose some information.
For example:
pi = 3.14
pi_as_int = int(pi)
print(pi_as_int)
No matter how close the floating-point number is to the next whole number, everything after the decimal point is discarded, and only the whole number part is kept.
This process does not round the number; it simply cuts off the decimal part. Later in this course, we will discuss how to use the rounding function to handle such cases more precisely.
EXERCISE
- Define name as a string variable & call it Apsock Python
- Print the name Apsock Python
- Define age as an integer variable and make it 35
- Print the age
- Define a Boolean variable called i cannot do it as false
- Print the variable
- Define a floating variable called the answer as 42.01
- Print the variable
Please complete the following steps below:
C3P0 is 1.75 meters tall & R2D2 is 1.09 meters tall.
Step 1: Create a variable called height as a string type
Step 2: Assign the height a value of 1.09
Step 3: Print the height of R2D2
Step 4: Change the height data type from string to floating
Step 5: Add 0.66 to 1.09
Step 6: Print the new height
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Other Lecture
Data Types & Variables
Why do we need to know if a data type is text or a number? Because Python needs to understand if an item is a number to perform calculations with it.
Python Math: Operator & String
Once we have a variable of a data type in python that is either an integer or a float, we can perform mathematical operations on it.
Built in Function & Creating Function in Python
Why should we learn to use Python built-in functions? Because they can save us a lot of time when we’re programming.
Python List Data Type
We already discussed how to use several data types. Now, we’ll talk about another data type called list.