Using functions as input

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)
   ...

show us the import statement, but it sounds like you're trying to turn strings into python commands, which is a Bad Thing to do. Show us also how you're calling A (from terminal, I assume?) — Adam Smith
– Adam Smith, Commented Jan 25, 2015 at 3:38
I'm also calling A from idle. I press f5 to run the program, which runs without errors, then try A(f1, f2, f3, f4) and get the error I posted above — mdegges
– mdegges, Commented Jan 25, 2015 at 3:43
Actually the code snippet from your function body looks rather strange, can you post the entire function definition? — zehnpaard
– zehnpaard, Commented Jan 25, 2015 at 3:44
Sure, I updated my post. I'm trying to plot points using the results from calling user-specified functions in (B) on a range of inputs. — mdegges
– mdegges, Commented Jan 25, 2015 at 3:51

zehnpaard · Accepted Answer · 2015-01-25 04:10:49Z

2

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

edited Jan 25, 2015 at 4:10

answered Jan 25, 2015 at 3:42

zehnpaard

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3 Comments

mdegges Over a year ago

Will the alt import the actual f1, f2, f3, and f4 functions from B, or will it import the functions the user specifies when they run the program, using A(f62, f22, f2323, f100)?

zehnpaard Over a year ago

it will be whatever they specify. Let me rewrite the code to make it clearer.

Adam Smith Over a year ago

inside A, it'll use the local f1 f2 f3 and f4. Outside it'll use the imported ones. Name them something else to prevent confusion.

Anzel · Accepted Answer · 2015-01-25 04:06:36Z

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.

Adam Smith · Accepted Answer · 2015-01-25 04:09:04Z

0

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)

answered Jan 25, 2015 at 4:09

Adam Smith

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