Python Syntax Basics

📘 Key Concepts and Definitions

• Variable: A named location used to store data in memory.
• Data Type: A category for values. Common types include str (string), int (integer), float (decimal), bool (boolean), list, and dict (dictionary).
• Indentation: Python uses whitespace (spaces or tabs) to define code blocks, instead of braces {}. This is a core part of the syntax.
• Function: A reusable block of code that performs a specific task. Defined with the def keyword.
• Module: A file containing Python code. You can import modules to use their functions and variables in other files.
• PEP 8: The official style guide for Python code, which provides conventions for readability and consistency.

🧮 Code Block Structure

Python's structure is defined by colons : and indentation. A block of code starts after a colon and is indented.

Function Structure

def function_name(parameter1, parameter2):
    # This block is indented
    result = parameter1 + parameter2
    return result

Conditional Structure

if condition1:
    # Do something if condition1 is true
elif condition2:
    # Do something if condition2 is true
else:
    # Do something if no conditions are true

🛠️ Core Syntax Reference

Variables and Data Types

# No type declaration needed
name = "Alice"      # str
age = 30            # int
height = 5.5        # float
is_student = True   # bool

Common Data Structures

# List (ordered, mutable)
my_list = [1, "apple", 3.14]

# Tuple (ordered, immutable)
my_tuple = (1, "apple", 3.14)

# Dictionary (unordered, key-value pairs)
my_dict = {"name": "Bob", "age": 25}

# Set (unordered, unique elements)
my_set = {1, 2, 3, 3, 4} # Becomes {1, 2, 3, 4}

Operators

• Arithmetic: +, -, *, / (division), // (floor division), % (modulus), ** (exponent).
• Comparison: ==, !=, >, <, >=, <=.
• Logical: and, or, not.

Control Flow

# For loop
for item in my_list:
    print(item)

# While loop
count = 0
while count < 5:
    print(count)
    count += 1

String Formatting (f-strings)

name = "Charlie"
age = 40
print(f"My name is {name} and I am {age} years old.")
# Output: My name is Charlie and I am 40 years old.

🧭 Basic Scripting Workflow

1. Import necessary modules at the top of your file (e.g., import os).
2. Define functions to encapsulate reusable logic.
3. Initialize variables to hold state or data.
4. Write the main logic of your script. This might involve loops, conditionals, and function calls.
5. Use a main block to make your script reusable as a module:

   if __name__ == "__main__":
       # Your main script execution code goes here
       pass
   

⌨️ Productivity Tips

• List Comprehensions: A concise way to create lists.

  # Traditional way
  squares = []
  for i in range(5):
      squares.append(i * i)
  
  # Comprehension way
  squares = [i * i for i in range(5)] # [0, 1, 4, 9, 16]

• Virtual Environments: Always use a virtual environment (e.g., `venv`) to manage project dependencies and avoid conflicts.

  python -m venv myenv
  source myenv/bin/activate  # On Linux/macOS

• Linters and Formatters: Use tools like flake8 (linter) and black (formatter) in your editor to automatically enforce PEP 8 and keep your code clean.

📊 Data Type Overview

🧪 Example: Word Count Script

A simple script to count the frequency of words in a given text.

def count_words(text):
    """Counts the frequency of each word in a string."""
    word_counts = {}
    words = text.lower().split() # Lowercase and split into words

    for word in words:
        # Remove punctuation for better counting
        cleaned_word = word.strip(".,!?")
        if cleaned_word:
            word_counts[cleaned_word] = word_counts.get(cleaned_word, 0) + 1
    
    return word_counts

if __name__ == "__main__":
    sample_text = "Hello world! This is a test. Hello again."
    counts = count_words(sample_text)
    print("Word frequencies:")
    for word, count in counts.items():
        print(f"- {word}: {count}")

🧹 Troubleshooting Common Errors

• Error: IndentationError: expected an indented block
  • Fix: This is the most common Python error. The line after a : (like in an if, for, or def statement) must be indented. Ensure consistent use of spaces (PEP 8 recommends 4).
• Error: SyntaxError: invalid syntax
  • Fix: You have a typo. Look for missing colons :, mismatched parentheses () or brackets [], or an illegal character.
• Error: NameError: name '...' is not defined
  • Fix: You're trying to use a variable or function that hasn't been created yet. Check for typos in the variable name or make sure it's assigned before being used.
• Error: TypeError: can only concatenate str (not "int") to str
  • Fix: You are trying to combine different data types, like "Score: " + 10. Convert the non-string type using str(): "Score: " + str(10). Or better yet, use an f-string: f"Score: {10}".

📚 References and Further Reading

• Official Python Documentation: The Python Tutorial
• PEP 8 Style Guide: PEP 8 -- Style Guide for Python Code
• Real Python: In-depth articles and tutorials
• Automate the Boring Stuff with Python: A practical, free online book for beginners.