Python在import时遇到的惨案

__import__(name[, globals[, locals[, fromlist[, level]]]])

Note

This is an advanced function that is not needed in everyday Python programming.

This function is invoked by the import statement. It can be replaced (by importing the __builtin__ module and assigning to__builtin__.__import__) in order to change semantics of the import statement, but nowadays it is usually simpler to use import hooks (see PEP 302). Direct use of __import__() is rare, except in cases where you want to import a module whose name is only known at runtime.

The function imports the module name, potentially using the given globals and locals to determine how to interpret the name in a package context. The fromlist gives the names of objects or submodules that should be imported from the module given by name. The standard implementation does not use its locals argument at all, and uses its globals only to determine the package context of the importstatement.

level specifies whether to use absolute or relative imports. The default is -1 which indicates both absolute and relative imports will be attempted. 0 means only perform absolute imports. Positive values for level indicate the number of parent directories to search relative to the directory of the module calling __import__().

When the name variable is of the form package.module, normally, the top-level package (the name up till the first dot) is returned, not the module named by name. However, when a non-empty fromlist argument is given, the module named by name is returned.

For example, the statement import spam results in bytecode resembling the following code:

spam = __import__('spam', globals(), locals(), [], -1)
The statement import spam.ham results in this call:

spam = __import__('spam.ham', globals(), locals(), [], -1)
Note how __import__() returns the toplevel module here because this is the object that is bound to a name by the import statement.