functools — Higher order functions and operations on callable objects¶New in version 2.5:
New in version 2.5.
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.
The functools module defines the following functions:
functools.partial(func[,*args][, **keywords])¶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.
Roughly equivalent to:
def partial(func, *args, **keywords):
def newfunc(*fargs, **fkeywords):
newkeywords = keywords.copy()
newkeywords.update(fkeywords)
return func(*(args + fargs), **newkeywords)
newfunc.func = func
newfunc.args = args
newfunc.keywords = keywords
return newfunc
The partial() is used for partial function application which “freezes”
some portion of a function’s arguments and/or keywords resulting in a new object
with a simplified signature. For example, partial() can be used to create
a callable that behaves like the int() function where the base argument
defaults to two:
>>> from functools import partial
>>> basetwo = partial(int, base=2)
>>> basetwo.__doc__ = 'Convert base 2 string to an int.'
>>> basetwo('10010')
18
functools.update_wrapper(wrapper, wrapped[, assigned][, updated])¶Update a wrapper function to look like the wrapped function. The optional arguments are tuples to specify which attributes of the original function are assigned directly to the matching attributes on the wrapper function and which attributes of the wrapper function are updated with the corresponding attributes from the original function. The default values for these arguments are the module level constants WRAPPER_ASSIGNMENTS (which assigns to the wrapper function’s __name__, __module__ and __doc__, the documentation string) and WRAPPER_UPDATES (which updates the wrapper function’s __dict__, i.e. the instance dictionary).
The main intended use for this function is in decorator functions which wrap the decorated function and return the wrapper. If the wrapper function is not updated, the metadata of the returned function will reflect the wrapper definition rather than the original function definition, which is typically less than helpful.
functools.wraps(wrapped[, assigned][, updated])¶This is a convenience function for invoking partial(update_wrapper,
wrapped=wrapped, assigned=assigned, updated=updated) as a function decorator
when defining a wrapper function. For example:
>>> from functools import wraps
>>> def my_decorator(f):
... @wraps(f)
... def wrapper(*args, **kwds):
... print 'Calling decorated function'
... return f(*args, **kwds)
... return wrapper
...
>>> @my_decorator
... def example():
... """Docstring"""
... print 'Called example function'
...
>>> example()
Calling decorated function
Called example function
>>> example.__name__
'example'
>>> example.__doc__
'Docstring'
Without the use of this decorator factory, the name of the example function
would have been 'wrapper', and the docstring of the original example()
would have been lost.
partial Objects¶partial objects are callable objects created by partial(). They
have three read-only attributes:
partial.func¶A callable object or function. Calls to the partial object will be
forwarded to func with new arguments and keywords.
partial.args¶The leftmost positional arguments that will be prepended to the positional
arguments provided to a partial object call.
partial objects are like function objects in that they are
callable, weak referencable, and can have attributes. There are some important
differences. For instance, the __name__ and __doc__ attributes
are not created automatically. Also, partial objects defined in
classes behave like static methods and do not transform into bound methods
during instance attribute look-up.