argument-unpacking

python class that acts as mapping for **unpacking

由 流过昼夜 提交于 2020-01-05 03:12:08
问题 Without subclassing dict, what would a class need to be considered a mapping so that it can be passed to a method with ** from abc import ABCMeta class uobj: __metaclass__ = ABCMeta uobj.register(dict) def f(**k): return k o = uobj() f(**o) # outputs: f() argument after ** must be a mapping, not uobj At least to the point where it throws errors of missing functionality of mapping, so I can begin implementing. I reviewed emulating container types but simply defining magic methods has no effect

Python: Splat/unpack operator * in python cannot be used in an expression?

由 て烟熏妆下的殇ゞ 提交于 2019-12-28 04:22:08
问题 Does anybody know the reasoning as to why the unary ( * ) operator cannot be used in an expression involving iterators/lists/tuples? Why is it only limited to function unpacking? or am I wrong in thinking that? For example: >>> [1,2,3, *[4,5,6]] File "<stdin>", line 1 [1,2,3, *[4,5,6]] ^ SyntaxError: invalid syntax Why doesn't the * operator: [1, 2, 3, *[4, 5, 6]] give [1, 2, 3, 4, 5, 6] whereas when the * operator is used with a function call it does expand: f(*[4, 5, 6]) is equivalent to f

What does ** (double star/asterisk) and * (star/asterisk) do for parameters?

由 混江龙づ霸主 提交于 2019-12-25 08:07:36
问题 In the following method definitions, what does the * and ** do for param2 ? def foo(param1, *param2): def bar(param1, **param2): 回答1: The *args and **kwargs is a common idiom to allow arbitrary number of arguments to functions as described in the section more on defining functions in the Python documentation. The *args will give you all function parameters as a tuple: def foo(*args): for a in args: print(a) foo(1) # 1 foo(1,2,3) # 1 # 2 # 3 The **kwargs will give you all keyword arguments

What does the asterisk do in *a, b, c = line.split()?

由 ▼魔方 西西 提交于 2019-12-20 05:36:25
问题 Assume line is: "Chicago Sun 01:52" . What does *a, b, c = line.split() do? In particular, what is the significance of the asterisk? Edit: Upon testing it, it seems like "Chicago" , "Sun" and "01:52" are all stored in a , b and c . The asterisk seems to lead to "Chicago" being stored in a as the first element of a list. So, we have a = ["Chicago"] , b = "Sun" and c = "01:52" . Could anyone point to material on the functionality of the asterisk operator in this situation? 回答1: Splitting that

Unpack NumPy array by column

由 北慕城南 提交于 2019-12-19 05:14:50
问题 If I have a NumPy array, for example 5x3, is there a way to unpack it column by column all at once to pass to a function rather than like this: my_func(arr[:, 0], arr[:, 1], arr[:, 2]) ? Kind of like *args for list unpacking but by column. 回答1: You can unpack the transpose of the array in order to use the columns for your function arguments: my_func(*arr.T) Here's a simple example: >>> x = np.arange(15).reshape(5, 3) array([[ 0, 5, 10], [ 1, 6, 11], [ 2, 7, 12], [ 3, 8, 13], [ 4, 9, 14]]) Let

MATLAB: Accessing an element of a multidimensional array with a list

由 时间秒杀一切 提交于 2019-12-17 16:37:40
问题 I have a d-dimensional array, A , and vector inds with length equal to d. I would like to access the value of A at inds . Ideally, I'd do something like A(*inds) (borrowing the unpacking syntax from Python). I'm not sure how to do this in MATLAB. If I do A(inds) I actually get d separate values from A , which is not what I want. What I want is for element i of inds to be the ith parameter in the function call A (). 回答1: One solution is to create a comma-separated list out of your vector of

python class that acts as mapping for **unpacking

由 自闭症网瘾萝莉.ら 提交于 2019-12-17 02:44:13
问题 Without subclassing dict, what would a class need to be considered a mapping so that it can be passed to a method with ** from abc import ABCMeta class uobj: __metaclass__ = ABCMeta uobj.register(dict) def f(**k): return k o = uobj() f(**o) # outputs: f() argument after ** must be a mapping, not uobj At least to the point where it throws errors of missing functionality of mapping, so I can begin implementing. I reviewed emulating container types but simply defining magic methods has no effect

Python style for line length and format when unpacking many return values

由 亡梦爱人 提交于 2019-12-10 10:01:40
问题 Suppose that function some_descriptively_named_function returns a 4- tuple of 4 return parameters. I want to call some_descriptively_named_function , adhere to the 80-character line length limit, and unpack all 4 outputs each into a descriptively-named variable: some_desc_name1, some_desc_name2, some_desc_name3, some_desc_name4 = some_descriptively_named_function() One option is: some_desc_name1, some_desc_name2, some_desc_name3, some_desc_name4 = ( some_descriptively_named_function() ) With

Splatpacking versus array_values() to re-index an array with numeric keys

由 坚强是说给别人听的谎言 提交于 2019-12-10 00:34:49
问题 As of PHP7.4, there is a newly available technique to re-index an array with numeric keys. I'll call it " array re-packing " or maybe something fun like " splatpacking ". The simple process involves using the splat operator ( ... ) -- aka "spread operator" -- to unpack an array then fills a new array with with the contents. Comparison Code: (Demo) $array = [2 => 4, 5 => 3, "3" => null, -10.9 => 'foo']; var_export(array_values($array)); var_export([...$array]); Both will output: array ( 0 => 4

Splatpacking versus array_values() to re-index an array with numeric keys

由 ￣綄美尐妖づ 提交于 2019-12-04 22:07:51
As of PHP7.4, there is a newly available technique to re-index an array with numeric keys. I'll call it " array re-packing " or maybe something fun like " splatpacking ". The simple process involves using the splat operator ( ... ) -- aka " spread operator " -- to unpack an array then fills a new array with with the contents. Comparison Code: ( Demo ) $array = [2 => 4, 5 => 3, "3" => null, -10.9 => 'foo']; var_export(array_values($array)); var_export([...$array]); Both will output: array ( 0 => 4, 1 => 3, 2 => NULL, 3 => 'foo', ) Again, the splatpacking technique is strictly limited to arrays
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