Use a string to call function in Python

Question

Some days ago I was searching on the net and I found an interesting article about python dictionaries. It was about using the keys in the dictionary to call a function. In that article the author has defined some functions, and then a dictionary with key exactly same as the function name. Then he could get an input parameter from user and call the same method (something like implementing case break)
After that I realised about the same thing but somehow different. I want to know how I can implement this.
If I have a function:

def fullName( name = "noName", family = "noFamily" ):
    return name += family

And now if I have a string like this:

myString = "fullName( name = 'Joe', family = 'Brand' )"

Is there a way to execute this query and get a result: JoeBrand
For example something I remember is that we might give a string to exec() statement and it does it for us. But I’m not sure about this special case, and also I do not know the efficient way in Python. And also I will be so grateful to help me how to handle that functions return value, for example in my case how can I print the full name returned by that function?

Asked By: user435245

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Answer 1

You could use eval():

myString = "fullName( name = 'Joe', family = 'Brand' )"
result = eval(myString)

Beware though, eval() is considered evil by many people.

Answered By: Frédéric Hamidi

Answer 2

This does not exactly answer your question, but maybe it helps nevertheless:

As mentioned, eval should be avoided if possible. A better way imo is to use dictionary unpacking. This is also very dynamic and less error prone.

Example:

def fullName(name = "noName", family = "noFamily"):
    return name + family

functionList = {'fullName': fullName}

function = 'fullName'
parameters = {'name': 'Foo', 'family': 'Bar'}

print functionList[function](**parameters)
# prints FooBar

parameters = {'name': 'Foo'}
print functionList[function](**parameters)
# prints FoonoFamily

Answered By: Felix Kling

Answer 3

I know this question is rather old, but you could do something like this:

argsdict = {'name': 'Joe', 'family': 'Brand'}
globals()['fullName'](**argsdict)

argsdict is a dictionary of argument, globals calls the function using a string, and ** expands the dictionary to a parameter list. Much cleaner than eval. The only trouble lies in splitting up the string. A (very messy) solution:

example = 'fullName(name='Joe',family='Brand')'
# Split at left parenthesis
funcname, argsstr = example.split('(')
# Split the parameters
argsindex = argsstr.split(',')
# Create an empty dictionary
argsdict = dict()
# Remove the closing parenthesis
# Could probably be done better with re...
argsindex[-1] = argsindex[-1].replace(')', '')
for item in argsindex:
    # Separate the parameter name and value
    argname, argvalue = item.split('=')
    # Add it to the dictionary
    argsdict.update({argname: argvalue})
# Call our function
globals()[funcname](**argsdict)

Answered By: kirbyfan64sos

Use a string to call function in Python

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