Call a Python function name from concantenated string name

Question

I want to create a def function name from concatenating "string" + variable + "string" and call that def function.

I am currently using this condensed version of code for simplicity to similarly accomplish tasks and I want to minimize the hard code contents of the function do_update(a):

ROTATE = '90'
ROT20 = [
[0, 0, 0, 0, 0, 0, 0, 0],
[126, 129, 153, 189, 129, 165, 129, 126],
[126, 255, 231, 195, 255, 219, 255, 126],
[0, 8, 28, 62, 127, 127, 127, 54],
[0, 8, 28, 62, 127, 62, 28, 8],
[62, 28, 62, 127, 127, 28, 62, 28],
[62, 28, 62, 127, 62, 28, 8, 8],
[0, 0, 24, 60, 60, 24, 0, 0],
];
def updatevalues90(a):
 b = []
 for i in range(8):
 for j in range(8):
 b[i] += a[j] + i
 return b
def do_update(a): 
 if ROTATE == '90':
 ROT = [updatevalues90(char) for char in a]
 elif ROTATE == '180': 
 ROT = [updatevalues180(char) for char in a]
 elif ROTATE == '270':
 ROT = [updatevalues270(char) for char in a]
do_update(ROT20)

Everything I have tried has resulted in Invalid Syntax or ROT filled with the string name of what I want.

I want to take the function call to updatevalues90(char) and instead of needing it hard coded, I want to change it to:

ROT = ["updatevalues" + ROTATE + "(char)" for char in a]

So that whatever value is in ROTATE will become part of the function call, i.e. function name.

My question is how in Python do I concatenate the strings and a variable name into a useable function name?

I think eval, but I can't get the syntax to work for me. Maybe there is something simpler in Python that works?

• Robert Harvey: Have you considered the possible security implications of this approach? There's a good chance you don't need this kind of flexibility at all. You might just need function overloading or an additional parameter to your function.
• ForceBru: "and a variable name" - it's not possible (or, possible, but unnecessarily difficult to do) to obtain the name of a variable used in an expression
• chepner: Ideally, you can define a single function that takes the angle of rotation as an additional parameter. I suspect the various updatevalues* functions look very similar.
• norok2: While probably not a good idea, what you actually are asking to do can be done with eval() and similar approaches.

Answer 1

Store your functions in a dict:

updaters = {
 '90': updatevalues90,
 '180': updatevalues180,
 '270': updatevalues270
}
def do_update(a):
 ROT = [updaters[ROTATE](char) for char in a]
 # return ROT ?

• WesZ: This looks sweet and what I'm looking for but I get this error and don't know why. ROT = [updaters['ROTATE'](char) for char in a] KeyError: 'ROTATE'
• chepner: Dumb mistake by me; I quoted the key instead of using the variable. I'll fix.
• WesZ: That was the first thing I checked and it errored on me after I fixed it....because I accidentally renamed a variable.... and didn't take a moment to go find it... So I went and found it. But hey, it's working like a champ! Thanks for that.... that's a sweet and simple approach and fix.