为什么在函数参数中使用常规？

Question

I was wondering why many functions - especially in numpy - utilize tuples as function parameters?

eg:

a = numpy.ones( (10, 5) )

What could possibly be the use for that? Why not simply have something such as the following, since clearly the first parameters will always denote the size of the array?

a = numpy.ones(10, 5)

Is it because there might be additional parameters, such as dtype? even if so,

a = numpy.ones(10, 5, dtype=numpy.int)

seems much cleaner to me, than using the convoluted tuple convention.

Thanks for your replies

Answer 1

Because you want to be able to do:

a = numpy.ones(other_array.shape)

and other_array.shape is a tuple. There are a few functions that are not consistent with this and work as you've described, eg numpy.random.rand()

Answer 2

I think one of the benefits of this is that it can lead to consistency between the various methods. I'm not that familiar with numpy, but it would seem to me the first use case that comes to mind is if numpy can return the size of an array, that size, as one variable, can be directly passed to another numpy method, without having to know anything about the internals of how that size item is built.

The other part of it is that size of an array may have two components but it's discussed as one value, not as two.

Answer 3

My guess: this is because in functions like np.ones , shape can be passed as a keyword argument when it's a single value. Try

np.ones(dtype=int, shape=(2, 3))

and notice that you get the same value as you would have gotten from np.ones((2, 3), dtype=int) .

[This works in Python more generally:

>>> def f(a, b):
...     return a + b
... 
>>> f(b="foo", a="bar")
'barfoo'

]

Answer 4

In order for python to tell the difference between foo(1, 2) , foo(1, dtype='int') and foo(1, 2, dtype='int') you would have to use keyword-only arguments which weren't formally introduced until python 3. It is possible to use **kargs to implement keyword only arguments in python 2.x but it's unnatural and does not seem Pythonic. I think for that reason array does not allow array(1, 2) but reshape(1, 2) is ok because reshape does not take any keywords.