I was expecting that the command
Z=[[141,163,127],[107,132,117],[85,116,120],[121,131,128]]
ZZ=[Z[i].insert(i,0) for i in range(len(Z))]will insert a 0 in rank 'i' for each element of Z but it returns [None, None, None, None].
Need help Thanks
As you correctly understood, insert modifies a list in-place, returning None.
An alternative is to create new lists, e.g. using slices of the old lists.
Here is one way to do that.
sage: Z = [[141, 163, 127], [107, 132, 117], [85, 116, 120], [121, 131, 128]]
sage: ZZ = [z[:i] + [0] + z[i:] for i, z in enumerate(Z)]
sage: ZZ
[[0, 141, 163, 127], [107, 0, 132, 117], [85, 116, 0, 120], [121, 131, 128, 0]]Nice. I have not thinked to this nice possibility.
Another option, which is just a small modification of the original code:
sage: Z = [[141,163,127],[107,132,117],[85,116,120],[121,131,128]]
sage: ZZ = copy(Z)
sage: [ZZ[i].insert(i,0) for i in range(len(ZZ))]; ZZ
[[0, 141, 163, 127], [107, 0, 132, 117], [85, 116, 0, 120], [121, 131, 128, 0]]Careful: use deepcopy instead of copy, otherwise Z ends up changed too.
Or write ZZ = [copy(z) for z in Z].
Yes, you are right. Thanks for the correction.
Asked: 4 years ago
Seen: 278 times
Last updated: Mar 25 '21
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I have understud.
insertmodifies directly Z