functools partial

The functools module is for higher-order functions: functions that act on or return other functions. In general, any callable object can be treated as a function for the purposes of this module.

Official python documentation

functools.partial Return a new partial object which when called will behave like func called with the positional arguments args and keyword arguments keywords.

• If more arguments are supplied to the call, they are appended to args.
• If additional keyword arguments are supplied, they extend and override keywords.

import functools
print(functools.partial.__doc__)

partial(func, *args, **keywords) - new function with partial application
    of the given arguments and keywords.

def foo(name):
  print(f'Inside foo : name = {name}')
foo('Krishan')

Inside foo : name = Krishan

Partial with default positional argument

foo_with_default = functools.partial(foo, 'Krishan')

foo_with_default()

Inside foo : name = Krishan

If name is passed again as keyword argument or positional arg, the decorated function will throw error.

foo_with_default(name = 'Ram')

---------------------------------------------------------------------------

TypeError: foo() got multiple values for argument 'name'

foo_with_default('Ram')

---------------------------------------------------------------------------

TypeError: foo() takes 1 positional argument but 2 were given

Partial with default Keyword argument

foo_with_default = functools.partial(foo, name = 'Krishan')

If name is passed again as a keyword argument, the kwargs gets updated before calling foo (the function being decorated.).

foo_with_default(name = 'Ram')

Inside foo : name = Ram

Same is not true for passing the argument as positional argument as positional arguments get appended which results in error.

foo_with_default('Ram')

---------------------------------------------------------------------------

TypeError: foo() takes 1 positional argument but 2 were given