Problems with appending a list in Python

Question

I am recieving some POST data every three seconds (precisely 384 rows). These are stored in list called data. Then I would like to store them in list helper, which would be appended by data after every POST. For now I want to check the data in graph, so I need to convert helper into numpy array, which is called myArr.

data = json.loads(json_data)["data"] #I get some data
helper=[] #Then create list
helper.append(data) # And here I would like to add values to the end
myArr=np.asarray(helper)

self.send_response(200)
self.send_header("Content-type", "text/html")
self.end_headers()
self.wfile.write("") 


print (len(data))
print(type (data))
print (len(helper))
print(type (helper))
print (len(myArr))
print(type (myArr))
print data

But when I execute the code, the lenghts are not the same:

>>384
>><type 'list'>
>>1
>><type 'list'>
>>1
>><type 'numpy.ndarray'> 

And the list data content looks like this:

[[0.46124267578125, 0.0545654296875, 0.89111328125, 0.0, 0.0, 0.0, 0.0],
[0.46124267578125, 0.0545654296898, 0.89111328125, 0.0, 0.0, 0.0, 0.0],
[0.46124267578125, 0.0545654296875, 0.89111328125, 0.0, 0.0, 0.0, 0.0],
[0.4637451171875, 0.05804443359362, 0.8892822265625, 0.0, 0.0, 0.0, 0.0],
[0.4637451171875, 0.05804443359301, 0.8892822265625, 0.0, 0.0, 0.0, 0.0],
[0.4637451171875, 0.05804443359375, 0.8892822265625, 0.0, 0.0, 0.0, 0.0],
[etc.]]

I think there's just problem with dimensions of lists which I can not figure out.

Answer 1

You have a list to which you append another list, giving you a nested list with one item. Simple demo:

>>> data = [1,2,3]
>>> helper = []
>>> helper.append(data)
>>> helper
[[1, 2, 3]]
>>> len(helper)
1

I could not figure out from your question why you need the helper list at all, but to make a (shallow) copy issue helper = data[:] or helper.extend(data). Since I'm not sure where you are going from here I'll leave this answer at telling you why your helper list has one element, for now.