CODEWITHSUNDEEP
pythonpython-2.x
calvin
calvin

Reputation: 2945

what's the usage of `in dic` here

I am reading Python source codes, and I find this code in Python-2.7.10/Lib/multiprocessing/managers.py.

I just wondering what's the usage of % (meth, meth) in dic here, because I think % will first associate the string, and exec always returns None

def MakeProxyType(name, exposed, _cache={}):
    '''
    Return an proxy type whose methods are given by `exposed`
    '''
    exposed = tuple(exposed)
    try:
        return _cache[(name, exposed)]
    except KeyError:
        pass

    dic = {}

    for meth in exposed:
        exec '''def %s(self, *args, **kwds):
        return self._callmethod(%r, args, kwds)''' % (meth, meth) in dic

    ProxyType = type(name, (BaseProxy,), dic)
    ProxyType._exposed_ = exposed
    _cache[(name, exposed)] = ProxyType
    return ProxyType

Upvotes: 0

Views: 37

Answers (1)

AKX
AKX

Reputation: 169298

You can rephrase it as

code = '''def %s(self, *args, **kwds):
        return self._callmethod(%r, args, kwds)''' % (meth, meth)
exec code in dic

which in turn uses the exec ... in ... form:

In all cases, if the optional parts [in ...] are omitted, the code is executed in the current scope. If only the first expression after in is specified, it should be a dictionary, which will be used for both the global and the local variables. If two expressions are given, they are used for the global and local variables, respectively. If provided, locals can be any mapping object. Remember that at module level, globals and locals are the same dictionary. If two separate objects are given as globals and locals, the code will be executed as if it were embedded in a class definition.

That is, the code will be executed within the to-be-created proxy type's class variable dictionary.

Upvotes: 3

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