I understand your confusion. Let me break it down to the very basics. The core idea is that in Python, when we create a decorator that needs to pass arguments to the decorated function, we must use `*args` and `**kwargs` in both the wrapper function and when calling the decorated function within the wrapper. Here's why this is necessary.
### Why `*args` and `**kwargs` are Needed
1. **Purpose of `*args` and `**kwargs`**:
- `*args` allows the function to accept any number of positional arguments.
- `**kwargs` allows the function to accept any number of keyword arguments.
2. **Passing Arguments to the Decorated Function**:
- When you call a decorated function, the arguments you pass (like `2` and `3` in `add(2, 3)`) need to be passed through the wrapper function to the original function (`func` in this case).
- If the wrapper function does not accept `*args` and `**kwargs`, it cannot pass any arguments to `func`, which means `func(*args, **kwargs)` inside the wrapper will not work because `*args` and `**kwargs` will be undefined.
### Simplified Example Without `*args` and `**kwargs`
Here is an example that will fail to pass the arguments correctly:
```python
import time
def timer(func):
def wrapper():
start = time.time()
result = func(*args, **kwargs) # This line will cause an error
end = time.time()
return end - start, result
return wrapper
@timer
def add(a, b):
return a + b
e, r = add(2, 3) # This call will fail
print(e)
print(r)
```
In the code above, `wrapper` does not accept any arguments, so when `add(2, 3)` is called, `2` and `3` are passed directly to `wrapper`, but `wrapper` does not know what to do with them. The variables `args` and `kwargs` are not defined, leading to an error when `func(*args, **kwargs)` is executed.
### Corrected Example With `*args` and `**kwargs`
Here is the corrected version:
```python
import time
def timer(func):
def wrapper(*args, **kwargs): # Accept any arguments
start = time.time()
result = func(*args, **kwargs) # Pass arguments to the decorated function
end = time.time()
return end - start, result
return wrapper
@timer
def add(a, b):
return a + b
e, r = add(2, 3) # This call will work
print(e)
print(r)
```
### Explanation
1. **Defining the `wrapper` function with `*args, **kwargs`**:
- `def wrapper(*args, **kwargs):` allows `wrapper` to accept any number of positional and keyword arguments.
2. **Passing the arguments to `func`**:
- `func(*args, **kwargs)` calls the original `add` function with the arguments passed to `wrapper`.
3. **Calling `add(2, 3)`**:
- When you call `add(2, 3)`, it actually calls `wrapper(2, 3)`.
- `wrapper(2, 3)` calls `func(2, 3)` which is `add(2, 3)`.
By using `*args` and `**kwargs` in `wrapper`, the decorator is able to handle and correctly pass any arguments to the decorated function. This makes the decorator flexible and ensures it works with any function, regardless of the number or type of arguments it takes.