Optional parameters: Difference between revisions

Content added Content deleted
Line 522: Line 522:
See the Python entry in [[Named_Arguments#Python|Named Arguments]] for a more comprehensive description of Python function parameters and call arguments.
See the Python entry in [[Named_Arguments#Python|Named Arguments]] for a more comprehensive description of Python function parameters and call arguments.


Note that expression for a default argument of an optional parameter is evaluated only once when the function is defined, and all calls of the function where that parameter is missing will be initialized to point to that same shared object. So, if the default argument value is a mutable object (e.g. list, dict, etc.), then any changes to it will affect what is seen by future calls of the function:
Note that expression for a default argument of an optional parameter is evaluated only once, when the function definition is executed, and all calls of the function where that parameter is missing will be initialized to point to that same shared object. So, if the default argument value is a mutable object (e.g. list, dict, etc.), then any changes to it will affect what is seen by future calls of the function:
<pre>
<pre>
>>> def foo(x, lst=[]):
>>> def foo(x, lst=[]):
Retrieved from "https://rosettacode.org/wiki/Optional_parameters"