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For instance, I want:
def func(n=5.0,delta=n/10):
If the user has specified a delta, use it. If not, use a value that depends on n. Is this possible?
222
In addition to passing arguments to functions via a function call, you can also set default argument values in Python functions.
Function arguments can have default values in Python. We can provide a default value to an argument by using the assignment operator (=).
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. Let's understand this through a function student.
A default argument is a value provided in a function declaration that is automatically assigned by the compiler if the calling function doesn't provide a value for the argument. In case any value is passed, the default value is overridden.
The language doesn't support such syntax.
The usual workaround for these situations(*) is to use a default value which is not a valid input.
def func(n=5.0, delta=None):
if delta is None:
delta = n/10
(*) Similar problems arise when the default value is mutable.
65
You can't do it in the function definition line itself, you need to do it in the body of the function:
def func(n=5.0,delta=None):
if delta is None:
delta = n/10
You could do:
def func(n=5.0, delta=None):
if delta is None:
delta = n / 10
...
These answers will work in some cases, but if your dependent argument (delta) is a list or any iterable data type, the line
if delta is None:
will throw the error
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
If your dependent argument is a dataframe, list, Series, etc, the following lines of code will work better. See this post for the idea / more details.
def f(n, delta = None):
if delta is f.__defaults__[0]:
delta = n/10
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