PEP 8 – Style Guide for Python Code

Import

• Place imports at the top of the file.
• Use separate lines for each import.
• Group imports in this order, with blank lines between groups:
  1. Standard library imports.
  2. Third-party imports.
  3. Local application imports.
• Avoid wildcard imports (e.g., from module import *)

Naming Conventions

Variable Names

• Style: use snake_case (lowercase letters with underscores separating words).
• Example:

  max_value = 100
  user_name = "your name"
  

• Best Practices:
  • Use _ as a prefix for private/internal variables.

Function Names:

• Style: use snake_case
• Example:

  def calculate_sum(a, b):
    return a + b
  

• Best Practices:
  • Use verbs or verb phrases to indicate the action of the function.
  • Prefix private/internal functions with an underscore (e.g., _helper_function).

Class Names:

• Style: Use CamelCase
• Example: ```python class DataProcessor: pass

class MyCustomException(Exception): pass

- **Best Practices**:
  - Use nouns or noun phrases that describe the purpose of the class.

### Constants

- **Style**: Use `ALL_CAPS` with underscores to separate words.
- **Example**:
```python
MAX_CONNECTIONS = 10
PI = 3.14159

Modules and Package Names

• Style:
  • For module (file) names: Use snake_case or short lowercase names.
  • For package names (directories): Use all lowercase, preferably without underscores.
• Example:

  file_util.py
  util/
  

Functions and Method Arguments

Default Argument Values

• Never use mutable objects (e.g., lists or dictionaries) as default values

  # Wrong example
  def append(element, target = []):
    target.append(element)
    return target
  

  The issue that the default value is evaluated only once, when the function is defined, and not each time the function is called. This can lead to unexpected behavior

  first_list = append(5)   # first_list will be [5]
  second_list = append(10) # Both first_list and second_list will be [5, 10]
  

  Here is the correct way to write this function

  def append(element, target = None):
    if target is None:
        target = []
    target.append(element)
    return target