Python tutorial 1 – Variables & Data Types

The 1st thing to know is that all Python files end with the extension .py. Then you have to understand that every programming language must have the ability to Accept, Store and Name Data.

You have to be able to receive data from the keyboard, or from other parts of your program and assign a name to that data. This data is either a single value or multiple values that are assigned a name. Data that is assigned a name and that contains data is called a Variable. Python has many different ways to store lists of data which I’ll cover later.

It is convenient to assign names to data. If I want to store my age in Python I’d type my_age = 43. If I wanted to store my name I’d type my_name = “Sohan”.

Rules for Naming Variables

  • Your variables can start with a letter or _ (Underscore)
  • After the 1st letter, you can use numbers such as num_1
  • You can’t put spaces in variable names my_age is ok, but my age is not
  • It is considered a good practice to separate words with underscores (my_age vs. myAge)
  • Keywords that you can’t us for variable names
  • and, del, from, not, while, as, elif, global, or, with, assert, else, if, pass, yield, break, except, import, print, class, exec, in, raise, continue, finally, is, return, def, for, lambda, try

Try running this code where you assign your name to a variable and then print a message.

my_name = “Sohan”
print(“Hello”, my_name)

“Hello” is known as a string. The print() function prints out your screen the values between
its parentheses. If you have multiple values separate them with commas.

Data is stored in essentially boxes in your computer’s memory. The size of the box you assign is
referred to as a data type. If you want to store values with decimal places you store that data in
a float data type. If you want to store a series of characters, numbers, etc. you store in a string
data type.

Strings

A String is a data type that starts and ends with a “ ‘ or ‘’’ and contains letters, numbers and
other characters. If you find that you want to use a double quote inside of a String proceed it
with a backslash like this.

print(“\”We never really grow up, we only learn how to act in public\” - Bryan White”)

Escape Sequences

\” is one of many Escape Sequences. Here are other common Escape Sequences

  • Newline : \n
  • Backslash : \\
  • Single Quote : \’
  • Backspace : \b
  • Tab : \t

I’ll do more with Strings later in the tutorial.

Number Data Types

There are 3 main types in Python. Integers, floats and complex numbers. I’ll cover
complex numbers later.

Integers are values that don’t have decimal values. 3, 8, 100000 are integers. Floats contain
decimal values. Pi, for example, is a float.

There is no maximum value for an integer, as long as you have enough memory. You can, however, get a practical maximum size with this. Note that you’ll have to import the sys module
for this code to work. A module provides a prewritten code you can use in your program.

import sys
print(sys.maxsize)

You can get the maximum size for a float like this

import sys
print(sys.float_info.max)

Please note however that errors can occur when using floats. This is true with all programming
languages. When you create a variable a specific amount of space is set aside. If you create a
value larger then that space allows errors can creep in. For example

f1 = 1.1111111111111111
f2 = 1.1111111111111111
f3 = f1 + f2
print(f3)

As you can see floats are accurate to 15 digits. Later I’ll introduce data types with more
accuracy.

Here is an example of a complex number. I’ll cover them in more detail later.

Cn1 = 5 + 6j

Booleans

A boolean data type can have either a value of True or False. You’ll see how extremely valuable
they are later.

can_vote = True

Dynamic Typing

Python is dynamically typed. What that means is a variables data type is determined by the
value you assign to it. This is different from other languages. A variable’s value can also be
changed even if that may sometimes not make sense. For example

my_age = 43
my_age = “Dog”

Many errors can occur if you don’t make sure you are using the correct values. Some times you
will find the need to convert from one type to another.

Casting

Casting allows you to convert from one type to another. Here is how you cast to the different
types. I’ll use the type() function to display the new data type for each variable.

print("Cast ", type(int(5.4))) # float to int
print("Cast 2 ", type(str(5.4))) # float to string
print("Cast 3 ", type(chr(97))) # unicode character to string
print("Cast 4 ", type(ord('a'))) # character to unicode
print("Cast 5 ", type(float(2))) # integer to float

Commenting

You may have noticed the # symbol used in the code above. # is used when you want to
comment about what your code is doing. Everything you type after a # is ignored. It is very
important to comment on your code because what you understand about your code today you
may forget 3 months from now.

You can also create multi-line comments like this

‘’’
I’m a multi-line comment
‘’’

Common Variable Errors

Variable names are case sensitive. For example Age is not the same as age.

Age = 2
Age = 3

Make sure you are casting to the correct data type when working with variables. Also, make
sure that you surround calculations with parentheses when they produce a single value.

num_1 = “1”
num_2 = “2”
print(“1 + 2 =“, (int(num_1) + int(num_2)))

That’s all for now. Next, we’ll learn about accepting user input and performing math calculations.