Creating a namedtuple from a list

问题:

Consider a list variable t

In [55]: t
Out[55]:
['1.423',
 '0.046',
 '98.521',
 '0.010',
 '0.000',
 '0.000',
 '5814251520.0',
 '769945600.0',
 '18775908352.0',
 '2.45024350208e+11',
 '8131.903',
 '168485.073',
 '0.0',
 '0.0',
 '0.022',
 '372.162',
 '1123.041',
 '1448.424']

Now consider a namedtuple 'Point':

Point = namedtuple('Point', 'usr sys idl wai hiq siq  used  buff  cach  free
    read  writ recv  send majpf minpf alloc  vmfree')

How do we convert the variable t to a Point? The most obvious (to me anyways..) approach - of just providing the list as a constructor argument - does not work:

In [57]: Point(t)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-57-635019d8b551> in <module>()
----> 1 Point(t)

TypeError: __new__() takes exactly 19 arguments (2 given)

回答1:

Use Point(*t) to expand the contents of t as arguments to the Point constructor.

回答2:

More efficient solution: Use the special _make alternate constructor to directly construct the namedtuple from an arbitrary iterable without creating additional intermediate tuples (as star-unpacking to the main constructor requires). Runs faster, less memory churn:

Point._make(t)

Despite the name, _make is part of the public API; it's named with a leading underscore to avoid conflicts with field names (which aren't allowed to begin with an underscore).