跨多个函数检查参数的优雅方式

Question

I'm working on some python code which includes a large number of functions. Many of these require the same set of input arguments.

I need to place some restrictions on the values of the input arguments. If they lie outside some prescribed range then I want to raise an error message. Ideally, I'd like to do this without lots of repeated code. Below is a simplified example of what I'm trying to do:

def check_positive(T):
    # Temperatures must be provided in kelvin
    if T < 0:
        print('Temperatures are in K, negative values not allowed!')

def double(T):
    check_positive(T)
    return 2*T

def treble(T):
    check_positive(T)
    return 3*T

T = -2
print(double(T))

T = 100
print(treble(T))

In my implementation, each function will need to call the check_positive function. Is there a more elegant way of achieving the same behavior in python?

Answer 1

Sounds like the perfect use-case for python decorators !

Edit:

from functools import wraps

def check_positive(func):
    
    @wraps(func)    
    def wrapper(*T):
        # Temperatures must be provided in kelvin
        if T[0] < 0:
            print('Temperatures are in K, negative values not allowed!')
            raise ValueError  # optional
        return func(T[0])
    return wrapper

@check_positive
def double(T):
    return 2*T

...

Answer 2

A decorator can be used here:

def check_positive(func):
    def wrapper(*args, **kw):
        if args[0] < 0:
            print('Temperatures are in K, negative values not allowed!')
        return func(*args, **kw)
    return wrapper


@check_positive
def double(T):
    return 2*T

@check_positive
def treble(T):
    return 3*T

T = -2
print(double(T))

T = 100
print(treble(T))

Output:

Temperatures are in K, negative values not allowed!
-4
300

You could change the decorator further to return an exception if a negative value was passed - here we just print the statement as in your example.