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‎curriculum/01-foundations/01.01-output-variable-datatypes.md‎

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---
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id: output-variable-datatypes
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title: Outputting, Storing and Representing Data
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sidebar_label: 01.01 - Outputting, Storing and Representing Data
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sidebar_position: 1
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lesson: true
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---
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# Outputting, Storing and Representing Data
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Welcome to the first real python lesson. Our programs need a way to output information back to users and they also need to store various data to perform operations on them. We will learn how to do these things in the following lesson.
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## Lesson Overview
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At the end of the lesson you will:
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* Know how to output information to users screen
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* Know what is a **variable** and how to store values to them
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* Know core python data types:
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* Integer
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* Float
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* String
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* Boolean
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* Know how to represent missing values
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## Outputting Data Back to User
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In Python, we use `print` function to output some data back to user.
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```python interactive
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print(5)
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```
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Whatever you pass into the function will be outputted to the screen.
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We can also *print* multiple things at once, with python inserting space between each **argument**.
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```python interactive
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print(2, 5)
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```
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## Declaring Variables
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You can think of **variables** as boxes where your program stores various data. Python does not require any special syntax for declaring variables.
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**Variables** are defined by *assignment*.
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```python
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my_variable = 5
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```
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Declaring variables has some rules:
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* It must start with a letter or underscore
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* It can contain lowercase and uppercase letters, underscores, and numbers
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Styling guide **PEP8** suggests the use of `snake_case` for variable naming in python.
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:::tip
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See [PEP8 - Style Guide for Python Code](https://peps.python.org/pep-0008/) to learn more about style of writing python code.
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:::
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## Python Core Data Types
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Python has 4 core data types with addition of `None` which is a special value representing **no value**.
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:::note
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Python has a special `type()` function which returns what type some data is. We will use this to inspect the following data types.
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:::
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### Integer
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Integers represent **whole numbers**. We use them to represent age of user, score of the game and similar things.
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In Python, they are represented as `int`.
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```python interactive
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my_int = 5
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print(type(my_int))
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print(my_int)
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```
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### Float
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Floats represent **real numbers**. We use them to represent prices in shop and various other purposes.
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In Python, they are represented as `float`
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```python interactive
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my_float = 1.25
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print(type(my_float))
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print(my_float)
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```
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### String
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Strings represents **text** data. We use them to represent names, titles, descriptions and various other purposes.
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In Python, they are represented as `str` and must be wrapped with single (`'`) or double (`"`) quotes.
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```python interactive
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string1 = "Double quoted string"
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string2 = "Single quoted string"
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print(type(string1), type(string2))
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print(string1, string2)
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```
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**Strings** can have special characters called **escape character**. That character is a single **backslash** (`\`). Most common usecase is `\n` which tells Python that the rest of the string goes on the new line.
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```python interactive
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a = "Hello \n World"
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print(a)
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```
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### Boolean
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Boolean values represent **yes** or **no** state. We use them to represent if something is *true* or *false*.
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In Python, they are represented as `bool` and only two valid values are `True` or `False`.
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```python interactive
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bool1 = True
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bool2 = False
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print(type(bool1), type(bool2))
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print(bool1, bool2)
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```
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### None
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This special value `None` represents when there is no value. Its *type* is a special **NoneType**. Its useful when some of the data is missing or arriving at a later time.
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```python interactive
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none_value = None
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print(type(none_value))
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print(none_value)
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```
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### Complex, Bytes, Bytearray
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Python has a built-in support for **complex** numbers, as well as for **bytes** representations, but we will deal with those later.
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## Type Casting
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Type casting refers to transforming one datatype to another. For example, to transform string `"32"` to integer `32`.
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```python interactive
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a = "32"
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print("Type:", type(a), "Value:", a)
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b = int(a)
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print("Type:", type(b), "Value:", b)
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```
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We can also convert to and from other types.
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```python interactive
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a = 5
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b = str(a)
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c = float(a)
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print("a=", a, "type=", type(a))
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print("b=", b, "type=", type(b))
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print("c=", c, "type=", type(c))
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```
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:::note
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If Python cannot convert one type to another, it will raise **ValueError**. This usually happens when you try to convert some *text* into *number* or *float*.
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Error are very helpful as they tell us exactly **what** is the issue and **where** they happened. If the errors did not exists, your programs would just silently die, and you would have to randomly guess where the issue is.
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We will learn how to read and deal with errors in later lessons.
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:::
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## Assignment
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Try the following exercise to establish your knowledge.
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We will define a *shop name* and *item* with various data types.
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1. Create a variable called `shop_name` and set its value to some **string**
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2. Create a variable called `item_name` and set its value to some **string**
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3. Create a variable called `item_quantity` and set its value to some **integer**
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4. Create a variable called `item_price` and set its value to some **float**
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5. Create a variable called `item_available` and set its value to some **boolean**
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6. Output all of these variables declared to the screen (you can use multiple print statements) following this format: `<variable name>: <variable value>`
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### Assignment Area
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Use our built in Python interpreter to solve your assignment.
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```python interactive
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# Write your assignment below
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```
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## Deepen Your Knowledge
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Go through these articles to deepen your knowledge about the topics covered in this lesson.
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1. Learn more about [Strings in Python](https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str) in **Official Python Documentation** and [What is String and its types in Python](https://dev.to/atifwattoo/what-is-string-and-its-types-in-python-4ide) from this article from **dev.to** .
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2. Read more about `print()` function from [Your Guide to Python print Function](https://realpython.com/python-print/) from this **RealPython** article.
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3. Learn more about [Basic Datatypes in Python](https://realpython.com/python-data-types/) from this **RealPython** article.
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## What's Next
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Now that you have basic knowledge of Python's core data types, we will see how we can use them to make useful output. In the next lesson, we learn about basic **math** and **comparisons**.

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