Python: Basic Concepts

Python Basic Concepts

python
basic-concepts
Python Basic Concepts
Author

Isaac Boixaderas

Published

Sunday, June 1, 2025

Modified

Tuesday, October 14, 2025

1 Overview

📘 Python

Python is a high-level, interpreted programming language known for its simplicity and readability. Created by Guido van Rossum and first released in 1991, Python emphasizes code readability with its use of significant indentation. It supports multiple programming paradigms including procedural, object-oriented, and functional programming. Python is widely used in web development, data science, artificial intelligence, automation, and scientific computing.

2 Main Programming and Python Concepts

3 Displaying text

print() built-in function:

  • Writes text to the console (or standard output).
  • Takes multiple arguments (between the parentheses) and displays them.
print(3.1416)
3.1416 
print("Hello world!")
Hello world!
  • By default, print adds a new line at the end of the string.
print("Hello world!")
print("This is a new line.")
Hello world!
This is a new line.
  • If values separated by commas, print automatically adds a space in between.
print("Hello", "world!", "How are you?")
Hello world! How are you?

4 Comments

  • Code lines are executed from top to bottom.
  • Empty lines do nothing.
  • Comments are lines of text in between your code that are not executed.
  • Used for providing explanations, notes, descriptions…
  • 2 types:
    • Single-line (#)
    • Multi-line comments (enclosing text in ''' or """)
# This is a single-line comment
print("Hello, world!")  # This is an inline comment

# print(2 + 3)
# The code above is commented out, so it won't be executed
print(5 + 5)  # This line before this comment will be executed
Hello, world!
10 
"""
This is a multi-line comment.
You can write explanations or descriptions
that span multiple lines.
"""
print("Hello, world!")
Hello, world!

5 Number operations

print(2 + 3)   # addition (+)
5 
print(3 - 1)   # subtraction (-)
2 
print(2 * 3)   # multiplication (*)
6 
print(3 / 2)   # division (/)
1.5 
print(3 // 2)  # floor division (//)
1 
print(3 ** 2)  # exponential (**)
9 
print(3 % 2)   # modulus (%)
1

6 Data types

  • Categories of values that share characteristics.
  • Dictate how values are stored, represented…
  • type() built-in function:
type(2)
[‘int’] 
type(2.5)
[‘float’] 
# string
type('Hello world!')
[‘str’]

6.1 Built-in types

Built-in types

Built-in types

Different types have different properties on how they interact between them:

5 - 1
4 
'a' - 'b'
TypeError: unsupported operand type(s) for +: ‘int’ and ‘str’ 
5 + 1
6 
'a' + 'b'
‘ab’ 
# Take care, this is a string!
'5' + '1'
‘51’ 
# Cannot mix types
5 + 'a'
TypeError: unsupported operand type(s) for +: ‘int’ and ‘str’

7 Casting

  • Converting one type to another.
  • Using built-in functions int(), float(), str(), etc.
# Type is string when a number is in quotes
print(type('1'))
<class ‘str’> 
# But we can convert it to integer by using the int() function
print(type(int('1')))
<class ‘int’> 
# After converting the string to integer, we can operate on it
print(3 + int('1'))
4 
# We can also do it the other way and transform an integer to a string
print(type(1))
print(type(str(1)))
<class ‘int’>
<class ‘str’> 
# After converting the integer to string, we can operate on it
print('abc' + str(1))
print('5' + str(1))
abc1
51 
# Take care when converting floats to integers, as the decimal part will be removed
print(int(3.14))
print(int(3.99))
3
3

8 Variables

  • Used for storing and manipulating data.
  • Naming:
    • Should start with a letter a-z or A-Z or an underscore (_).
    • They can also contain numbers, as long as a number is not the first character.
    • Case-sensitive.
  • Assignation
    • With =
    • No need to specify data type (done automatically by Python).
    • Reassignation is allowed at any time.
# Variable assignation examples:

name = 'John Doe'
age = 25
is_student = True
  • Python automatically detects the data type based on the assigned value:
print(type(name))
print(type(age))
print(type(is_student))
<class ‘str’>
<class ‘int’>
<class ‘bool’>
  • Use the value of the variables anywhere in the program:
print(name)
John Doe 
print(age)
25 
# You can also change the value of the variable,
# so its value will be overwritten.
name = 'Isaac'
print(name)
Isaac
  • We can operate with variables as if they were the values:
number1 = 1
number2 = 2

print(number1 + number2)
3 
print(number1 - number2)
-1 
surname = 'Newton'

# Arguments in `print()` are automatically separated by a space.
print(name, surname)
Isaac Newton 
# With +, words are concatenated.
print(name + surname)
IsaacNewton

8.1 Updating operation

  • For updating the value of a variable, we can do it in the classical way:
x = 5

# Add 1 to x
x = x + 1
print(x)
6
  • Shortcut for updating a variable:
x = 5

# Add 1 to x
x += 1
print(x)
6 
# Subtract 2 from x
x -= 2  # This is equivalent to x = x - 2
print(x)
4 
# Multiply x by 3
x *= 3  # This is equivalent to x = x * 3
print(x)
12 
# Divide x by 4
x //= 4  # This is equivalent to x = x // 4
print(x)
3

8.2 Convention variable names

  • Snake Case: Words separated by _. E.g., is_student, user_name or name_and_surname.
  • Camel Case:
    • Lower Camel Case: First word lowercase, subsequent words start with capital letter. E.g., isStudent, userName, nameAndSurname.
    • Upper Camel Case (Pascal Case): First word also capitalized. E.g., IsStudent, UserName, NameAndSurname.

9 Keywords

  • Python’s reserved words. They have a special purpose and functionality and cannot be used as identifiers (variable names, function names, class names, etc.).
and del from not as
elif global or assert else
if pass async except import
raise await finally in return
break for is try class
with lambda while continue yield
nonlocal def False None True 
# We get an error if we try to use 'break' as a variable name
break = 3
SyntaxError: invalid syntax 
# But we can use variations
breac = 3
print(breac)
3

10 Built-in functions

  • Built-in functions are globally available in any Python program.
  • Unlike reserved words, it is possible to use built-in function names as variable names, thus modifying the default behavior (NOT RECOMENDED!).
abs all any ascii bin
bool breakpoint bytearray bytes callable
chr classmethod compile complex delattr
dict dir divmod enumerate eval
exec filter float format frozenset
getattr globals hasattr hash help
hex id input int isinstance
issubclass iter len list locals
map max memoryview min next
object oct open ord pow
print property range repr reversed
round set setattr slice sorted
staticmethod str sum super tuple
type vars zip import
  • Take care!
print = 5
a = print + 2   # `a` has the value 7
print('Hello')  # Error because `print` is now the value 5
TypeError: ‘int’ object is not callable

11 User input

  • Reads text from the user.
  • Returns it as a string.
name = input('Enter your name: ')
print(name)
Enter your name: Isaac
Isaac 
# Take care because it returns a string
age = input('Enter your age: ')
print(age + 1)
TypeError: can only concatenate str (not “int”) to str 
# This code works well, as we parse the input to an integer
age = int(input('Enter your age: '))
print(age + 1)
32

12 Example

Write a program in which a user enters his/her name and age and the system prints a message with that information.

# Use input for processing the user name
user_name = input('Enter your name: ')
# Use input for processing the user age
user_age = int(input('Enter your age: '))

# Remember that, by default, the input function returns a string,
# so we do not need to convert the age to integer for concatenating it
print('Hello! You are ', user_name, ' and you are ', user_age, ' years old.')
Hello! You are Isaac and you are 31 years old.
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