嵌套子对象/链接属性上的 getattr 和 setattr？
getattr and setattr on nested subobjects / chained properties?
我有一个对象 (Person)，它有多个子对象 (Pet, Residence) 作为属性。我希望能够像这样动态设置这些子对象的属性：
class Person(object):
def __init__(self):
self.pet = Pet()
self.residence = Residence()
class Pet(object):
def __init__(self,name='Fido',species='Dog'):
self.name = name
self.species = species
class Residence(object):
def __init__(self,type='House',sqft=None):
self.type = type
self.sqft=sqft
if __name__=='__main__':
p=Person()
setattr(p,'pet.name','Sparky')
setattr(p,'residence.type','Apartment')
print p.__dict__
目前我得到错误的输出：{'pet': <__main__.Pet object at 0x10c5ec050>, 'residence': <__main__.Residence object at 0x10c5ec0d0>, 'pet.name': 'Sparky', 'residence.type': 'Apartment'}
如您所见，不是在 Person 的 Pet 子对象上设置 name 属性，而是在 Person。
不能指定person.pet到setattr()，因为不同的子对象会通过同一个方法设置，解析一些文本，填充对象属性if/when 已找到相关密钥。
是否有 easy/builtin 方法来完成此操作？
或者我可能需要编写一个递归函数来解析字符串并多次调用 getattr() 直到找到必要的子对象，然后在找到的子对象上调用 setattr() ?
好的，所以在输入问题时，我想到了如何执行此操作，而且它似乎工作正常。这是我想出的：
def set_attribute(obj, path_string, new_value):
parts = path_string.split('.')
final_attribute_index = len(parts)-1
current_attribute = obj
i = 0
for part in parts:
new_attr = getattr(current_attribute, part, None)
if current_attribute is None:
print 'Error %s not found in %s' % (part, current_attribute)
break
if i == final_attribute_index:
setattr(current_attribute, part, new_value)
current_attribute = new_attr
i+=1
def get_attribute(obj, path_string):
parts = path_string.split('.')
final_attribute_index = len(parts)-1
current_attribute = obj
i = 0
for part in parts:
new_attr = getattr(current_attribute, part, None)
if current_attribute is None:
print 'Error %s not found in %s' % (part, current_attribute)
return None
if i == final_attribute_index:
return getattr(current_attribute, part)
current_attribute = new_attr
i += 1
我想这解决了我的问题，但我仍然很好奇是否有更好的方法来做到这一点？
我觉得这在 OOP 和 python 中一定很常见，所以我很惊讶 gatattr 和 setattr 本身不支持它。
您可以使用 functools.reduce:
import functools
def rsetattr(obj, attr, val):
pre, _, post = attr.rpartition('.')
return setattr(rgetattr(obj, pre) if pre else obj, post, val)
# using wonder's beautiful simplification:
def rgetattr(obj, attr, *args):
def _getattr(obj, attr):
return getattr(obj, attr, *args)
return functools.reduce(_getattr, [obj] + attr.split('.'))
rgetattr 和 rsetattr 是 getattr 和 setattr 的直接替代品，
它也可以处理带点的 attr 字符串。
import functools
class Person(object):
def __init__(self):
self.pet = Pet()
self.residence = Residence()
class Pet(object):
def __init__(self,name='Fido',species='Dog'):
self.name = name
self.species = species
class Residence(object):
def __init__(self,type='House',sqft=None):
self.type = type
self.sqft=sqft
def rsetattr(obj, attr, val):
pre, _, post = attr.rpartition('.')
return setattr(rgetattr(obj, pre) if pre else obj, post, val)
def rgetattr(obj, attr, *args):
def _getattr(obj, attr):
return getattr(obj, attr, *args)
return functools.reduce(_getattr, [obj] + attr.split('.'))
if __name__=='__main__':
p = Person()
print(rgetattr(p, 'pet.favorite.color', 'calico'))
# 'calico'
try:
# Without a default argument, `rgetattr`, like `getattr`, raises
# AttributeError when the dotted attribute is missing
print(rgetattr(p, 'pet.favorite.color'))
except AttributeError as err:
print(err)
# 'Pet' object has no attribute 'favorite'
rsetattr(p, 'pet.name', 'Sparky')
rsetattr(p, 'residence.type', 'Apartment')
print(p.__dict__)
print(p.pet.name)
# Sparky
print(p.residence.type)
# Apartment
一个parent和一个child:
if __name__=='__main__':
p = Person()
parent, child = 'pet.name'.split('.')
setattr(getattr(p, parent), child, 'Sparky')
parent, child = 'residence.type'.split('.')
