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() 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.

  • arg (object, default=None) – some value
  • *args – ignored
  • **kwargs – ignored

arg: the same value

Return type:


xdoctest -m ubelt.util_func identity


>>> import ubelt as ub
>>> ub.identity(42)
>>> ub.identity(42, 42)
>>> ub.identity()
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.

  • self (object) – instance to inject a function into
  • func (func) – 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.


>>> class Foo(object):
>>>     def bar(self):
>>>         return 'bar'
>>> def baz(self):
>>>     return 'baz'
>>> self = Foo()
>>> assert self.bar() == 'bar'
>>> assert not hasattr(self, 'baz')
>>> inject_method(self, baz)
>>> assert not hasattr(Foo, 'baz'), 'should only change one instance'
>>> assert self.baz() == 'baz'
>>> inject_method(self, baz, 'bar')
>>> assert self.bar() == 'baz'