---
title: Python Basics
description: The basics of python. We all need to start somewhere, so how about doing it here.
---
## Variables
You can name a variable anything as long as it obeys the following rules:
1. It can be only one word.
```python
>>> # this wont work
>>> my variable = 'Hello'
>>> # good
>>> var = 'Hello'
```
2. It can use only letters (A-z), numbers(0-9), and the underscore (`_`) character.
```python
>>> # this wont work
>>> %$@variable = 'Hello'
>>> # good
>>> my_var = 'Hello'
>>> # good
>>> my_var_2 = 'Hello'
```
3. It can’t begin with a number.
```python
>>> # this wont work
>>> 23_var = 'hello'
```
4. Do not use keywords or built-in function as the variable name
```python
>>> # this wont work
>>> if = 'hello'
>>> # this is bad
>>> print = 'world'
```
## Data Types
| Data Type | Examples |
| ---------------------- | ----------------------------------------- |
| Bool | `True`, `False` |
| Integers | `-2, -1, 0, 1, 2, 3, 4, 5` |
| Floating-point numbers | `-1.25, -1.0, --0.5, 0.0, 0.5, 1.0, 1.25` |
| Complex numbers | `2+1j`, `3-5j` |
| Strings | `'a', 'aa', 'aaa', 'Hello!', '11 cats'` |
:::info
:bulb: Use the built-in function `type()` to verify the datatype of the value assigned to a variable.
:::
## Math Operators
From **Highest** to **Lowest** precedence:
| Operators | Operation | Example |
| --------- | -------------------------| --------------- |
| \*\* | Exponent | `2 ** 3 = 8` |
| % | Modulus/Remainder | `22 % 8 = 6` |
| // | Floor(Integer) division | `22 // 8 = 2` |
| / | Float(True) Division | `22 / 8 = 2.75` |
| \* | Multiplication | `3 * 3 = 9` |
| - | Subtraction | `5 - 2 = 3` |
| + | Addition | `2 + 2 = 4` |
| >>, << | shifting | `16 >> 2 ` |
| &,^, \| | bitwise-logical operator | `1^0 ` |
| >,>=,== | Comparison operator | `2!=3 ` |
| not, and, or | Logical operator | `(4 < 5) and (5 < 6)` |
| =,+=,*= | assignment symbol | `a +=1` |
:::info
:bulb: You can use parenthesis to properly specify the order of operations in complex expressions.
:::
Examples of expressions:
```python
>>> 2 + 3 * 6
# 20
>>> (2 + 3) * 6
# 30
>>> 2 ** 8
#256
>>> 10 / 2
#5.0
>>> -11 / 2
#-5.5
>>> 23 // 7
# 3
>>> -5.0 // 2
# -3.0
>>> 23 % 7
# 2
>>> (5 - 1) * ((7 + 1) / (3 - 1))
# 16.0
```
## Augmented Assignment Operators
| Operator | Equivalent |
| ---------- | --------------- |
| `var += 1` | `var = var + 1` |
| `var -= 1` | `var = var - 1` |
| `var *= 1` | `var = var * 1` |
| `var /= 1` | `var = var / 1` |
| `var %= 1` | `var = var % 1` |
| `var **= 2`| `var = var**2` |
Examples:
```python
>>> greeting = 'Hello'
>>> greeting += ' world!'
>>> greeting
# 'Hello world!'
>>> number = 1
>>> number += 1
>>> number
# 2
```
## Multiple assignment
```python=
my_string = 'characters'
my_Boolean = True # True/False
my_integer = 5
my_floating_point = 26.2
my_complex = 2+1j # Note that 1 can not be omitted
# The above code is equivalent to
my_string, my_Boolean, my_integer, my_floating_point, my_complex = 'characters', True, 5, 26.2, 2+1j
```
```
```
## String concatenation and Replication
String concatenation:
```python
>>> 'Alice' + 'Bob'
# 'AliceBob'
```
String Replication:
```python
>>> 'Alice' * 5
# 'AliceAliceAliceAliceAlice'
```
## Comments
Inline comment:
```python
# This is a comment
```
Multiline comment:
```python
# This is a
# multiline comment
```
Code with a comment:
```python
a = 1 # initialization
```
Function docstring or multiline comments can also be used:
```python
"""
This is a function docstring
You can also use it as multiline string
"""
```
## The `print()` Function
The `print()` function writes the value of the argument(s) it is given. It handles multiple arguments, floating point-quantities, and strings. Strings are printed without quotes, and a space is inserted between items, so you can format things nicely:
```python
>>> print('Hello world!')
# Hello world!
>>> a = 1
>>> print('Hello world!', a)
# Hello world! 1
>>> print('Hello,\
World') # It is possible for statements to span more than one line using `\`
# Hello, World
```
### The escape sequence
```python=
>>> print("Welcome\nto\nthe course")
#Welcome
#to
#the course
```
### The end keyword
The keyword argument `end` can be used to avoid the newline after the output, or end the output with a different string:
```python
print("Welcome", end='-')
print("to the course")
...
# Welcome-to the course
```
### The sep keyword
The keyword `sep` specify how to separate the objects, if there is more than one, the default value is a white space:
```python
print('cats', 'dogs', 'mice', sep=',')
# cats,dogs,mice
```
## The `input()` Function
This function takes the input from the user and converts it into a string:
```python
>>> print('What is your name?') # ask for their name
>>> my_name = input()
>>> print('Hi' + my_name)
# What is your name?
# Martha
# Hi, Martha
```
`input()` can also set a default message without using `print()`:
```python
>>> my_name = input('What is your name? ') # default message
>>> print('Hi' + my_name)
# What is your name? Martha
# Hi, Martha
```
## The `len()` Function
Evaluates to the integer value of the number of characters in a string, list, dictionary, etc.:
```python
>>> len('hello')
# 5
```
## The `bool()`, `int()`, `float()`, `complex()` and `str()` Functions
These functions allow you to change the type of variable. For example, you can transform from an `integer` or `float` to a `string`:
```python
>>> str(29)
# '29'
>>> str(-3.14)
# '-3.14'
```
Or from a `string` to an `integer` or `float`:
```python
>>> int('11')
# 11
>>> float('3.14')
# 3.14
```
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