setattr(getattr(p, parent), child, 'Sparky')
print p.__dict__
对于这个特定用例，这比其他答案更简单。
我根据 ubntu 的回答做了一个简单的版本，叫做 magicattr，它也可以通过解析和遍历 ast 来处理 attrs、列表和字典。
例如，class：
class Person:
settings = {
'autosave': True,
'style': {
'height': 30,
'width': 200
},
'themes': ['light', 'dark']
}
def __init__(self, name, age, friends):
self.name = name
self.age = age
self.friends = friends
bob = Person(name="Bob", age=31, friends=[])
jill = Person(name="Jill", age=29, friends=[bob])
jack = Person(name="Jack", age=28, friends=[bob, jill])
你可以做到
# Nothing new
assert magicattr.get(bob, 'age') == 31
# Lists
assert magicattr.get(jill, 'friends[0].name') == 'Bob'
assert magicattr.get(jack, 'friends[-1].age') == 29
# Dict lookups
assert magicattr.get(jack, 'settings["style"]["width"]') == 200
# Combination of lookups
assert magicattr.get(jack, 'settings["themes"][-2]') == 'light'
assert magicattr.get(jack, 'friends[-1].settings["themes"][1]') == 'dark'
# Setattr
magicattr.set(bob, 'settings["style"]["width"]', 400)
assert magicattr.get(bob, 'settings["style"]["width"]') == 400
# Nested objects
magicattr.set(bob, 'friends', [jack, jill])
assert magicattr.get(jack, 'friends[0].friends[0]') == jack
magicattr.set(jill, 'friends[0].age', 32)
assert bob.age == 32
它也不会让 you/someone 调用函数或赋值，因为它不使用 eval 或允许 Assign/Call 个节点。
with pytest.raises(ValueError) as e:
magicattr.get(bob, 'friends = [1,1]')
# Nice try, function calls are not allowed
with pytest.raises(ValueError):
magicattr.get(bob, 'friends.pop(0)')
unutbu 的回答 () 有一个 "bug"。在 getattr() 失败并被 default 替换后，它继续调用 default 上的 getattr。
示例：rgetattr(object(), "nothing.imag", 1) 在我看来应该等于 1，但 returns 0:
getattr(object(), 'nothing', 1) == 1.getattr(1, 'imag', 1) == 0（因为 1 是实数，没有复数分量）。
解决方案
我在第一个缺少的属性处将 rgetattr 修改为 return default：
import functools
DELIMITER = "."
def rgetattr(obj, path: str, *default):
"""
:param obj: Object
:param path: 'attr1.attr2.etc'
:param default: Optional default value, at any point in the path
:return: obj.attr1.attr2.etc
"""
attrs = path.split(DELIMITER)
try:
return functools.reduce(getattr, attrs, obj)
except AttributeError:
if default:
return default[0]
raise
我就是喜欢递归函数
def rgetattr(obj,attr):
_this_func = rgetattr
sp = attr.split('.',1)
if len(sp)==1:
l,r = sp[0],''
else:
l,r = sp
obj = getattr(obj,l)
if r:
obj = _this_func(obj,r)
return obj
以及基于 jimbo1qaz 答案的简单易懂的三行代码，减少到极限：
def rgetattr(obj, path, default):
try:
return functools.reduce(getattr, path.split(), obj)
except AttributeError:
return default
用法：
>>> class O(object):
... pass
... o = O()
... o.first = O()
... o.first.second = O()
... o.first.second.third = 42
... rgetattr(o, 'first second third', None)
42
请记住，"space" 不是此用例的典型分隔符。
这应该是
def getNestedAttr(obj,nestedParam):
next = obj
for p in nestedParam.split('.'):
next = getattr(next,p)
return next
class Issue : pass
issue = Issue()
issue.status = Issue()
issue.status.name = "Hello"
getattr(issue,'status.name')
'''
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'Issue' object has no attribute 'status.name'
'''
getNestedAttr(issue,'status.name')
#'Hello'
简单的解决方案
这里有一些类似于 ChaimG 的答案，但它适用于任意数量的案例。但是，它只支持获取属性，不支持设置属性。
requested_attr = 'pet.name'
parent = Person()
sub_names = requested_attr.split('.')
sub = None
for sub_name in sub_names:
try:
sub = parent.__getattribute__(sub_name)
parent = sub
except AttributeError:
raise Exception("The panel doesn't have an attribute that matches your request!")
pets_name = sub
对于开箱即用的解决方案，您可以使用 operator.attrgetter:
from operator import attrgetter
attrgetter(dotted_path)(obj)
感谢您接受上面的回答。这很有帮助。
如果有人想扩展 hasattr 的使用，请使用以下代码：
def rhasattr(obj, attr):
_nested_attrs = attr.split(".")
