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 double underscore) 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.

Branislav Dev Blog

Branislav Dev Blog

Variables and Strings