函数返回返回int或int列表。 将第一个与变量相关联

Question

Suppose we have

def f_1():
    return (3, 4)

def f_2():
    return 2

The functions are given. It is not code that I can modify. We know they return either an integer or a sequence of them.

I would like to assign the return to a variable, where the variable should take only the first of the integers if the return is a sequence of them.

Is there a build-in syntactic device in Python that allows me to do this?

for function in [f_1, f_2]:
    ...
    x = function()[0] # Works for f_1, breaks for f_2
    y = function()    # Works for f_2, assigns (3, 4) for f_1 while 
                      #   we really would like only the 3 to be the 
                      #   assigned value

Note: Assume that we don't know which of the functions return the sequence and which return just a number.

Answer 1

Is there a build-in syntactic device

No. The usual practice is to ask for forgivness :

x = function()
try:
    x = x[0]
except TypeError:
    pass

Answer 2

I wouldnt go for try-except statement. To me it's an overkill.

More likely I would try to do something like:

result = function()
# this can be changed to abc.Sequence for more general approach
if isinstance(result, (list, tuple)): 
    result = result[0]

Answer 3

Going in the other direction, wrap f_2 in another function to ensure that the function called in the body of the loop always returns a sequence.

for function in [f_1, lambda : (f_2(),)]:
    x = function()[0]

The additional overhead of another function call may make this approach undesirable.