_curr_obj = obj
for _a in _nested_attrs[:-1]:
if hasattr(_curr_obj, _a):
_curr_obj = getattr(_curr_obj, _a)
else:
return False
return hasattr(_curr_obj, _nested_attrs[-1])
我有一个对象 (Person)，它有多个子对象 (Pet, Residence) 作为属性。我希望能够像这样动态设置这些子对象的属性：
class Person(object):
def __init__(self):
self.pet = Pet()
self.residence = Residence()
class Pet(object):
def __init__(self,name='Fido',species='Dog'):
self.name = name
self.species = species
class Residence(object):
def __init__(self,type='House',sqft=None):
self.type = type
self.sqft=sqft
if __name__=='__main__':
p=Person()
setattr(p,'pet.name','Sparky')
setattr(p,'residence.type','Apartment')
print p.__dict__
目前我得到错误的输出：{'pet': <__main__.Pet object at 0x10c5ec050>, 'residence': <__main__.Residence object at 0x10c5ec0d0>, 'pet.name': 'Sparky', 'residence.type': 'Apartment'}
如您所见，不是在 Person 的 Pet 子对象上设置 name 属性，而是在 Person。
不能指定
person.pet到setattr()，因为不同的子对象会通过同一个方法设置，解析一些文本，填充对象属性if/when 已找到相关密钥。是否有 easy/builtin 方法来完成此操作？
或者我可能需要编写一个递归函数来解析字符串并多次调用
getattr()直到找到必要的子对象，然后在找到的子对象上调用setattr()?
好的，所以在输入问题时，我想到了如何执行此操作，而且它似乎工作正常。这是我想出的：
def set_attribute(obj, path_string, new_value):
parts = path_string.split('.')
final_attribute_index = len(parts)-1
current_attribute = obj
i = 0
for part in parts:
new_attr = getattr(current_attribute, part, None)
if current_attribute is None:
print 'Error %s not found in %s' % (part, current_attribute)
break
if i == final_attribute_index:
setattr(current_attribute, part, new_value)
current_attribute = new_attr
i+=1
def get_attribute(obj, path_string):
parts = path_string.split('.')
final_attribute_index = len(parts)-1
current_attribute = obj
i = 0
for part in parts:
new_attr = getattr(current_attribute, part, None)
if current_attribute is None:
print 'Error %s not found in %s' % (part, current_attribute)
return None
if i == final_attribute_index:
return getattr(current_attribute, part)
current_attribute = new_attr
i += 1
我想这解决了我的问题，但我仍然很好奇是否有更好的方法来做到这一点？
我觉得这在 OOP 和 python 中一定很常见，所以我很惊讶 gatattr 和 setattr 本身不支持它。
您可以使用 functools.reduce:
import functools
def rsetattr(obj, attr, val):
pre, _, post = attr.rpartition('.')
return setattr(rgetattr(obj, pre) if pre else obj, post, val)
# using wonder's beautiful simplification:
def rgetattr(obj, attr, *args):
def _getattr(obj, attr):
return getattr(obj, attr, *args)
return functools.reduce(_getattr, [obj] + attr.split('.'))
rgetattr 和 rsetattr 是 getattr 和 setattr 的直接替代品，
它也可以处理带点的 attr 字符串。
import functools
class Person(object):
def __init__(self):
self.pet = Pet()
self.residence = Residence()
class Pet(object):
def __init__(self,name='Fido',species='Dog'):
self.name = name
self.species = species
class Residence(object):
def __init__(self,type='House',sqft=None):
self.type = type
self.sqft=sqft
def rsetattr(obj, attr, val):
pre, _, post = attr.rpartition('.')
return setattr(rgetattr(obj, pre) if pre else obj, post, val)
def rgetattr(obj, attr, *args):
def _getattr(obj, attr):
return getattr(obj, attr, *args)
return functools.reduce(_getattr, [obj] + attr.split('.'))
if __name__=='__main__':
p = Person()
print(rgetattr(p, 'pet.favorite.color', 'calico'))
# 'calico'
try:
# Without a default argument, `rgetattr`, like `getattr`, raises
# AttributeError when the dotted attribute is missing
print(rgetattr(p, 'pet.favorite.color'))
except AttributeError as err:
print(err)
# 'Pet' object has no attribute 'favorite'
rsetattr(p, 'pet.name', 'Sparky')
rsetattr(p, 'residence.type', 'Apartment')
print(p.__dict__)
print(p.pet.name)
# Sparky
print(p.residence.type)
# Apartment
一个parent和一个child:
if __name__=='__main__':
p = Person()
parent, child = 'pet.name'.split('.')
setattr(getattr(p, parent), child, 'Sparky')
parent, child = 'residence.type'.split('.')
