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Consider the following function, which does not work in Python, but I will use to explain what I need to do.
def exampleFunction(a, b, c = a): ...function body... That is I want to assign to variable c the same value that variable a would take, unless an alternative value is specified. The above code does not work in python. Is there a way to do this?
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Python has a different way of representing syntax and default values for function arguments. Default values indicate that the function argument will take that value if no argument value is passed during the function call. The default value is assigned by using the assignment(=) operator of the form keywordname=value.
Introduction to Python default parameters When you define a function, you can specify a default value for each parameter. In this syntax, you specify default values ( value2 , value3 , …) for each parameter using the assignment operator ( =) .
Default arguments in Python functions are those arguments that take default values if no explicit values are passed to these arguments from the function call.
Python input() Function By default, it returns the user input in form of a string.
def example(a, b, c=None): if c is None: c = a ... The default value for the keyword argument can't be a variable (if it is, it's converted to a fixed value when the function is defined.) Commonly used to pass arguments to a main function:
def main(argv=None): if argv is None: argv = sys.argv If None could be a valid value, the solution is to either use *args/**kwargs magic as in carl's answer, or use a sentinel object. Libraries that do this include attrs and Marshmallow, and in my opinion it's much cleaner and likely faster.
missing = object() def example(a, b, c=missing): if c is missing: c = a ... The only way for c is missing to be true is for c to be exactly that dummy object you created there.
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This general pattern is probably the best and most readable:
def exampleFunction(a, b, c = None): if c is None: c = a ... You have to be careful that None is not a valid state for c.
If you want to support 'None' values, you can do something like this:
def example(a, b, *args, **kwargs): if 'c' in kwargs: c = kwargs['c'] elif len(args) > 0: c = args[0] else: c = a If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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