The default argument is mutable

Reports a problem when a mutable value as a list or dictionary is detected in a default value for an argument.

Default argument values are evaluated only once at function definition time, which means that modifying the default value of the argument will affect all subsequent calls of that function.

Example:

def func(s, cache={}):
    cache[s] = None

When the quick-fix is applied, the code changes to:

def func(s, cache=None):
    if cache is None:
        cache = {}
    cache[s] = None

Locating this inspection

By ID

Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

PyDefaultArgument

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | Python

Inspection ID: PyDefaultArgumentInspection

Suppressing Inspection

You can suppress this inspection by placing the following comment marker before the code fragment where you no longer want messages from this inspection to appear:

//noinspection PyDefaultArgument

More detailed instructions as well as other ways and options that you have can be found in the product documentation:

Inspection Details
By default bundled with:	CLion 2025.2, DataSpell 2025.2, IntelliJ IDEA 2025.2, PyCharm 2025.2, Qodana for JVM 2025.2,

Last modified: 18 September 2025