nested-lists

Python append() vs. + operator on lists, why do these give different results?

由 北慕城南 提交于 2019-11-26 10:15:18
Why do these two operations ( append() resp. + ) give different results? >>> c = [1, 2, 3] >>> c [1, 2, 3] >>> c += c >>> c [1, 2, 3, 1, 2, 3] >>> c = [1, 2, 3] >>> c.append(c) >>> c [1, 2, 3, [...]] >>> In the last case there's actually an infinite recursion. c[-1] and c are the same. Why is it different with the + operation? Abel To explain "why": The + operation adds the array elements to the original array. The array.append operation inserts the array (or any object) into the end of the original array, which results in a reference to self in that spot (hence the infinite recursion). The

Converting nested list to dataframe

由 允我心安 提交于 2019-11-26 07:33:46
问题 The goal is to convert a nested list which sometimes contain missing records into a data frame. An example of the structure when there are missing records is: str(mylist) List of 3 $ :List of 7 ..$ Hit : chr \"True\" ..$ Project: chr \"Blue\" ..$ Year : chr \"2011\" ..$ Rating : chr \"4\" ..$ Launch : chr \"26 Jan 2012\" ..$ ID : chr \"19\" ..$ Dept : chr \"1, 2, 4\" $ :List of 2 ..$ Hit : chr \"False\" ..$ Error: chr \"Record not found\" $ :List of 7 ..$ Hit : chr \"True\" ..$ Project: chr \

why can't I change only a single element in a nested list in Python [duplicate]

由 南笙酒味 提交于 2019-11-26 04:55:53
问题 This question already has answers here : List of lists changes reflected across sublists unexpectedly (13 answers) Closed last year . I just met something really strange of Python: >>> out=[[0]*3]*3 >>> out [[0, 0, 0], [0, 0, 0], [0, 0, 0]] >>> out[0][1] 0 >>> out[0][1]=9 >>> out [[0, 9, 0], [0, 9, 0], [0, 9, 0]] well, obviously, what I want is : [[0, 9, 0], [0, 0, 0], [0, 0, 0]] isn\'t strange? I\'m not very familiar with Python, but Python always impresses me with its intuitive behavior.

Python append() vs. + operator on lists, why do these give different results?

由 与世无争的帅哥 提交于 2019-11-26 01:51:48
问题 Why do these two operations ( append() resp. + ) give different results? >>> c = [1, 2, 3] >>> c [1, 2, 3] >>> c += c >>> c [1, 2, 3, 1, 2, 3] >>> c = [1, 2, 3] >>> c.append(c) >>> c [1, 2, 3, [...]] >>> In the last case there\'s actually an infinite recursion. c[-1] and c are the same. Why is it different with the + operation? 回答1: To explain "why": The + operation adds the array elements to the original array. The array.append operation inserts the array (or any object) into the end of the

Proper way to make HTML nested list?

由 自作多情 提交于 2019-11-25 23:04:43
问题 The W3 docs have a nested list example prefixed by DEPRECATED EXAMPLE: , but they never corrected it with a non-deprecated example, nor explained exactly what is wrong with the example. So which of these ways is the correct way to write an HTML list? Option 1 : the nested <ul> is a child of the parent <ul> <ul> <li>List item one</li> <li>List item two with subitems:</li> <ul> <li>Subitem 1</li> <li>Subitem 2</li> </ul> <li>Final list item</li> </ul> Option 2 : the nested <ul> is a child of

List of lists changes reflected across sublists unexpectedly

由 耗尽温柔 提交于 2019-11-25 22:09:27
问题 I needed to create a list of lists in Python, so I typed the following: myList = [[1] * 4] * 3 The list looked like this: [[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]] Then I changed one of the innermost values: myList[0][0] = 5 Now my list looks like this: [[5, 1, 1, 1], [5, 1, 1, 1], [5, 1, 1, 1]] which is not what I wanted or expected. Can someone please explain what\'s going on, and how to get around it? 回答1: When you write [x]*3 you get, essentially, the list [x, x, x] . That is, a list
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