使用函数作为输入

Question

I've written a program (A) that takes, as input, the names of functions I wrote in a separate program (B). I want to use these functions in program (A), so I am trying to run (A) by doing this: A(f1, f2, f3, f4)

At the top of (A), I imported program (B) using import B. In (A) there is just one function (excluding main) that accepts four inputs (f1, f2, f3, f4), and then uses them, like this:

    for i in range(x, y):
       z = B.f1(i)
       u = B.f2(i)
       ...
    ...

The trouble is, when I try to run A(f1, f2, f3, f4), I get the error

Traceback (most recent call last):
   File "<pyshell#0>", line 1, in <module>
      A(f1, f2, f3, f4)
NameError: name 'f1' is not defined

I see that python is not recognizing the functions in (B) as input in (A), but I don't know why or how else I can connect the two programs.

Update: Program A

def A(f1, f2, f3, f4) :

   x = 0
   y = 10

   for i in range(x, y):
       x = B.f1(i) //returns float
       plt.plot(i, x)
   ... 

Answer 1

Based on a literal reading of your question, if you imported B via

import B

then every reference to functions, variables, classes etc defined in B must be done in the form B.func1 etc.

Your error message clearly says that you're trying to do A(f1, f2, f3, f4) . This should be A(B.f1, B.f2, B.f3, B.f4)

EDIT Judging from your updated question, I'm guessing you want something like:

import B

def A(input_function1, input_function2, input_function3, input_function4) :
    x = 0
    y = 10

    for i in range(x, y): #btw, you don't need the x value here if it's 0
        x = input_function1(i) //returns float #I removed the 'B.'
        plt.plot(i, x)
    # Other stuff here

if __name__=='__main__':
    A(B.f1, B.f2, B.f3, B.f4)
    # or alternatively A(B.f78, B.f21, B.f1, B.f90) or whatever

Or alternatively:

from B import f1, f2, f3, f4

def A(f1, f2, f3, f4) :
    # Stuff here

if __name__=='__main__':
    A(f1, f2, f3, f4) # Explicit imports mean that the 'B.' prefix is unnecessary

Answer 2

To extend what @zehnpaard has already suggested, if you want to call the B function in A() using f1...f4 as arguments, you can alternatively use getattr() , like this:

...
def A(f1, f2, f3, f4) :

   x = 0
   y = 10

   for i in range(x, y):
       x = getattr(B, f1)(i)
       plt.plot(i, x)
   ... 

getattr(B, f1) will return the function as in B.f1 , and you call the function and pass the argument i with (i) , just like: getattr(module, function)(*args) .

For example: getattr(plt, 'plot')(i, x) = plt.plot(i, x)

Pay attention that you pass plot as string 'plot' , so when you're trying to call function A() , you will do:

if __name__=='__main__':
    A('f62', 'f22', 'f2323', 'f100')

As a side note: if the function you pass is not in B , it will raise AttributeError .

Hope this helps.

Answer 3

Sounds like you have the following defined in your interactive session

import B

def A(f1, f2, f3, f4):

    for i in range(10):
        plt.plot(i, f1(i))

And the user should call it by doing:

>>> A(B.f1, B.f49, B.f100, B.f42)