将项目附加到 python 中的列表列表 [英] Appending items to a list of lists in python
问题描述
我对列表索引很生气,无法解释我做错了什么.
我有一段代码,我想在其中创建一个列表列表,每个列表都包含我从 csv
读取的相同电路参数(电压、电流等)的值代码>文件看起来像这样:
样品,V1,I1,V2,I20, 3, 0.01, 3, 0.021, 3, 0.01, 3, 0.03
等等.我想要的是创建一个列表,例如以 [[V1], [I1]] 的形式包含 V1 和 I1(但我想以交互方式选择),所以:
[[3,3], [0.01, 0.01]]
我使用的代码是这样的:
plot_data = [[]]*len(positions)对于阅读器中的行:对于范围内的位置(len(位置)):值 = 浮点数(行[位置[位置]])plot_data[地方].append(value)
plot_data
是包含所有值的列表,而 positions
是一个列表,其中包含我想从 .csv 复制的列的索引
文件.问题是,如果我在 shell 中尝试命令,似乎可以工作,但是如果我运行脚本而不是将每个值附加到正确的子列表中,它会将所有值附加到所有列表中,因此我获得 2(或更多)) 相同的列表.
Python 列表是可变对象,这里:
plot_data = [[]] * len(positions)
您正在重复相同的列表 len(positions)
次.
列表中的每个列表都是对同一对象的引用.你修改一个,你会看到所有的修改.
如果你想要不同的列表,你可以这样做:
plot_data = [[] for _ in position]
例如:
<预><代码>>>>pd = [[] for _ in range(3)]>>>PD[[], [], []]>>>pd[0].append(1)>>>PD[[1], [], []]I'm getting mad with list indexes, and can't explain what I'm doing wrong.
I have this piece of code in which I want to create a list of lists, each one containing values of the same circuit parameter (voltage, current etc..) that I'm reading from a csv
file that looks like this:
Sample, V1, I1, V2, I2
0, 3, 0.01, 3, 0.02
1, 3, 0.01, 3, 0.03
And so on. What I want is to create a list that for example contains V1 and I1 (but I want to chose interactively) in the form [[V1], [I1]], so:
[[3,3], [0.01, 0.01]]
The code that I'm using is this:
plot_data = [[]]*len(positions)
for row in reader:
for place in range(len(positions)):
value = float(row[positions[place]])
plot_data[place].append(value)
plot_data
is the list that contains all the values, while positions
is a list with the indexes of the columns that I want to copy from the .csv
file. The problem is that if I try the commands in the shell, seems to work, but if I run the script instead of appending each value to the proper sub-list, it appends all values to all lists, so I obtain 2 (or more) identical lists.
Python lists are mutable objects and here:
plot_data = [[]] * len(positions)
you are repeating the same list len(positions)
times.
>>> plot_data = [[]] * 3
>>> plot_data
[[], [], []]
>>> plot_data[0].append(1)
>>> plot_data
[[1], [1], [1]]
>>>
Each list in your list is a reference to the same object. You modify one, you see the modification in all of them.
If you want different lists, you can do this way:
plot_data = [[] for _ in positions]
for example:
>>> pd = [[] for _ in range(3)]
>>> pd
[[], [], []]
>>> pd[0].append(1)
>>> pd
[[1], [], []]
这篇关于将项目附加到 python 中的列表列表的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!