Validate command-line inputs
Convert argparse strings deliberately and handle invalid command-line values.
Convert at the input boundary
argparse can produce strings; coerce=True lets the validation step explicitly convert supported values. The example supplies an argument list so it runs reproducibly; use parser.parse_args() for real command-line arguments.
import argparse
from zodify import validate
parser = argparse.ArgumentParser()
parser.add_argument("--port", required=True)
parser.add_argument("--debug", default="false")
schema = {"port": int, "debug": bool}
args = vars(parser.parse_args(["--port", "8080", "--debug", "yes"]))
print(validate(schema, args, coerce=True))
try:
validate(schema, {"port": "not-a-port", "debug": "false"}, coerce=True)
except ValueError as error:
print(f"ValueError: {error}")
Output
{'port': 8080, 'debug': True}
ValueError: port: cannot coerce 'not-a-port' to intConversion limits
Add a predicate if a port must fall within a specific range. Boolean conversion recognizes a small vocabulary. Handle errors with an application-controlled message if arguments may contain secrets.
For a single argument, argparse's built-in type or choices may be enough. Use a shared validation schema when the same shape also comes from another boundary.