setattr(getattr(p, parent), child, 'Sparky')
print p.__dict__
对于这个特定用例，这比其他答案更简单。
我根据 ubntu 的回答做了一个简单的版本，叫做 magicattr，它也可以通过解析和遍历 ast 来处理 attrs、列表和字典。
例如，class：
class Person:
settings = {
'autosave': True,
'style': {
'height': 30,
'width': 200
},
'themes': ['light', 'dark']
}
def __init__(self, name, age, friends):
self.name = name
self.age = age
self.friends = friends
bob = Person(name="Bob", age=31, friends=[])
jill = Person(name="Jill", age=29, friends=[bob])
jack = Person(name="Jack", age=28, friends=[bob, jill])
你可以做到
# Nothing new
assert magicattr.get(bob, 'age') == 31
# Lists
assert magicattr.get(jill, 'friends[0].name') == 'Bob'
assert magicattr.get(jack, 'friends[-1].age') == 29
# Dict lookups
assert magicattr.get(jack, 'settings["style"]["width"]') == 200
# Combination of lookups
assert magicattr.get(jack, 'settings["themes"][-2]') == 'light'
assert magicattr.get(jack, 'friends[-1].settings["themes"][1]') == 'dark'
# Setattr
magicattr.set(bob, 'settings["style"]["width"]', 400)
assert magicattr.get(bob, 'settings["style"]["width"]') == 400
# Nested objects
magicattr.set(bob, 'friends', [jack, jill])
assert magicattr.get(jack, 'friends[0].friends[0]') == jack
magicattr.set(jill, 'friends[0].age', 32)
assert bob.age == 32
它也不会让 you/someone 调用函数或赋值，因为它不使用 eval 或允许 Assign/Call 个节点。
with pytest.raises(ValueError) as e:
magicattr.get(bob, 'friends = [1,1]')
# Nice try, function calls are not allowed
with pytest.raises(ValueError):
magicattr.get(bob, 'friends.pop(0)')
unutbu 的回答 (getattr() 失败并被 default 替换后，它继续调用 default 上的 getattr。
示例：rgetattr(object(), "nothing.imag", 1) 在我看来应该等于 1，但 returns 0:
getattr(object(), 'nothing', 1)== 1.getattr(1, 'imag', 1)== 0（因为 1 是实数，没有复数分量）。
解决方案
我在第一个缺少的属性处将 rgetattr 修改为 return default：
import functools
DELIMITER = "."
def rgetattr(obj, path: str, *default):
"""
:param obj: Object
:param path: 'attr1.attr2.etc'
:param default: Optional default value, at any point in the path
:return: obj.attr1.attr2.etc
"""
attrs = path.split(DELIMITER)
try:
return functools.reduce(getattr, attrs, obj)
except AttributeError:
if default:
return default[0]
raise
我就是喜欢递归函数
def rgetattr(obj,attr):
_this_func = rgetattr
sp = attr.split('.',1)
if len(sp)==1:
l,r = sp[0],''
else:
l,r = sp
obj = getattr(obj,l)
if r:
obj = _this_func(obj,r)
return obj
以及基于 jimbo1qaz 答案的简单易懂的三行代码，减少到极限：
def rgetattr(obj, path, default):
try:
return functools.reduce(getattr, path.split(), obj)
except AttributeError:
return default
用法：
>>> class O(object):
... pass
... o = O()
... o.first = O()
... o.first.second = O()
... o.first.second.third = 42
... rgetattr(o, 'first second third', None)
42
请记住，"space" 不是此用例的典型分隔符。
这应该是
def getNestedAttr(obj,nestedParam):
next = obj
for p in nestedParam.split('.'):
next = getattr(next,p)
return next
class Issue : pass
issue = Issue()
issue.status = Issue()
issue.status.name = "Hello"
getattr(issue,'status.name')
'''
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'Issue' object has no attribute 'status.name'
'''
getNestedAttr(issue,'status.name')
#'Hello'
简单的解决方案
这里有一些类似于 ChaimG 的答案，但它适用于任意数量的案例。但是，它只支持获取属性，不支持设置属性。
requested_attr = 'pet.name'
parent = Person()
sub_names = requested_attr.split('.')
sub = None
for sub_name in sub_names:
try:
sub = parent.__getattribute__(sub_name)
parent = sub
except AttributeError:
raise Exception("The panel doesn't have an attribute that matches your request!")
pets_name = sub
对于开箱即用的解决方案，您可以使用 operator.attrgetter:
from operator import attrgetter
attrgetter(dotted_path)(obj)
感谢您接受上面的回答。这很有帮助。
如果有人想扩展 hasattr 的使用，请使用以下代码：
def rhasattr(obj, attr):
_nested_attrs = attr.split(".")
_curr_obj = obj
for _a in _nested_attrs[:-1]:
if hasattr(_curr_obj, _a):
_curr_obj = getattr(_curr_obj, _a)
else:
return False
return hasattr(_curr_obj, _nested_attrs[-1])