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Errors handling

Errors handling

nuclear validates passed CLI arguments on running CliBuilder.run()

Handling syntax errors - CliSyntaxError

In case of syntax error, CliBuilder.run() raises CliSyntaxError, it's when:

  • parameter value is missing: --param-name without next argument
  • required parameter is not given
  • required positional argument is not given
  • positiona argument or parameter has invalid type (there was parsing type error)

By default CliSyntaxError caught by CliBuilder is rethrown. You can disable raising this error again by seting reraise_error = False when creating CliBuilder: CliBuilder(reraise_error = False). Then only the error log will be displayed in console stdout.

usage_onerror parameter decides wheter usage output should be displayed on syntax error.

Erros handling example

#!/usr/bin/env python3
from nuclear import CliBuilder, argument

CliBuilder(usage_onerror=False).has(
    argument('remote', required=True),
).run()

foo@bar:~$ ./pos-args.py
[ERROR] Syntax error: required positional argument "remote" is not given

CliDefinitionError

In case of invalid CLI definition, CliBuilder.run() raises CliDefinitionError. It's e.g. when:

  • positional argument or parameter is set to required and has default value set (it doesn't make any sense)
  • positional argument is placed after all remaining arguments
  • parameter / argument value does not belong to strict available choices list

Wrong CLI Definition example

#!/usr/bin/env python3
from nuclear import CliBuilder, argument

CliBuilder().has(
    argument('remote', required=True, default='def'),
).run()

foo@bar:~$ ./errors.py
[ERROR] CLI Definition error: argument value may be either required or have the default value
Traceback (most recent call last):
  File "pyt.py", line 4, in <module>
    argument('remote', required=True, default='def'),
  File "~/nuclear/nuclear/builder/builder.py", line 69, in run
    self.run_with_args(sys.argv[1:])
  File "~/nuclear/nuclear/builder/builder.py", line 76, in run_with_args
    raise e
  File "~/nuclear/nuclear/builder/builder.py", line 73, in run_with_args
    Parser(self.__subrules).parse_args(args)
  File "~/nuclear/nuclear/parser/parser.py", line 37, in __init__
    self._init_rules()
  File "~/nuclear/nuclear/parser/parser.py", line 57, in _init_rules
    raise CliDefinitionError('argument value may be either required or have the default value')
nuclear.parser.error.CliDefinitionError: argument value may be either required or have the default value