Python中的变量函数调用

Question

I'm designing a tool which recursively identifies upstream pathways in a vector river network. I'd like to be able to truncate the search if the cumulative path cost passes a test which is defined by the user, and I'm not sure whether this is possible. Below is an example of the sort of thing I'd like to do:

def test1(value):
    if value > 1: return True
    else: return False

def test2(value):
    if value % 4: return True
    else: return False

def main(test):
    for i in range(20):
        if SPECIFIEDTEST(i):
            print i
            break

main(test1)

I know exec() can be used for this purpose but I also understand this is frowned upon? Is there another, better method for passing a function to another function?

Answer 1

You can create a dictionary that maps function names to the actual functions, and use that:

tests = {'test1': test1, 'test2': test2}
if tests[specifiedtest](i):
    ...

Answer 2

Building a dictionary for this is unnecessary, as functions can be passed in as parameters to other functions. Simply pass the function into main()

def test1(value):
    if value > 1: return True
    else: return False

def test2(value):
    if value % 4: return True
    else: return False

# using test1 as the default input value...
def main(test = test1):
    for i in range(20):
        if test(i):
            print i
            break

main(test1)
# prints 2

main(test2)
# prints 1