Passing different number of arguments into function

Question

I have a function:

def save(self, text, *index): 
    file.write(text + '\nResults:\n')
    if index == (): index = (range(len(self.drinkList)))
    for x in index:
        for y in self.drinkList[x].ing:
            file.write('min: ' + str(y.min) + ' max: ' + str(y.max) + ' value: ' + str(y.perc) + '\n')
        file.write('\n\n')
    file.write('\nPopulation fitness: ' + str(self.calculatePopulationFitness()) + '\n\n----------------------------------------------\n\n')

Now, when I pass one argument as an index the function works as it is supposed to, but when I pass a tuple of 2 indices I get an TypeError: list indices must be integers, not tuple. What should I change?

self.save('Resulted in ' , (index1, index2)) self.save('Resulted in ' , index) The first call gives an error, when I pass it without making it a tuple the resulting file is empty. — kyooryu
– kyooryu, Commented Nov 8, 2011 at 19:46

Riccardo Murri · Accepted Answer · 2011-11-08 19:48:58Z

5

The save(self, text, *index) syntax means that index is itself a tuple with all the arguments passed to save after the text one.

So, for instance, if you have in your code:

myobject.save("sample text", 1, 2, 3)

then index will be the tuple (1, 2, 3) and the for x in index will correctly loop over values 1, 2, 3.

On the other hand, if you haveL

myobject.save("sample text", (1,2))

then index will be the 1-element tuple ((1,2),) and the x in the loop will get the value (1,2), hence the TypeError.

answered Nov 8, 2011 at 19:48

Riccardo Murri

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HardlyKnowEm · Accepted Answer · 2011-11-08 19:54:39Z

3

It depends on what parameters you were actually trying to pass. I presume you called something to the effect of:

object.save("hello world", (3, 4, 5))

When you use the * operator, you do not need to pass the variable number of arguments as a tuple. Instead, everything that you pass after the fixed arguments is wrapped into a list. Therefore, in this case, the variable index refers to [(3, 4, 5)], not [3, 4, 5].

You should call the function save like this instead:

object.save("hello world", 3, 4, 5)

The variable index now refers to [3, 4, 5].

If, for some reason, you wanted to still pass a tuple, simply change your function definition to:

def save(self, text, index): # Observe the lack of '*'

answered Nov 8, 2011 at 19:54

HardlyKnowEm

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1 Comment

Michael Urman Over a year ago

Note that if you wish to continue to allow passing just one argument, this alternate could be something like def save(self, text, index=()).

hatmatrix · Accepted Answer · 2011-11-08 19:47:21Z

1

With the *index definition, you have to call the function as save(self, text, index1, index2), and index will be a tuple, (index1, index2). If you are passing a tuple to save after the argument, text, you can leave the * out.

answered Nov 8, 2011 at 19:47

hatmatrix

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Comments

MAK · Accepted Answer · 2011-11-08 19:47:13Z

0

Instead of calling your method with a tuple of indices like

x.save("ababs",(0,1))

Just call it with the indices one after another as if they were distinct paramaters to the method

x.save("ababs",0,1)

answered Nov 8, 2011 at 19:47

MAK

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