Python define function default value

Function definitions

As you can see, the list keeps getting longer and longer. The reason is simple: The workaround is, as others have mentioned, to use a placeholder value instead of modifying the default value.

None is a common value:. Finally, it should be noted that more advanced Python code often uses this mechanism to its advantage; for example, if you create a bunch of UI buttons in a loop, you might try something like:.

To fix this, use explicit binding:. It happened to me in one of the first Python programs I ever wrote, and it took several years before we spotted the non-critical bug, when someone looked a bit more carefully at the contents of a property file, and wondered what all those things were doing there….

When it does this, it also evaluates the default values. The various components are available as attributes on the function object; using the function we used above:.

Python will then create a new binding to the code object, evaluate the defaults, and assign the function object to the same variable as before. And yes, if you happen to have the pieces but not the function, you can use the function class in the new module to create your own function object.

4. More Control Flow Tools — Python documentation

Fredrik Lundh July 17, based on a comp. Why does this happen?

Common Gotchas — The Hitchhiker's Guide to Python

What to do instead? None is a common value: To fix this, use explicit binding: How does this work, in detail? The various components are available as attributes on the function object; using the function we used above: Valid uses for mutable defaults How does this work, in detail?