Code Structure and Readability¶

Readable code is easier to maintain and less likely to contain errors. Python enforces readability through indentation rules and simple syntax.

This chapter explains:

• indentation and blocks
• comments
• the pass statement

1. Indentation and Blocks¶

Unlike many languages, Python uses indentation to define code blocks.

Example:

if temperature > 30:
    print("Hot")
    print("Stay hydrated")

The colon : introduces a block, and all lines in the block must have the same indentation.

Standard indentation¶

PEP 8 recommends 4 spaces per indentation level.

Block structure¶

flowchart TD
    A[if statement]
    A --> B[indented block]
    B --> C[statement 1]
    B --> D[statement 2]

Mixing tabs and spaces can cause errors such as:

IndentationError

or

TabError

2. Nested Blocks¶

Blocks can be nested.

Example:

for i in range(3):
    for j in range(3):
        if i == j:
            print(i, j)

Each nested level increases indentation.

3. Guard Clauses¶

Guard clauses help avoid deep nesting.

Example:

def process(data):
    if data is None:
        return None

    if not validate(data):
        return None

    return transform(data)

This improves readability.

4. Comments¶

Comments are annotations ignored by the interpreter.

Example:

# This is a comment
x = 5

The most important rule:

comment why, not what.

Example:

x = 5  # server requires minimum timeout

Bad example:

x = x + 1  # increment x by 1

Comments that repeat obvious code are not useful.

5. Docstrings¶

Docstrings document functions, classes, and modules.

Example:

def calculate_area(length, width):
    """Calculate rectangle area."""
    return length * width

Docstrings are accessible at runtime:

print(calculate_area.__doc__)

6. Comment Markers¶

Common markers include:

TODO
FIXME
HACK
NOTE

Example:

# TODO: optimize algorithm
# FIXME: handle empty list

7. The pass Statement¶

Python requires every block to contain at least one statement.

The pass statement acts as a placeholder.

Example:

def future_feature():
    pass

Example class:

class DatabaseConnection:
    pass

pass performs no operation but satisfies the syntax requirement.

8. pass vs Ellipsis¶

Python also provides the ellipsis literal:

...

Example:

def parse():
    ...

Both serve as placeholders.

9. pass Does Not Exit a Function¶

Example:

def demo():
    pass
    print("Still runs")

demo()

Output:

Still runs

Unlike return, pass does not stop execution.

10. Summary¶

Key ideas:

• indentation defines program structure
• blocks follow a colon :
• comments explain intent
• docstrings document functions and modules
• pass creates intentionally empty blocks

These conventions help Python code remain clear and readable.