all Python 3deprecated in 3.9astterm

ast.Param

variables

Deprecated since 3.9: an expression context left over from Python 2, where it marked function parameters; the Python 3 parser never produces it.

Syntax

ast.Param()

In Python 3 parameters are separate arg nodes with no ctx field, so Param never appears in a tree from ast.parse, and compile() rejects one inserted by hand. The class still imports, and code testing isinstance(ctx, ast.Param) silently finds nothing; look for ast.arg instead. It is slated for removal in a future version together with Suite, AugLoad and AugStore.

Examples

import ast
tree = ast.parse('def f(a, b): pass')
params = [n.arg for n in ast.walk(tree) if isinstance(n, ast.arg)]
print(params)  # → ['a', 'b']
print(any(isinstance(getattr(n, 'ctx', None), ast.Param) for n in ast.walk(tree)))  # → False

import ast
m = ast.parse('x = 1')
m.body[0].targets[0].ctx = ast.Param()
try:
    compile(m, '<ast>', 'exec')
except TypeError as e:
    print(type(e).__name__)  # → TypeError

See also

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