From Core Python Programming, 2E (3.4.1)

1. Startup line (Unix)
2. module documentation
3. module imports
4. variable declarations (Global)
5. class declarations
6. function declarations
7. “main” body

  import uuid
  uuid.uuid4()

From the official Python documentation:

Important warning: The default value is evaluated only once. This makes a difference when the default is a mutable object such as a list, dictionary, or instances of most classes. For example, the following function accumulates the arguments passed to it on subsequent calls:

def f(a, L=[]):
    L.append(a)
    return L
 
print f(1)
print f(2)
print f(3)

This will print:

[1]
[1, 2]
[1, 2, 3]

If you don’t want the default to be shared between subsequent calls, you can write the function like this instead:

def f(a, L=None):
    if L is None:
        L = []
    L.append(a)
    return L

From: Python Gotchas, Mutable defaults for function/method arguments

You should never, never, NEVER use a list or a dictionary as a default value for an argument to a class method. Unless, of course, you really, really, REALLY know what you're doing

• PEP 8 - Style Guide for Python Code ¹⁾
• Code Like a Pythonista: Idiomatic Python
• Python Coding Guidelines
• Python Coding Style & Standards

• Python Gotchas (Here or here)
• Python Pitfalls
• When Pythons Attack