Python keywords and identifiers: parser rules differ from field rules

Operation contract

The fixture compiles an owned assignment using a reserved keyword and checks that it fails before execution. A soft keyword remains usable as a name outside its special grammar position. The receipt identifier validator imposes an ASCII application grammar instead of assuming every valid Python identifier is a valid received field. No received text is executed.

Failure and ownership boundary

Isidentifier does not check whether a name is reserved, and the set of soft keywords depends on the interpreter release. Unicode identifiers are valid in source but may be inappropriate for a protocol that needs a fixed alphabet. Compilation can raise SyntaxError before any statement runs. Python Unicode normalization: equality is not visual identity and Python type conversion: parsing success is not field validity concern different boundaries.

Working program

import keyword
import re

print("reserved:", keyword.iskeyword("class"))
print("valid spelling:", "class".isidentifier())
namespace = {}
exec(compile("match = 125", "owned-source", "exec"), namespace)
print("soft keyword value:", namespace["match"])
try:
    compile("class = 125", "owned-source", "exec")
except SyntaxError:
    print("reserved assignment rejected")
print("wire accepted:", re.fullmatch(r"[A-Z][A-Z0-9_]{0,15}", "RECEIPT_41") is not None)

Output

reserved: True
valid spelling: True
soft keyword value: 125
reserved assignment rejected
wire accepted: True

Costs and limits

Identifier scanning depends on source length. This fixture compiles fixed owned strings and validates a bounded field. Compiling received program text would introduce an execution boundary that this lesson does not provide.

Common Mistakes

• A valid identifier can still be reserved.
• Do not execute received text to validate a field.

Connected lessons

Python interpreter and virtual environments: run the intended executable, Python type conversion: parsing success is not field validity, Python Unicode normalization: equality is not visual identity.