在python中，我必须实例化某个类，知道它在字符串中的名称，但这个类“生活”在一个动态导入的模块中。示例如下:
loader类脚本:
import sys
class loader:
def __init__(self, module_name, class_name): # both args are strings
try:
__import__(module_name)
modul = sys.modules[module_name]
instance = modul.class_name() # obviously this doesn't works, here is my main problem!
except ImportError:
# manage import error
some-dynamically-loaded-module脚本:
class myName:
# etc...
我使用这种安排使加载器类使用任何动态加载模块，遵循动态加载模块中的某些预定义行为…
当前回答
你可以使用getattr
getattr(module, class_name)
访问类。更完整的代码:
module = __import__(module_name)
class_ = getattr(module, class_name)
instance = class_()
正如下面提到的，我们可以使用importlib
import importlib
module = importlib.import_module(module_name)
class_ = getattr(module, class_name)
instance = class_()
其他回答
你可以使用getattr
getattr(module, class_name)
访问类。更完整的代码:
module = __import__(module_name)
class_ = getattr(module, class_name)
instance = class_()
正如下面提到的，我们可以使用importlib
import importlib
module = importlib.import_module(module_name)
class_ = getattr(module, class_name)
instance = class_()
使用getattr从字符串中的名称中获取属性。换句话说，获取实例为
instance = getattr(modul, class_name)()
复制粘贴代码片段:
import importlib
def str_to_class(module_name, class_name):
"""Return a class instance from a string reference"""
try:
module_ = importlib.import_module(module_name)
try:
class_ = getattr(module_, class_name)()
except AttributeError:
logging.error('Class does not exist')
except ImportError:
logging.error('Module does not exist')
return class_ or None
如果你想从foo中得到这句话。Bar import foo2来动态加载，你应该这样做
foo = __import__("foo")
bar = getattr(foo,"bar")
foo2 = getattr(bar,"foo2")
instance = foo2()
从上面的例子中，我不能完全达到我的用例，但Ahmad给了我最接近的(谢谢)。对于那些将来读到这篇文章的人来说，下面是对我有用的代码。
def get_class(fully_qualified_path, module_name, class_name, *instantiation):
"""
Returns an instantiated class for the given string descriptors
:param fully_qualified_path: The path to the module eg("Utilities.Printer")
:param module_name: The module name eg("Printer")
:param class_name: The class name eg("ScreenPrinter")
:param instantiation: Any fields required to instantiate the class
:return: An instance of the class
"""
p = __import__(fully_qualified_path)
m = getattr(p, module_name)
c = getattr(m, class_name)
instance = c(*instantiation)
return instance
