【python】__import__

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函數定義

__import__(name, globals={}, locals={}, fromlist=[], level=-1) -> moduleImport a module. Because this function is meant for use by the Pythoninterpreter and not for general use it is better to useimportlib.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 fromlistshould be a list of names to emulate ``from name import ...‘‘, or anempty 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 whenfromlist is not empty.  Level is used to determine whether to perform absolute or relative imports.  -1 is the original strategy of attemptingboth absolute and relative imports, 0 is absolute, a positive numberis the number of parent directories to search relative to the current module.    

name:引用模組名稱，如‘sys’, ‘libs/module.a‘
fromlist:子模組列表，如果name是a.b的格式，則必須把b加入fromlist中

用途

• 動態匯入模組

例子

import osdef test():    datetime = __import__(‘datetime‘)    print datetime.datetime.now()    a = __import__("module.module_a", globals={}, locals={}, fromlist=["module_a"], level=-1)    print a.sub(x, y)test()

調用不同目錄的模組

• 應該先sys.path.append(模組所在路徑)，然後再用相對路徑引用

例：
在下面這個例子中，由於celery調用，運行路徑跟當前路徑不同，直接引用module.module_a會報錯：無法找到該模組，同時如果__import__的第一個參數用絕對路徑，會報錯：不可使用檔案名稱引用
正確方法就是先在系統路徑中加入當前路徑，然後用相對路徑引用

from celery import Celeryimport osimport syscurrent_path = os.path.dirname(os.path.realpath(__file__))sys.path.append(current_path)app = Celery(‘tasks‘, backend=‘amqp‘, broker=‘amqp://test:[email protected]/testhost‘)@app.taskdef add(x, y):    a = __import__("module.module_a", globals={}, locals={}, fromlist=["module_a"], level=-1)    print a.add(x, y)

【python】__import__