Chapter 3: Basic Decorators

Let’s build a simple decorator to time how long a function takes to execute.

Suppose we have a function that simulates a time-consuming operation:

import time

def database_operation_slow() -> None:
  """Simulates a slow database operation."""
  time.sleep(2) # Simulate work

Now, let’s create a time_it decorator

import time

def time_it(func):
  def wrapper(*args, **kwargs):
    start = time.perf_counter()
    result = func(*args, **kwargs) # Call the original function
    end = time.perf_counter()
    duration = end - start
    print(f"Function '{func.__name__}' took: {duration:.4f} seconds")
    return result
  return wrapper

# Applying the decorator
@time_it
def database_operation():
  """Simulates a database operation."""
  time.sleep(1)
  return "DB Operation Complete"

database_operation()

How it works:

time_it is our decorator. It takes a function func as input. Inside time_it, we define another function called wrapper. This function will eventually replace the original database_operation.

wrapper does three things:

• Records the time before calling the original function (func).
• Calls the original function (func(*args, **kwargs)) and stores its result. *args and **kwargs ensure our wrapper can handle any arguments the original function might take.
• Records the time after, calculates the duration, prints it, and returns the result of the original function.
• time_it returns the wrapper function.

The @time_it syntax above database_operation is Python’s syntactic sugar for: time_it(database_operation)