Python Function Arguments With Default Arguments

I am new to python. I want to define a function with from and to date. If I call the function with one argument, It should take that argument as to date. If I pass two arguments, I

Solution 1:

Required arguments must come before default arguments, otherwise python doesn't know which one the value is meant for.

See Dive into python section on default and named arguments.

Solution 2:

When you are passing a value default argument, all arguments to the right of it should also have default values.

This holds true for C++ as well.

Eg:

Validdef example(a = 1, b = 2):passValiddef example(a , b = 2):pass

Errordef example(a = 1, b):pass

Solution 3:

As error message says, default arguments should follow non-default ones, like this:

def__init__(self, edate, fdate=""):
    self.fdate = fdate
    self.edate = edate

Refer to docs where this behaviour is clearly depicted.

Solution 4:

SyntaxError: non-default argument follows default argument

Your default arguments must come later to non default arguments.

The reason: Your interpreter will have a hard time assigning the arguments if you do a mix up. So it doesn't support it and throws a SyntaxError.

Just change it to

def__init__(self, edate, fdate=""):

@Edit1: Few languages like Kotlin allows you to have default args before non-default args. In this case you will be using a named arg to set the function parameters.

Solution 5:

Here is how I would solve it: I would write a small class and two factory functions that call the class constructor and return the result:

classDateRange:def__init__(self, dfrom='', dto=''):
        self.dfrom = dfrom
        self.dto = dto

defdate_from_to(dfrom, dto):
    return DateRange(dfrom, dto)

defdate_to(dto):
    return DateRange(dto=dto)

As you have seen from the error message, you can't define a function that behaves the way you want. If you use two functions it's easy enough to document them and to remember how to use them.