Python之動態調用函數

                                     Python之動態調用函數

     在Java中，動態調用可通過反射機制實現。Python中，也可通過__import__(filename) + getattr()實現。

1、__import__(filename)：動態加載

python中，一般通過from XX import XX引入模塊，當調用模塊不確定時，可通過__import__()動態載入，通過“字符串”函數名動態調用函數。

def __import__(name, globals=None, locals=None, fromlist=(), level=0): # real signature unknown; restored from __doc__
    """
    __import__(name, globals=None, locals=None, fromlist=(), level=0) -> module
    
    Import a module. Because this function is meant for use by the Python
    interpreter and not for general use it is better to use
    importlib.import_module() to programmatically import a module.
    
    The globals argument is only used to determine the context;
    they are not modified.  The locals argument is unused.  The fromlist
    should be a list of names to emulate ``from name import ...'', or an
    empty list to emulate ``import name''.
    When importing a module from a package, note that __import__('A.B', ...)
    returns package A when fromlist is empty, but its submodule B when
    fromlist is not empty.  Level is used to determine whether to perform 
    absolute or relative imports. 0 is absolute while a positive number
    is the number of parent directories to search relative to the current module.
    """
    pass

name: 模塊名

 

2、getattr() ：返回一個對象屬性值

def getattr(object, name, default=None): # known special case of getattr
    """
    getattr(object, name[, default]) -> value
    
    Get a named attribute from an object; getattr(x, 'y') is equivalent to x.y.
    When a default argument is given, it is returned when the attribute doesn't
    exist; without it, an exception is raised in that case.
    """
    pass

object：對象屬性的值

name:  類屬性名對應的字符串

default： name對應屬性不存在，給定default參數則返回default，沒有default，則直接有AttributeError異常

 

3、例子

動態引入運行：#1 動態載入模塊 ；#2 獲取類對象； #3 獲取函數對象，func(para_comm) 動態調用函數。

注：

載入模塊時，會碰見"No module named XXX" ,  注意path搜索模塊路徑的配置。

獲取對象時，也可通過  hasattr(calssname, attributename) 判斷屬性是否存在， 避免AttributeError的異常。

import_module = __import__(moudlename)   # 1
b = getattr(import_module, classname)() # 2
func = getattr(b, methodname)          # 3
res = func(para_comm)   # para_comm 傳入參數