Python Basics

Python is a high-level general purpose language. This lesson will cover some of the basic language design philosophies as well as common mistakes.

Python Philosophy

Python was designed with a philosophy that emphasizes code readability and simplicity. The core principles are captured in "The Zen of Python" by Tim Peters, which you can view by running:

import this

Key principles include:

• Simple is better than complex
• Readability counts
• Explicit is better than implicit
• Flat is better than nested

Python Versions

Python has two major versions in use today:

• Python 3.x (current and recommended) - All examples in this course use Python 3
• Python 2.x (legacy, support ended January 2020)

Always check which version you're using by running:

import sys
print(sys.version)

Running Python Code

There are several ways to run Python code:

1. Interactive Mode (REPL): Open a terminal and type python to start the Python interpreter
2. Script Mode: Create a file with a .py extension and run it with python filename.py
3. IDEs and Code Editors: Tools like VS Code, PyCharm, or Jupyter Notebooks

Comments in Python

Comments are important for documenting your code. Python uses the # symbol for single-line comments:

# This is a comment
print("Hello, World!")  # This is an inline comment

For multi-line comments, you can use triple quotes (when placed before a module, class, function_a, etc these are known as docstrings_b):

"""
This is a multi-line comment.
You can write as many lines as you want.
It's useful for longer explanations.
"""

Indentation Matters

Unlike many programming languages that use braces {} (such as C, Javascript, etc) to define blocks_c of code, Python uses indentation:

if True:
    print("Indented code belongs to the if block")
    print("This is also in the if block")
print("This is outside the if block")

Good Practice:

• Use 4 spaces for each level of indentation (PEP 8 recommendation)
• Be consistent with your indentation

Bad Practice:

if True:
  print("Using 2 spaces")
    print("Then using 4 spaces")  # This will cause an IndentationError

Why it's Bad: Inconsistent indentation will cause errors and make your code hard to read.

Your First Python Program

The traditional first program in any language is "Hello, World!":

print("Hello, World!")

Let's analyze this simple program:

• print() is a built-in function that displays output
• The text inside the parentheses is a string (enclosed in quotes)

Common Mistakes for Beginners

1. Incorrect Indentation:

   # Bad
   if True:
   print("This will cause an error")
   
   # Good
   if True:
       print("Properly indented")

2. Forgetting Colons:

   # Bad
   if True
       print("Missing colon after condition")
   
   # Good
   if True:
       print("Colon included")

3. Mixing Tabs and Spaces:

   # Bad (mixing tabs and spaces - hard to show in text)
   if True:
       print("Indented with spaces")
   	print("Indented with a tab")
   
   # Good
   if True:
       print("Consistent indentation")
       print("Still using spaces")

4. Case Sensitivity Issues:

   # Bad
   Print("Python is case-sensitive")  # 'Print' is not recognized
   
   # Good
   print("Correct function name")

Although python is a beginner friendly language, attention to detail is important.

Definitions

a - A function is a reusable block of code that performs a specific task.
b - A docstring is a string, usually a comment, used to document a piece of code
c - A block of code is a group of programming statements combined into a group. Everything within this group is executed together.