Python - change string into arguments and pass it to a function

Question

I am using python with a mysql db. I have a table in that db storing names of functions to be run.
I would like to also add a possibility to store variables in the table, retrieve them on the fly and pass them into the function. However when stored in the db, the arguments are strings, and I don't know how to convert them to variable names to pass to the function.

For instance lets consider the following example where the table contains:

module        function      arguments  (<--columns names)
indicators    scrape_web    datapoints

Let's say that I retrieve the data with a mysql lib and save it in a dict such as:

script:{'module': 'indicators',
        'function': 'scrape_web',
        'arguments': 'datapoints'}

I can retrieve the module and function name, and run the function without arguments like that :

module = __import__(script['module'])
func = getattr(module, script['function'])
func()

But what if i want to pass the arguments into the function so that the function run func(datapoints)

func(script['arguments'])

Obviously doesn't work.

All help greatly appreciated.

Are you trying to call func('datapoints') or func(datapoints) (where datapoints is a variable containing some data)? — gen_Eric
– gen_Eric, Commented Mar 28, 2017 at 16:45
@Rocket Hazmat as mentionned in the question , func(datapoints) — jim jarnac
– jim jarnac, Commented Mar 28, 2017 at 16:46
@user2357112 in the namespace of the script running the function func — jim jarnac
– jim jarnac, Commented Mar 28, 2017 at 16:47
If the args are in the calling code's global namespace then you can access them by name with, eg globals()['datapoints'] — PM 2Ring
– PM 2Ring, Commented Mar 28, 2017 at 16:58

Kochoba · Accepted Answer · 2017-03-28 18:23:24Z

3

Assuming script['arguments'] returns a string which is the name of a variable.

func(eval(script['arguments']))

For multiple arguments split the string using script['arguments'].split(",") and use eval for each element in the list.

If you want this to be as generic as possible:

args = script(['arguments']).split(",")
fstr = 'func('
for i in range(0,len(args)) : fstr +='eval(args['+str(i)+']),'
fstr = fstr[:-1]
#to remove the trailing comma
fstr += ')'
eval(fstr)

edited Mar 28, 2017 at 18:23

answered Mar 28, 2017 at 16:55

Kochoba

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7 Comments

jim jarnac Over a year ago

that is great thx - what if the function takes multiple arguments? For instance if script:{'module': 'indicators', 'function': 'scrape_web', 'arguments': 'datapoints, 25'} ?

Kochoba Over a year ago

Use script['arguments'].split(",") to get a list of the arguments and call eval for each argument

Kochoba Over a year ago

@jimbasquiat I updated my answer to incorporate your comment

jim jarnac Over a year ago

I have been trying func([eval(x) for x in script['arguments'].split(",")]) but i receive the error message: missing 1 required positional argument. Any what is the expression i should actually use?

Kochoba Over a year ago

@jimbasquiat [eval(x) for x in script['arguments'].split(",")] will return a list so it will be 1 argument. Either your function should take a list or you should pass the arguments at the respective positions. args= script['arguments'].splti(",") func(eval(args[0]) , eval(args[1]) .. etc)

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