对于“ Python开发人员基础”课程的未来学生，我们准备了一篇有用的文章的翻译。
functools , , .
, functools partial, «» . , , . , , .
partial
partial myfunc(). , show_details() func, args partial .
import functools
def myfunc(a, b=2):
"""Docstring for myfunc()."""
print '\tcalled myfunc with:', (a, b)
return
def show_details(name, f, is_partial=False):
"""Show details of a callable object."""
print '%s:' % name
print '\tobject:', f
if not is_partial:
print '\t__name__:', f.__name__
print '\t__doc__', repr(f.__doc__)
if is_partial:
print '\tfunc:', f.func
print '\targs:', f.args
print '\tkeywords:', f.keywords
return
show_details('myfunc', myfunc)
myfunc('a', 3)
print
p1 = functools.partial(myfunc, b=4)
show_details('partial with named default', p1, True)
p1('default a')
p1('override b', b=5)
print
p2 = functools.partial(myfunc, 'default a', b=99)
show_details('partial with defaults', p2, True)
p2()
p2(b='override b')
print
print 'Insufficient arguments:'
p1() partial a, .
$ python functools_partial.py
myfunc:
object: <function myfunc at 0x100468c08>
__name__: myfunc
__doc__ 'Docstring for myfunc().'
called myfunc with: ('a', 3)
partial with named default:
object: <functools.partial object at 0x10046b050>
__doc__ 'partial(func, *args, **keywords) - new function with partial
application\n of the given arguments and keywords.\n'
func: <function myfunc at 0x100468c08>
args: ()
keywords: {'b': 4}
called myfunc with: ('default a', 4)
called myfunc with: ('override b', 5)
partial with defaults:
object: <functools.partial object at 0x10046b0a8>
__doc__ 'partial(func, *args, **keywords) - new function with partial
application\n of the given arguments and keywords.\n'
func: <function myfunc at 0x100468c08>
args: ('default a',)
keywords: {'b': 99}
called myfunc with: ('default a', 99)
called myfunc with: ('default a', 'override b')
Insufficient arguments:
Traceback (most recent call last):
File "functools_partial.py", line 49, in <module>
p1()
TypeError: myfunc() takes at least 1 argument (1 given)update_wrapper
partial _name_ _doc_ , . update_wrapper() partial .
import functools
def myfunc(a, b=2):
"""Docstring for myfunc()."""
print '\tcalled myfunc with:', (a, b)
return
def show_details(name, f):
"""Show details of a callable object."""
print '%s:' % name
print '\tobject:', f
print '\t__name__:',
try:
print f.__name__
except AttributeError:
print '(no __name__)'
print '\t__doc__', repr(f.__doc__)
print
return
show_details('myfunc', myfunc)
p1 = functools.partial(myfunc, b=4)
show_details('raw wrapper', p1)
print 'Updating wrapper:'
print '\tassign:', functools.WRAPPER_ASSIGNMENTS
print '\tupdate:', functools.WRAPPER_UPDATES
print
functools.update_wrapper(p1, myfunc)
show_details('updated wrapper', p1), wrapper functools.WRAPPER_ASSIGNMENTS, functools.WRAPPER_UPDATES , .
$ python functools_update_wrapper.py
myfunc:
object: <function myfunc at 0x100468c80>
__name__: myfunc
__doc__ 'Docstring for myfunc().'
raw wrapper:
object: <functools.partial object at 0x10046c0a8>
__name__: (no __name__)
__doc__ 'partial(func, *args, **keywords) - new function with partial
application\n of the given arguments and keywords.\n'
Updating wrapper:
assign: ('__module__', '__name__', '__doc__')
update: ('__dict__',)
updated wrapper:
object: <functools.partial object at 0x10046c0a8>
__name__: myfunc
__doc__ 'Docstring for myfunc().'Partial , , .
import functools
class MyClass(object):
"""Demonstration class for functools"""
def meth1(self, a, b=2):
"""Docstring for meth1()."""
print '\tcalled meth1 with:', (self, a, b)
return
def meth2(self, c, d=5):
"""Docstring for meth2"""
print '\tcalled meth2 with:', (self, c, d)
return
wrapped_meth2 = functools.partial(meth2, 'wrapped c')
functools.update_wrapper(wrapped_meth2, meth2)
def __call__(self, e, f=6):
"""Docstring for MyClass.__call__"""
print '\tcalled object with:', (self, e, f)
return
def show_details(name, f):
"""Show details of a callable object."""
print '%s:' % name
print '\tobject:', f
print '\t__name__:',
try:
print f.__name__
except AttributeError:
print '(no __name__)'
print '\t__doc__', repr(f.__doc__)
return
o = MyClass()
show_details('meth1 straight', o.meth1)
o.meth1('no default for a', b=3)
print
p1 = functools.partial(o.meth1, b=4)
functools.update_wrapper(p1, o.meth1)
show_details('meth1 wrapper', p1)
p1('a goes here')
print
show_details('meth2', o.meth2)
o.meth2('no default for c', d=6)
print
show_details('wrapped meth2', o.wrapped_meth2)
o.wrapped_meth2('no default for c', d=6)
print
show_details('instance', o)
o('no default for e')
print
p2 = functools.partial(o, f=7)
show_details('instance wrapper', p2)
p2('e goes here')partial .
