如果名称存储在变量中，则在Python中访问模块级函数

Question

What is the best way to use a function at the top of a module if do not know the name of the object in advance: The function might depend on user input and hence its name is stored in a variable.

One solution uses eval() : For example, in ScipyCookbook/SignalSmooth: smooth() (also referenced in an answer to StackOverflow: Python Smooth Time Series Data )

import numpy  
window = 'hanning'
w = eval('numpy.'+window+'(11)')

will be equivalent to

w = numpy.hanning(11)

However, is there a better method than using fragile/potentially dangerous eval ?

For instance, wouldn't using vars()

w = vars(numpy)[window](11)

be preferred? Any better/more pythonic ideas?

Answer 1

You should use a dictionary mapping the valid window function names to the actual functions:

windows = {"bartlett": numpy.bartlett,
           "blackman": numpy.blackman,
           "hamming": numpy.hamming,
           "hanning": numpy.hanning,
           "kaiser": numpy.kaiser}

If you use eval() , the user is basically allowed to execute arbitrary code.

The variant

w = vars(numpy)[window](11)

is definitely better than using eval() , but it still does not make sure the function the user selected makes sense in the given context. (And usually, you'd use getattr() for this instead.)

Answer 2

A module's functions are attributes of the module, so you can do:

window = "hanning"
getattr(numpy, window)(11)

vars() is also fine.