Is there a more Pythonic way to access to functions via their string name?

Question

I have a few functions (hardcoded, I don't want Python to compute the derivatives, in reality the functions are more complex):

def f(x): return x
def g(x): return x ** 2
def f_prime(x): return 1
def g_prime(x): return 2 * x

and a list a functions:

myfunctions = [f, f, g, f]

How to get the list of the related "prime" functions?

I was thinking about:

myderivatives = [globals()[function.__name__ + '_prime'] for function in myfunctions]

and it works:

[<function f_prime at 0x00000000022CF048>, <function f_prime at 0x00000000022CF048>, <function g_prime at 0x00000000022CF0B8>, <function f_prime at 0x00000000022CF048>]

but is there a more Pythonic way to get the list of the "prime" functions associated to the original versions?

Also there is a corner case:

from module1 import thisfunction as f
def f_prime(x): 
    pass

globals()[f.__name__ + '_prime']  
# doesn't work because f.__name__ + '_prime' is 'thisfunction_prime' and not 'f_prime'

You could have the derivatives as attributes of the original functions. — Matthieu Brucher
– Matthieu Brucher, Commented Nov 13, 2018 at 11:44

jpp · Accepted Answer · 2018-11-13 11:47:23Z

5

Define a dictionary to hold your functions and then use a list comprehension:

funcd = {'f': f, 'g': g, 'f_prime': f_prime, 'g_prime': g_prime}

myderivatives = [func for name, func in funcd.items() if name.endswith('_prime')]

The benefit of this solution is it defines precisely the scope of functions you wish to filter. Use of globals is not recommended, and very rarely necessary.

answered Nov 13, 2018 at 11:47

jpp

166k37 gold badges301 silver badges363 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

aydow · Accepted Answer · 2018-11-13 11:54:18Z

3

Following on from jpp's answer you could arrange the functions in a dict mapping from function to derivative like so

In [64]: primes = {f: f_prime, g: g_prime}

In [65]: primes.values()
Out[65]: dict_values([<function g_prime at 0x7f3594174c80>, <function f_prime at 0x7f3594174a60>])

In [66]: primes[f]
Out[66]: <function __main__.f_prime(x)>

answered Nov 13, 2018 at 11:54

aydow

3,8313 gold badges28 silver badges41 bronze badges

Collectives™ on Stack Overflow

Is there a more Pythonic way to access to functions via their string name?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related