Dictionary of Functions

[bumsfeld]

I was trying to come up with a dictionary of functions, but get it not to work.

[vegaseat]

Sorry, mindreading is not my métier. Please gives us an example of your code and the error message you get.

[G-Do]

You mean something like this?

import re
f = dict()
f["compile"] = re.compile
f["findall"] = re.findall
f["match"] = re.match
pattern = f["compile"]("[\\w]+")

This works for me.

[bumsfeld]

Thanks G-Do! I think you gave me a good hint where i went wrong. Here is my error prone code:

# a dictionary of functions by bumsfeld
# get errors = TypeError: 'int' object is not callable

def add(a, b):
    return a + b

def sub(a, b):
    return a - b

def mul(a, b):
    return a * b

def div(a, b):
    return a / b

a = b = 1

mathD = {
'+' : add(a, b),
'-' : sub(a, b),
'*' : mul(a, b),
'/' : div(a, b)
}

f = mathD['+']
print f(99, 13)

[vegaseat]

G-Do did give you the hint, don't call the functions from the dictionary, just reference them. I took the liberty to play with your code a little ...

def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

def multiply(a, b):
    return a * b

def divide(a, b):
    if b == 0:
        print "divide by zero error"
    else:
        return a / b

# use the function reference, not the actual call
mathD = {
'+' : add,
'-' : subtract,
'*' : multiply,
'/' : divide
}


f = mathD['+']
print f(99, 13)

# or simpler ...
print mathD['+'](99, 13)

# maybe less cryptic ...
def calc(math_op, a, b):
    return mathD[math_op](a, b)

# now you can use ...
print calc('/', 355, 113.0)

[bumsfeld]

How can you handle the wrong symbol? Like someone uses '**' and not '*'

[vegaseat]

That's where the calc() function would come in handy, change it to ...

def calc(math_op, a, b):
    if math_op in mathD:
        return mathD[math_op](a, b)
    else:
        print "'%s' not recognized" % math_op

[Kyss]

That is not necessarily the OP's actual question,
(does not even have a dictionary of functions)
but I was facing the problem that I needed something like the calc function
that vegaseat suggested and this is what I came up with:

mathD = {
    '+': '__add__',
    '-': '__sub__',
    '*': '__mul__',
    '/': '__div__'
}

def calc(op, a, b):
    method = getattr(a,mathD[op])
    return method(b)

Saves me writing down all the defs :D

[TrustyTony]

You are better off using the ready definitions from the operator module.
http://www.daniweb.com/software-development/python/threads/453521/code-efficiency-and-a-general-checkup#post1968019

[Kyss]

Thanks for the tip. Now it look even better. (And I am using a dictionary of functions.)

from operator import add, sub, mul, div

mathD = {
    '+': add,
    '-': sub,
    '*': mul,
    '/': div
}

def calc(op, a, b):
    return mathD[op](a,b)