Python, how can I initialize a variable during function/method calls

Question

In most interpreted languages (example given in psuedo PHP) I would be able to do something like this

function f($name, &$errors = null) {
    if(something_wrong) {
        if(!is_null($errors) {
            $errors[] = 'some error';
        }
        return false;
    }
}

if(!f('test', $errs = array()) {
    print_r($errs);
}

And get a result like

Array
(
     [0] => some error
)

However when I try this in Python

def f(name, errors = None):
    if something_wrong:
        if errors:
            errors.append('some error')
        return False


if not f('test', errs = []):
    print str(errs)

I get an error

TypeError: f() got an unexpected keyword argument 'errs'

Which makes perfect sense in the context of Python thinking I am trying to set a specific argument, and not create a new variable altogether.

However if I try

if not f('test', (errs = [])):
    print str(errs)

I get

    f('test', (errs = []))
                    ^
 SyntaxError: invalid syntax

Because I think now it assumes I am trying to create a tuple.

Is there any way to keep this code on one line, or do I absolutely have to initialise the variable on it's own before passing it to the function/method? From what I can tell the only solution is this

errs = []
if not f('test', errs):
    print str(errs)

Xiaoqi Chu · Accepted Answer · 2015-11-09 19:37:01Z

1

It should be called as f(name, errors = []) or f(name, []). If you want to init with attribute name, python requires the variable key you given is same with any attribute name you declared in the function definition.

answered Nov 9, 2015 at 19:37

Xiaoqi Chu

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1 Comment

Chris Nasr Over a year ago

I don't see how this helps me, in fact you've completely removed the initialization of errs, so there's no way I can access it after the function call is completed.

pBuch · Accepted Answer · 2015-11-09 19:55:41Z

0

"In Python, assignment is a statement, not an expression, and can therefore not be used inside an arbitrary expression."

see http://effbot.org/pyfaq/why-can-t-i-use-an-assignment-in-an-expression.htm

answered Nov 9, 2015 at 19:55

pBuch

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1 Comment

Chris Nasr Over a year ago

Thank you pBuch, that's what I was looking for. :)

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