Creating a list of methods to be executed in Python

Question

How can I create a list of methods in python to be applied to an object?

Given some arbitrary class:

class someClass:
    def __init__(self, s):
        self.size = s

    def shrink(self):
        self.size -= 1

    def grow(self):
        self.size += 1

    def invert(self):
        self.size = -self.size

I want to be able to write an iterable object like this list:

instructions = [shrink, grow, shrink, shrink, grow, invert]

To be run through a for-loop later:

elephant = someClass(90)
sizeList = []
for ins in instructions:
    elephant.ins()
    sizeList.append(elephant.size)

I've done something similar with functions before. Not being able to do this with methods would require me to rewrite an intimidating amount of code...

you can also use someClass.__dict__[ins](elephant), otherwise getattr() is good. — Ashwini Chaudhary
– Ashwini Chaudhary, Commented Oct 2, 2012 at 21:46
@Ashwini Looking at the docs, .__dict__ is an implementation detail. Why would you ever use it instead of getattr() anyway? — wjandrea
– wjandrea, Commented Nov 2, 2022 at 22:44

wjandrea · Accepted Answer · 2022-11-02 22:46:14Z

6

You could create a list of the method names then use getattr() to access the methods:

instructions = ["shrink", "grow", "shrink"]
for i in instructions:
     getattr(elephant, i)()

edited Nov 2, 2022 at 22:46

wjandrea

33.9k10 gold badges69 silver badges105 bronze badges

answered Oct 2, 2012 at 21:33

Joran Beasley

114k13 gold badges167 silver badges187 bronze badges

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

Comments

Andrew Clark · Accepted Answer · 2012-10-02 21:36:57Z

3

As an alternative to using strings for your list of instructions, you could do the following:

instructions = [someClass.shrink, someClass.grow, someClass.shrink,
                someClass.shrink, someClass.grow, someClass.invert]
elephant = someClass(90)
sizeList = []
for ins in instructions:
    ins(elephant)
    sizeList.append(elephant.size)

answered Oct 2, 2012 at 21:36

Andrew Clark

210k36 gold badges285 silver badges310 bronze badges

1 Comment

user-asterix Over a year ago

+1, for showing that you can call a method as if it is a function by passing the instance as a parameter; in this case elephant instance will be passed as the self parameter to the method (function)

kojiro · Accepted Answer · 2012-10-02 21:33:35Z

0

Possibly naïvely:

for ins in instructions:
  getattr(elephant, ins)()

Gotchas include that ins must be a string and that it's probably wise to validate both that ins is what you really want to call and that getattr(elephant, ins) is a callable.

answered Oct 2, 2012 at 21:33

kojiro

77.8k20 gold badges151 silver badges217 bronze badges

Comments

phihag · Accepted Answer · 2012-10-03 15:28:38Z

0

You can use dir to get all property names of an object, and getattr to get a property value of an object. You may also want to not call any non-callable properties (such as 2 or "foo"):

for m in dir(elephant):
    if not m.startswith('_'):
        f = getattr(elephant, m)
        if callable(f): # Do not try to call non-function properties
            f()

edited Oct 3, 2012 at 15:28

answered Oct 2, 2012 at 21:34

phihag

289k75 gold badges475 silver badges489 bronze badges

1 Comment

phant0m Over a year ago

You might want to integrate callable()

Collectives™ on Stack Overflow

Creating a list of methods to be executed in Python

4 Answers 4

Comments

1 Comment

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

1 Comment

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related