python_code_blocks.md

Python Code Blocks and Indentation

In Python, code blocks are defined by indentation rather than by braces {} or keywords (like begin and end). This indentation rule is essential for Python syntax and structure.

Python Code Block Types

Code Block	Definition	Syntax Example	Explanation
Function Block	A block of code that defines a function.	def greet(name):	Functions start with def, followed by an indented block.
		print(f"Hello, {name}")
Class Block	A block of code that defines a class.	class MyClass:	Classes start with class, followed by an indented block.
		def method(self):
		pass
If-Else Block	A block of code that executes conditionally based on a condition.	if x > 0:	Uses if, elif, and else keywords, each followed by a colon and an indented block.
		print("Positive")
		elif x == 0:
		print("Zero")
		else:
		print("Negative")
For Loop Block	A block of code that iterates over a sequence.	for i in range(5):	The for statement is followed by an indented block.
		print(i)
While Loop Block	A block of code that repeats as long as a condition is true.	while x > 0:	The while statement is followed by an indented block.
		x -= 1
Try-Except Block	A block of code that handles exceptions (runtime errors).	try:	Begins with try, followed by one or more except blocks.
		result = 1 / x
		except ZeroDivisionError:
		print("Cannot divide by zero")
With Block	A block of code that simplifies resource management (e.g., opening files).	with open("file.txt") as f:	The with statement is followed by an indented block.
		content = f.read()
List Comprehension	A concise block for creating lists in a single line.	squares = [x**2 for x in range(10) if x % 2 == 0]	List comprehensions are single-line blocks enclosed in brackets.
Dictionary Comprehension	A concise block for creating dictionaries in a single line.	squares_dict = {x: x**2 for x in range(5)}	Dictionary comprehensions are single-line blocks enclosed in braces {}.
Docstring Block	A block of code that provides documentation for a module, class, or function.	def greet():	Docstrings are enclosed in triple quotes """.
		"""This function greets the user."""
		print("Hello")

Indentation Rules

1. Consistency: Indentation must be consistent within a block. Python allows either spaces or tabs for indentation, but not both in the same code. PEP 8 recommends using 4 spaces per indentation level.

   if x > 0:
       print("Positive")  # 4 spaces of indentation

2. Nested Blocks: Each nested block must be indented further than the previous level.

   def greet(name):
       if name:
           print(f"Hello, {name}")  # Nested block with 4 more spaces

3. Colon (:): A colon is used to start a block after statements like if, for, while, def, class, and try.

   if x > 0:  # Colon indicates the start of a block
       print("Positive")

4. Empty Blocks: Use the pass statement for empty blocks where syntax requires a statement but nothing needs to be done.

   def placeholder_function():
       pass  # Placeholder for future code

Common Indentation Errors

Error	Cause	Example	Solution
IndentationError	Mixing tabs and spaces for indentation.	if x > 0:	Use only spaces (recommended) or only tabs consistently.
		print("Positive")
Unexpected Indent	Indenting without a preceding colon or control statement.	print("Positive")	Ensure the block starts with a valid control statement or function definition.
IndentationError: Unindent	Incorrect reduction of indentation level.	if x > 0:	Ensure the indentation level matches the structure of nested blocks.
		print("End")