# Variables and Strings

In another blog post from my learning progress we will cover **Variables** and **Strings** in Python.



> What are variables ?

*From my understanding variable is something that holds a value assigned to it.*



**In Python you can name your variables whatever you want but with some restrictions.**


- Variables must start with letter or underscore

```
# correct
_name
age

#wrong
2names
``` 

- The rest of the name must consist of letters, numbers, or underscores


```
# correct
cats2

#wrong
hey@hey

``` 

- Names are case sensitive

```
CATS != Cats 

Cats != cats

``` 




**Naming conventions **



- snake_case (underscore between words)

```
first_name

``` 

- lowercase, with some exceptions 

***CAPITAL_SNAKE_CASE*** usually reffers to constants eg. 

```
PI = 3.14
``` 

- UpperCamelCase usually reffers to a class

- Variables that start and end with two underscores (called "dunder" for **d**ouble **under**score) are supposed to be private or left alone


```
__leave_me_alone__
``` 


**Dynamic typing**


> Python is highly flexible about reasigning to different types

Example: 


```
awesomeness = True
print(awesomeness) # True

awesomeness = "a dog"
print(awesomeness) # a dog
``` 

In this example you can see in 1 line that we assigned boolean value to awesomeness variable and later on line 4 we assigned a string value of "a dog" to awesomeness variable



> In C++ this will result in error as C++ is **Static Typed** that means it has to stay with type that was original assigned to it

```
# integer
int not_awesomeness = 3;

# string
awesomeness = "cool" # !Error
``` 



** Special value *None* **

Value "None" represents nothing. If you're experienced with other programming languages such as Javascript or PHP the Python value "None" is equals to the "null" value in JS or PHP.




**String Concatenation**


>In Python we can connect or join strings together (as many as you want).

We would like to do it with "+" a plus sign.

Example:

```
first_name = "Branislav"
last_name = "Buna"

print(first_name + last_name) # BranislavBuna

# in case we would like to add space between those strings 
print(first_name + " " + last_name) # Branislav Buna

# or include something else than space

print("First name: "first_name + " and " + "Last name: "+ last_name)
# First name: Branislav and Last name: Buna
``` 





**String formating**


> There're several methods  to format strings in Python to interpolate variables.


- The new way (in Python 3.6+) => F. strings

```
x = 10

formated = f"I've told you {x} times already"

# I've told you 10 times already
``` 


- The tried-and-true way (in Python 2 -> 3.5) => .format method

```
formated = "I've told you {} times already".format(10)

# I've told you 10 times already
``` 




**String indexes**

>Anytime we would like to access the particular character index/position in the given string we might look on this method.

Example:


```
str = "hello"
str[0] # h
``` 

You might me asking why we started with 0 ?
Well it is because in programming we call it **Zero-based numbering**


```
str = "hello" # 0 = h , 1 = e, l = 2 , l = 3, o = 4
str[0] # h

# we can also ask for character with negative number this will give us ability to go from the back of the string

str[-1] # o
``` 




Well that might be it today, I hope you will enjoy.