# 2.5. Function#

## 2.5.1. Omit Else Clauses in a Python Function to Improve Code Readability#

If you are using if statements to return different values, adding an else clause may introduce unnecessary complexity. Omitting the else clause for the last condition will make the code simpler and easier to read.

```def get_discount(price):
if price >= 100:
return 20
if price >= 50:
return 10
else: # not necessary
return 5
```
```def get_discount(price):
if price >= 100:
return 20
if price >= 50:
return 10
return 5 # omit else
```

## 2.5.2. When to Use and Not to Use Lambda Functions#

Lambda functions are helpful when defining a function that is used only once and does not require a name.

```numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]

# use lambda function because it is used only once
even_numbers = filter(lambda num: num % 2 == 0, numbers)
```

However, if you need to reuse a function in various parts of your code, use a named function to avoid repeating the same code.

```# use named function because it is used multiple times
def is_even(num: int):
return num % 2 == 0

even_numbers = filter(is_even, numbers)
any(is_even(num) for num in numbers)
```
```True
```

## 2.5.3. How to Pass an Arbitrary Number of Arguments to a Python Function#

If you want to create a function that takes an arbitrary number of arguments, use `*args` or `**kwargs`.

`*args` allows variable arguments as a set, while `**kwargs` allows variable keyword arguments as a dictionary.

```def multiply(*nums):
print(f"nums: {nums}")
res = 1
for num in nums:
res *= num
return res

multiply(1, 2, 3)
```
```nums: (1, 2, 3)
```
```6
```
```def add_to_order(**new_order):
print(f"new_order: {new_order}")
cart = {'apple': 2, 'orange': 3}
cart.update(new_order)
return cart

```
```new_order: {'kiwi': 2, 'apple': 1}
```
```{'apple': 1, 'orange': 3, 'kiwi': 2}
```

## 2.5.4. Decorator in Python#

If you want to apply a common piece of functionality to multiple functions while keeping the code clean, use decorator. Decorator modifies the behavior of your Python functions without altering the code directly.

In the code below, `time_func` is a decorator that can be used to track the execution time of any function.

```import time

def time_func(func):
def wrapper(*args, **kwargs):
start = time.time()
func(*args, **kwargs)
end = time.time()
print(f'Elapsed time: {(end - start) * 1000:.3f}ms')
return wrapper
```
```@time_func
return num1 + num2

@time_func
def multiply(num1: int, num2: int):
print(f"Multiply {num1} and {num2}")
return num1 * num2

```Add 1 and 2