positional(max_positional_args)
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A decorator to declare that only the first N arguments my be positional.
This decorator makes it easy to support Python 3 style key-word only
parameters. For example, in Python 3 it is possible to write:
def fn(pos1, *, kwonly1=None, kwonly1=None):
...
All named parameters after * must be a keyword:
fn(10, 'kw1', 'kw2') # Raises exception.
fn(10, kwonly1='kw1') # Ok.
Example:
To define a function like above, do:
@positional(1)
def fn(pos1, kwonly1=None, kwonly2=None):
...
If no default value is provided to a keyword argument, it becomes a required
keyword argument:
@positional(0)
def fn(required_kw):
...
This must be called with the keyword parameter:
fn() # Raises exception.
fn(10) # Raises exception.
fn(required_kw=10) # Ok.
When defining instance or class methods always remember to account for
'self' and 'cls':
class MyClass(object):
@positional(2)
def my_method(self, pos1, kwonly1=None):
...
@classmethod
@positional(2)
def my_method(cls, pos1, kwonly1=None):
...
The positional decorator behavior is controlled by the
--positional_parameters_enforcement flag. The flag may be set to 'EXCEPTION',
'WARNING' or 'IGNORE' to raise an exception, log a warning, or do nothing,
respectively, if a declaration is violated.
Args:
max_positional_arguments: Maximum number of positional arguments. All
parameters after the this index must be keyword only.
Returns:
A decorator that prevents using arguments after max_positional_args from
being used as positional parameters.
Raises:
TypeError if a key-word only argument is provided as a positional parameter,
but only if the --positional_parameters_enforcement flag is set to
'EXCEPTION'.
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