Python 3.3+inspectterm

inspect.Parameter

signatures

A single parameter of a signature: its name, kind (positional, keyword, *args, **kwargs), default value and annotation.

Syntax

inspect.Parameter(name, kind, *, default=Parameter.empty, annotation=Parameter.empty)

'No default' is Parameter.empty, not None: default=None is a real default, so checking 'p.default is None' mixes up the two cases. Read the kind from p.kind (POSITIONAL_ONLY … VAR_KEYWORD) instead of guessing from the stars in str(p); kinds are ordered and compare with <. The object is immutable: assigning p.default raises AttributeError, and p.replace(default=...) gives a modified copy.

Examples

import inspect
def f(a, /, b, *args, c, d=None, **kw): pass
for p in inspect.signature(f).parameters.values():
    print(p.name, p.kind.name)
# → a POSITIONAL_ONLY / b POSITIONAL_OR_KEYWORD / args VAR_POSITIONAL / c KEYWORD_ONLY / d KEYWORD_ONLY / kw VAR_KEYWORD

# Python 3.11+
import inspect
params = inspect.signature(lambda c, d=None: 0).parameters
print(params['c'].default is inspect.Parameter.empty)  # → True
print(params['d'].default is inspect.Parameter.empty, params['d'].default)  # → False None
print(params['d'].replace(default=5))  # → d=5
try:
    params['d'].default = 5
except AttributeError as e:
    print(e)  # → property 'default' of 'Parameter' object has no setter

See also

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