How to apply self in method parameter in Python

Question

Actually , I want to write

def w_cell(self, r, c, val, style=XLS.get_cell_stlye(self))

But it cannot, and show me the error

NameError: name 'self' is not defined

How could I set the default style in parameter rather than in function.

Thanks

class XLS():

    def get_cell_stlye(self):        
        return xlwt.easyxf("alignment: horizontal center,\
         vertical center, wrap true ;")


class TestCGI(object, XLS):
    def w_cell(self, r, c, val, style='null'):
            if style == 'null':
                style=XLS.get_cell_stlye(self)
            self.sht.write(r, c, val, style)

score 0 · Answer 1 · answered Sep 27 '13 at 03:54

The short answer is that you can't write that. Default arguments are evaluated when the function is created. At the function creation time, self doesn't exist yet¹, so it can't have anything to do with the calculation of the default value.

^{¹after all, if the class doesn't exist yet, it can't have any instances -- and even if it did, which instance would it pick to be self?}

cjfro · Accepted Answer · 2013-09-27T04:24:10.320

0

Setting it in the function itself is fine, although you probably want to do it like this:

class TestCGI(object, XLS):
    def w_cell(self, r, c, val, style=None):
        if style is not None:
            style=XLS.get_cell_stlye(self)
        self.sht.write(r, c, val, style)

edited Sep 27 '13 at 04:24

answered Sep 27 '13 at 03:57

cjfro

224
1
7

In this case, I would is `if style is not None` -- Your version would also pick up `style=0` which may or may not be meaningful. – mgilson Sep 27 '13 at 03:58

How to apply self in method parameter in Python

2 Answers2