Python Basics and Intro to Data Types | AI Planet (formerly DPhi)

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When writing code in Python, it's important to ensure that your code can be easily understood by others, say by your friend who wants to see your code.
Python ignores everything after the hash mark and up to the end of the line. You can insert them anywhere in your code!
A shortcut for adding comments is by using CTRL + /
Simply select all the lines you want to comment out, then press Ctrl + /, and all the lines will get commented out!

Operators perform simple additions, comparisons, etc., on variables and values.
Python supports the following types of operators; we will look at some commonly used operators.

Using Python, we can perform some basic arithmetic operations such as addition, subtraction, multiplication, etc.

Example:

x = 2
y = 3
x + y # addition
x * y # multiplication

A variable can be considered as a storage container for data.
Every variable will have a name.
It is a good way to store information while making it easy to refer to that information in our code later.

For instance, instead of working with the number 3.14, we can assign it to a variable pi and use it as many times as we want in our code (wherever required).
The equal sign (=) is used to assign values to variables.
The syntax for assigning values to a variable is as follows: Variable name = value or information.
Example:
- x = 5
- y = "John"

If you're learning Python from multiple sources, you might encounter the terms data structures and data types being used interchangeably.
Definition: Data structure is a general computer science concept. Its definition reads as follows on Wikipedia:
Data structure is a data organization, management, and storage format that enables efficient access and modification. More precisely, a data structure is a collection of data values, their relationships, and the functions or operations that can be applied to the data.
Whereas Data type is a concept specific to a programming language. In a way, it is a concrete implementation of a data structure in a particular programming language (Python or any other language).
The definition of what constitutes a "type" varies among programming languages. Talking about Python, there are basic data types like int, float, string, etc. You can use the built-in types like list, set, etc., which we will cover in this session.
Calling these data types as data structures won't be wrong because there is no significant difference between the two in Python.

Before we proceed to discuss what data types in Python are, there are some basic questions that we will discuss. What is data?
Let's say you are going to meet a friend at her office. When you go to visit her office, the security guard asks you to make an entry in the register before you enter the office. A typical entry register asks for the following information –


Visitor's name	Visitor's phone number	Visitor's address	Entry time
Karen	32 000 000	Leuven	8:30 AM

The above information that you just provided is data.
We see that the data entered in the previous slide has different varieties:
- Some are English letters,
- Some are numerical digits, and
- There are some special characters, dash (-) and colon ( : ).
- In this example, our data is divided into four categories – name, phone number, address, and time.
- This categorization of data, based on their characteristic & our need, is called data types.
Some of the data types in Python include:
- Integer: whole numbers, positive or negative numbers. E.g., 100
- Float: Floating-point numbers are real numbers, rational or irrational. In most cases, this means numbers with decimal fractions. Example: 123.45
- String: Strings are sequences of characters, or text, enclosed in quotes. Example: "any text", "Karen" \
For further reading:
- operators and data types
For practice and different data type examples, visit: https://www.w3schools.com/python/python_datatypes.asp

You can get the data type of any object by using the type( ) function:

Sequences allow you to store multiple values in an organized and efficient way.
There are seven sequence types: strings, Unicode strings, lists, tuples, bytearrays, buffers, and xrange objects.
Nothing to worry about looking at this long list; you will get to know it gradually.

Strings are a sequence of characters.
Let us see some examples of String: "My name is Rahul", "Rahul", "Go home". All these are examples of String.
In Python, Strings are called str.
There is a specific way of defining String in Python – it is defined within single quotes (') or double quotes ("), or even triple quotes (''').

Square brackets can be used to access elements of the string.
Remember that the first character has index 0.
Index refers to the position of a character in a string. In python index number starts from 0.
Example:
```
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a = "Hello, World!"
print(a[1])
```
Will give an output e. Can you understand why?

We can also call out a range of characters from the string using string slicing.
Specify the start and end indexes separated by a colon to return a part of the string. Note that the character of the end index is not included.
Suppose we want to print World from the "Hello World" string. We can do so as below:

If we have a long string and we want to pinpoint an item towards the end, we can also count backward from the end of the string, starting at the index number -1
Printing 'r' from the string :
```
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a = "Hello, World!"
print(a[-4])
```
Get the characters from position -5 to position -1, starting the count from the end of the string:
1print(a[-5:-2])
Will give an output: orl

Another example:

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x = "Python is "
y = "awesome"
z =  x + y
print(z)

Python has a set of built-in methods you can use on strings.
Must learn: Learn about important string methods from the below cheatsheet: https://www.codecademy.com/learn/learn-python-3/modules/learn-python3-strings/cheatsheet
Tip: If you cannot follow, run the code and make out the difference.