$ python functools_method.py
meth1 straight:
object: <bound method MyClass.meth1 of <__main__.MyClass object at
0x10046a3d0>>
__name__: meth1
__doc__ 'Docstring for meth1().'
called meth1 with: (<__main__.MyClass object at 0x10046a3d0>, 'no d
efault for a', 3)
meth1 wrapper:
object: <functools.partial object at 0x10046c158>
__name__: meth1
__doc__ 'Docstring for meth1().'
called meth1 with: (<__main__.MyClass object at 0x10046a3d0>, 'a go
es here', 4)
meth2:
object: <bound method MyClass.meth2 of <__main__.MyClass object at
0x10046a3d0>>
__name__: meth2
__doc__ 'Docstring for meth2'
called meth2 with: (<__main__.MyClass object at 0x10046a3d0>, 'no d
efault for c', 6)
wrapped meth2:
object: <functools.partial object at 0x10046c0a8>
__name__: meth2
__doc__ 'Docstring for meth2'
called meth2 with: ('wrapped c', 'no default for c', 6)
instance:
object: <__main__.MyClass object at 0x10046a3d0>
__name__: (no __name__)
__doc__ 'Demonstration class for functools'
called object with: (<__main__.MyClass object at 0x10046a3d0>, 'no
default for e', 6)
instance wrapper:
object: <functools.partial object at 0x10046c1b0>
__name__: (no __name__)
__doc__ 'partial(func, *args, **keywords) - new function with parti
al application\n of the given arguments and keywords.\n'
called object with: (<__main__.MyClass object at 0x10046a3d0>, 'e g
oes here', 7)wraps
, «» .
import functools
def show_details(name, f):
"""Show details of a callable object."""
print '%s:' % name
print '\tobject:', f
print '\t__name__:',
try:
print f.__name__
except AttributeError:
print '(no __name__)'
print '\t__doc__', repr(f.__doc__)
print
return
def simple_decorator(f):
@functools.wraps(f)
def decorated(a='decorated defaults', b=1):
print '\tdecorated:', (a, b)
print '\t',
f(a, b=b)
return
return decorated
def myfunc(a, b=2):
print '\tmyfunc:', (a,b)
return
show_details('myfunc', myfunc)
myfunc('unwrapped, default b')
myfunc('unwrapped, passing b', 3)
print
wrapped_myfunc = simple_decorator(myfunc)
show_details('wrapped_myfunc', wrapped_myfunc)
wrapped_myfunc()
wrapped_myfunc('args to decorated', 4)Functools wraps(), update_wrapper() .
Python 2 _cmp_(), -1, 0 1 , , , . Python 2.1 , _lt_(), _le_(), _eq_(), _ne_(), _gt_() _ge_(), . Python 3 cmp() , functools , Python 2, Python 3.
, . , , . total_ordering() , , .
import functools
import inspect
from pprint import pprint
@functools.total_ordering
class MyObject(object):
def __init__(self, val):
self.val = val
def __eq__(self, other):
print ' testing __eq__(%s, %s)' % (self.val, other.val)
return self.val == other.val
def __gt__(self, other):
print ' testing __gt__(%s, %s)' % (self.val, other.val)
return self.val > other.val
print 'Methods:\n'
pprint(inspect.getmembers(MyObject, inspect.ismethod))
a = MyObject(1)
b = MyObject(2)
print '\nComparisons:'
for expr in [ 'a < b', 'a <= b', 'a == b', 'a >= b', 'a > b' ]:
print '\n%-6s:' % expr
result = eval(expr)
print ' result of %s: %s' % (expr, result) _eq_() . , .
$ python functools_total_ordering.py
Methods:
[('__eq__', <unbound method MyObject.__eq__>),
('__ge__', <unbound method MyObject.__ge__>),
('__gt__', <unbound method MyObject.__gt__>),
('__init__', <unbound method MyObject.__init__>),
('__le__', <unbound method MyObject.__le__>),
('__lt__', <unbound method MyObject.__lt__>)]
Comparisons:
a < b :
testing __gt__(1, 2)
testing __eq__(1, 2)
result of a < b: True
a <= b:
testing __gt__(1, 2)
result of a <= b: True
a == b:
testing __eq__(1, 2)
result of a == b: False
a >= b:
testing __gt__(1, 2)
testing __eq__(1, 2)
result of a >= b: False
a > b :
testing __gt__(1, 2)
result of a > b: False Python 3, cmp sort(). Python 2, , cmp_to_key() , , .
import functools
class MyObject(object):
def __init__(self, val):
self.val = val
def __str__(self):
return 'MyObject(%s)' % self.val
def compare_obj(a, b):
"""Old-style comparison function.
"""
print 'comparing %s and %s' % (a, b)
return cmp(a.val, b.val)
# Make a key function using cmp_to_key()
get_key = functools.cmp_to_key(compare_obj)
def get_key_wrapper(o):
"""Wrapper function for get_key to allow for print statements.
"""
new_key = get_key(o)
print 'key_wrapper(%s) -> %s' % (o, new_key)
return new_key
objs = [ MyObject(x) for x in xrange(5, 0, -1) ]
for o in sorted(objs, key=get_key_wrapper):
print o: , cmp_to_key() , , , .
, sorted() get_key_wrapper() . , cmp_to_key(), , functools, . , – .
$ python functools_cmp_to_key.py
key_wrapper(MyObject(5)) -> <functools.K object at 0x100466558>
key_wrapper(MyObject(4)) -> <functools.K object at 0x100466590>
key_wrapper(MyObject(3)) -> <functools.K object at 0x1004665c8>
key_wrapper(MyObject(2)) -> <functools.K object at 0x100466600>
key_wrapper(MyObject(1)) -> <functools.K object at 0x100466638>
comparing MyObject(4) and MyObject(5)
comparing MyObject(3) and MyObject(4)
comparing MyObject(2) and MyObject(3)
comparing MyObject(1) and MyObject(2)
MyObject(1)
MyObject(2)
MyObject(3)
MyObject(4)
MyObject(5)"Python Developer. Basic". "Pytest: " .