Elegant way to set class variables without elseif

Question

I am new to python, so I am sorry if there is an obvious solution. I am working on someones code which looks like this (with a total of 80 entries):

class variable():
number = ""

def __init__(self, number):
    self.no = number
    self.longname = "Long variable name"
    self.name = "Variable"
    self.tag = "tag"
    self.unit = "unit"

def get_varname(self):

    if self.no == 1:
        self.name = 'Second'
        self.unit = '[s]'
    elif self.no == 2:
        self.name = 'Metre'
        self.unit = '[m]'
    elif self.no == 3:
        self.name = 'Kilogram'
        self.tag = 'kg'
        self.unit = '[kg]'
    elif self.no == 4:
        self.name = 'Ampere'
        self.tag = 'Amp'
        self.unit = '[A]'

Is there any elegant way to rewrite this? I guess one way to do it is with a dictionary, but I am not sure if this makes the code easier. Also only some entries contain "tag".

ah this makes sense. But how do I deal with self.tag not occuring in every place? Would this mean that I have to simply insert "tag" into every dictionary entry? — ATYslh
– ATYslh, Commented Apr 26, 2021 at 15:24
@ATYslh See my answer for more information on how to do that — KarmaPenny
– KarmaPenny, Commented Apr 26, 2021 at 15:26

KarmaPenny · Accepted Answer · 2021-04-26 15:24:31Z

Using A Dictionary

Like @deceze said, using a dict mapping the number to a tuple is one way. What you could do is set up the tuple like so: ("Name", "unit", "tag - optional"). Then, you could take the size of the tuple to see if it has a tag or not. So, the dict would look like:

class variable():
    def __init__(self, number):
        self.no = number
        self.longname = "Long variable name"
        self.name = "Variable"
        self.tag = "tag"
        self.unit = "unit"
        self.map = {1: ('Second','[s]'), 2: ('Metre', '[m]'), 
                         3: ('Kilogram', '[kg]', 'kg'), 4: ('Ampere', '[A]', 'Amp')}
    def get_varname(self):
        selfTuple = self.map[self.no]
        self.name = selfTuple[0]
        self.unit = selfTuple[1]
        if (len(selfTuple)==3):
            self.tag = selfTuple[2]

Using Match Case in 3.10

In Python 3.10, you can use a special statement called match case. It is similar to the switch statement in Java.

class variable():
    def __init__(self, number):
        self.no = number
        self.longname = "Long variable name"
        self.name = "Variable"
        self.tag = "tag"
        self.unit = "unit"
    def get_varname(self):
        match self.no:
            case 1:
                self.name = 'Second'
                self.unit = '[s]'
            case 2:
                self.name = 'Metre'
                self.unit = '[m]'
            case 3:
                self.name = 'Kilogram'
                self.tag = 'kg'
                self.unit = '[kg]'
            case 4:
                self.name = 'Ampere'
                self.tag = 'Amp'
                self.unit = '[A]'

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