排除 `else` 会影响 Python 3 的性能吗？

Question

I was looking for an existing answer to this question, and while I came across this answer specifically about C#, this is a compiler-level thing, and so I'd expect Python might differ here.

Look at these two ways of terminating a function. First the one with the else :

if condition:
    return some_val
else:
    return some_other_val

Then the one without it:

if condition:
    return some_val
return some_other_val

Logically, the two do precisely the same thing, even if condition has side effects. They test condition , then return a value.

Is there a chance that Python 3 optimizes one over the other?

Answer 1

找出答案的一种简单方法是在循环中多次（例如 1000 万次），对两者进行计时，然后看看有什么区别。

Answer 2

If you just want to know if there's an optimization, you can use something like snakeviz to know for sure. It's difficult to give a hard and fast rule for optimization because each code brings with it different executions. For example, if you are just doing a simple x + y computation, it might give you an infinitesimally small edge not to include it, where a complex method with a variable input could cause the machine to do more work to comprehend what it's supposed to do.

From my understanding, it's considered a best practice to always include an else statement. " Explicit is better than implicit. " Always using an else statement gives a hard rule to the program of what to do in each case, it's easier to read (as your code gets more complex) and it will also help you avoid mistakes as you're going.

For an example of better readability:

variable_one = "v1"
variable_two = "v2"
if variable_one.isdigit() == False:
    if variable_one == "a":
        print("The variable is a")
    elif variable_one == "d":
        print("The variable is d")
    if variable_two == "v1":
        pass
if variable_two == "v2":
    print("variable 2 is v2")

While still pointlessly stupid, this code improves readability:

variable_one = "v1"
variable_two = "v2"
if variable_one.isdigit() == False:
    if variable_one == "a": print("The variable is a")
    elif variable_one == "d": print("The variable is d")
    else: pass

    if variable_two == "v1": pass
    else: print ("this variable was not passed")
else: pass

if variable_two == "v2": print("variable 2 is v2")
else: pass