導入協議：sh如何創建導入的包裝函數？

Question

發現sh module整合的bash（外殼）到蟒蛇後，我使用它幾乎在大多數情況下，而不是短shell腳本（SH基本上是類固醇子，和這種類型的集成允許有很「Python的bash腳本「）。的確，我可以做類似

from sh import ifconfig 
print(ifconfig("wlan0")) 

現在ifconfig不是sh模塊的一部分。顯然，這個功能是動態構建的。現在我非常好奇這是如何完成的。

所以，我的問題是它是如何工作的？

起初，我認爲有一個PEP描述這種做法作爲一種「協議」（類似於__enter__()或next()）。但我還沒有找到任何PEP解釋這一點。

Answer 1

從SH源代碼：

# this is a thin wrapper around THIS module (we patch sys.modules[__name__]). 
# this is in the case that the user does a "from sh import whatever" 
# in other words, they only want to import certain programs, not the whole 
# system PATH worth of commands. in this case, we just proxy the 
# import lookup to our Environment class 
class SelfWrapper(ModuleType): 
    def __init__(self, self_module, baked_args={}): 
     # this is super ugly to have to copy attributes like this, 
     # but it seems to be the only way to make reload() behave 
     # nicely. if i make these attributes dynamic lookups in 
     # __getattr__, reload sometimes chokes in weird ways... 
     for attr in ["__builtins__", "__doc__", "__name__", "__package__"]: 
      setattr(self, attr, getattr(self_module, attr, None)) 

     # python 3.2 (2.7 and 3.3 work fine) breaks on osx (not ubuntu) 
     # if we set this to None. and 3.3 needs a value for __path__ 
     self.__path__ = [] 
     self.self_module = self_module 
     self.env = Environment(globals(), baked_args) 

    def __setattr__(self, name, value): 
     if hasattr(self, "env"): self.env[name] = value 
     ModuleType.__setattr__(self, name, value) 

    def __getattr__(self, name): 
     if name == "env": raise AttributeError 
     return self.env[name] 

    # accept special keywords argument to define defaults for all operations 
    # that will be processed with given by return SelfWrapper 
    def __call__(self, **kwargs): 
     return SelfWrapper(self.self_module, kwargs) 

幾行後，在不主要

# we're being imported from somewhere 
else: 
    self = sys.modules[__name__] 
    sys.modules[__name__] = SelfWrapper(self)