Python3-使用函数参数作为变量名

Question

I have a function that creates different forms of arrays and I don't know how to differentiate them. Is something similar to this possible?

def array_creator(nameArray):
    nameArray = [0,1,2]

array_creator(a)
print(a)  # prints [0,1,2]

At the moment I always run the function and then assign manually variables to store the arrays. Thanks!

Answer 1

For your example to work you need to define your variable a before you use it. Eg a = [] . However your example won't work the way you want to. The reason for this is that you assign a new object ( [1, 2, 3] ) to your nameArray variable in line 2. This way you lose the reference to your object a . However it is possible to change your object a from inside the function.

def array_creator(nameArray):
    nameArray.extend([0,1,2])

a = []
array_creator(a)
print(a)  # prints [0,1,2]

This will work. Have a look at How to write functions with output parameters for further information.

Answer 2

In Python you do this by returning a value from the function and binding this value to a local name, ie:

def array_creator():
    return [0, 1, 2]

a = array_creator()

Answer 3

Python does not have "output parameters", hence a plain assignment will only change the binding of the local variable, but will not modify any value, nor change bindings of variables outside the function.

However list s are mutable, so if you want to modify the argument just do so:

nameArray[:] = [0,1,2]

This will replace the contents of nameArray with 0,1,2 (works if nameArray is a list ).

An alternative is to have your function simply return the value you want to assign:

def array_creator():
    values = [0, 1, 2]
    return values

my_arr = array_creator()

Finally, if the function wants to modify a global / nonlocal variable you have to declare it as such:

a = [1,2,3]

def array_creator():
    global a
    a = [0,1,2]

print(a)   # [1,2,3]
array_creator()
print(a)   # [0,1,2]

Or:

def wrapper():
    a = [1,2,3]
    def array_creator():
        nonlocal a
        a = [0,1,2]
    return a, array_creator

a, creator = wrapper()

print(a)   # [1,2,3]
creator()
print(a)   # [0,1,2]

Note however that it is generally bad practice to use global variables in this way, so try to avoid it.