ubelt.util_func module

Helpers for functional programming.

The identity() function simply returns its own inputs. This is useful for bypassing print statements and many other cases. I also think it looks a little nicer than lambda x: x.

The inject_method() function “injects” another function into a class instance as a method. This is useful for monkey patching.

ubelt.util_func.identity(arg=None, *args, **kwargs)[source]

The identity function. Simply returns the value of its first input.

All other inputs are ignored. Defaults to None if called without args.

Parameters

  • arg (object, default=None) – some value

  • *args – ignored

  • **kwargs – ignored

Returns

arg - the same value

Return type

object

Example

>>> import ubelt as ub
>>> ub.identity(42)
42
>>> ub.identity(42, 42)
42
>>> ub.identity()
None
ubelt.util_func.inject_method(self, func, name=None)[source]

Injects a function into an object instance as a bound method

The main use case of this function is for monkey patching. While monkey patching is sometimes necessary it should generally be avoided. Thus, we simply remind the developer that there might be a better way.

Parameters

  • self (T) – instance to inject a function into

  • func (Callable[[T, …], Any]) – the function to inject (must contain an arg for self)

  • name (str, default=None) – name of the method. optional. If not specified the name of the function is used.

Example

>>> import ubelt as ub
>>> class Foo(object):
>>>     def bar(self):
>>>         return 'bar'
>>> def baz(self):
>>>     return 'baz'
>>> self = Foo()
>>> assert self.bar() == 'bar'
>>> assert not hasattr(self, 'baz')
>>> ub.inject_method(self, baz)
>>> assert not hasattr(Foo, 'baz'), 'should only change one instance'
>>> assert self.baz() == 'baz'
>>> ub.inject_method(self, baz, 'bar')
>>> assert self.bar() == 'baz'
ubelt.util_func.compatible(config, func, start=0)[source]

Take the subset of dict items that can be passed to function as kwargs

Parameters

  • config (dict) – a flat configuration dictionary

  • func (Callable) – a function or method

  • start (int, default=0) – Only take args after this position. Set to 1 if calling with an unbound method to avoid the self argument.

Returns

a subset of config that only contains items compatible with the signature of func.

Return type

dict

Example

>>> # An example use case is to select a subset of of a config
>>> # that can be passed to some function as kwargs
>>> import ubelt as ub
>>> # Define a function with args that match some keys in a config.
>>> def func(a, e, f):
>>>     return a * e * f
>>> # Define a config that has a superset of items needed by the func
>>> config = {
...   'a': 2, 'b': 3, 'c': 7,
...   'd': 11, 'e': 13, 'f': 17,
... }
>>> # Call the function only with keys that are compatible
>>> func(**ub.compatible(config, func))
442

Example

>>> # Test case with kwargs
>>> import ubelt as ub
>>> def func(a, e, f, *args, **kwargs):
>>>     return a * e * f
>>> config = {
...   'a': 2, 'b': 3, 'c': 7,
...   'd': 11, 'e': 13, 'f': 17,
... }
>>> func(**ub.compatible(config, func))