How to call a function from a list?

Question

For example, I have the following list:

method = [fun1, fun2, fun3, fun4]

Then I show a menu where the user must select a number from 1-4 (len(method)). If the user selects i, I have to use the function funi. How can I do that?

Eg.

A=['hello','bye','goodbye']
def hello(n):
 print n**2
def bye(n):
 print n**3
def goodbye(n):
 print n**4

If I want to call the function bye by the array A, using

>>>A[1](7)
Traceback (most recent call last):
File "<pyshell#0>", line 1, in <module>
A[2](5)
TypeError: 'str' object is not callable

How can I use the names saved in A to call my functions? because every method is saved in a string.

Do you mean funi = method[i-1] (indices are zero-based in Python)? Perhaps try reading a Python tutorial on lists? — jonrsharpe
– jonrsharpe, Commented May 31, 2015 at 21:09
yes, I just need the way to call the method, the index is easy to fix, thanks ! — luisfelipe18
– luisfelipe18, Commented May 31, 2015 at 21:21
Why are you storing strings in the list, rather than the functions themselves (A = [hello, bye, goodbye])? — jonrsharpe
– jonrsharpe, Commented May 31, 2015 at 21:38
Use A=[hello, bye, goodbye] instead. In this way, you store the methods, not their names. And then you can use them like A[1](17) — matiasg
– matiasg, Commented May 31, 2015 at 21:39

Tasos Vogiatzoglou · Accepted Answer · 2015-05-31 21:45:39Z

8

Let's see...

You call a function fn by using parens () as in fn()

You access an item from a list by the indexing operator [] as in lst[idx]

So, by combining the two lst[idx](*args)

EDIT

Python list indices are zero-based, so for the first item is 0, the second 1, etc... If the user selects 1-4, you'll have to subtract one.

EDIT

Given the clarification, the following can be done

def method1():
    pass

def method2():
    pass


methods = [method1, method2]

And you can use the logic above. This way you won't have to mess with actual resolving the string of a name of the function to the actual function.

Keep in mind that functions in python are first class so you can store a reference of them to a list (what we do in methods=[] line)

edited May 31, 2015 at 21:45

answered May 31, 2015 at 21:11

Tasos Vogiatzoglou

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7 Comments

Tasos Vogiatzoglou Over a year ago

@RodrigoLópez I'm thinking in 0-based indexing :)

Rodrigo López Over a year ago

In question he selects from 1 to 4

luisfelipe18 Over a year ago

I just gave an example, exactly I'm using: method=['LU','CHOLESKY','Gauss', 'Gaussnopivot', 'Gaussconpivot', 'Gaussconviotparcial', 'Gaussconpivotcomp']

Tasos Vogiatzoglou Over a year ago

Where have you defined the methods ?

jonrsharpe Over a year ago

@LuisFelipeVillavicencioLopez they're strings, not methods. Are they the names of methods?

|

syntonym · Accepted Answer · 2015-05-31 21:52:42Z

2

In your list are not functions but strings (which have "randomly" the same name as the functions). Just put the functions inside the list:

def hello():
    pass

mylist = [hello]
mylist[0]()

If you need the name of a function you can use a.__name__ e.g.

def hello():
    pass
mylist = [hello]
print("Available functions:")
for function in mylist:
    print(function.__name__)

edited May 31, 2015 at 21:52

answered May 31, 2015 at 21:41

syntonym

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4 Comments

luisfelipe18 Over a year ago

But I need to use the name of the functions because I print a Menu where every method is enumerate, and I call the method by their enumeration.

syntonym Over a year ago

Use myfunc.__name__ to get the name of a function as a string.

luisfelipe18 Over a year ago

e.g print myfun.(hello) will print 'hello' ?

syntonym Over a year ago

If your function is called hello print(hello.__name__) will print "hello"

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