update explanation of the slicing element string

[liconlab]

To slice the last three characters, one should use element[-3 : ], which might be a more universal way for any string with length >=3.
Using element[3:6] refers to the 4th to the 6th characters by its literal meaning.

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[ldko]

Hi @zhaophotonicslab, congratulations on opening your first Software Carpentry PR! You make a valid point here that if you want a general slice of the last 3 characters of a string you should use [-3 : ]. However, I think where you are making this change, the negative indexing has not yet been introduced. Since in the case of "oxygen", element[3:6] does also give you the last three characters, I suggest we leave that as is, and then add a final part to the Challenge (after the solution for explaining what element[1:-1] does) that asks something like "How can we rewrite the slice for getting the last three characters of element, so that it works on any character string of at least three characters"?

[liconlab]

Dear Lauren, Thanks for your prompt response. It is a good idea to put it as an exercise to the Challenge. I agree with you that introducing negative indexing may bring confusions or take more time to explain to students.

…

________________________________ From: Lauren Ko <notifications@github.com> Sent: Thursday, April 2, 2020 8:17 AM To: swcarpentry/python-novice-inflammation <python-novice-inflammation@noreply.github.com> Cc: zhaophotonicslab <zhao.qiancheng@outlook.com>; Mention <mention@noreply.github.com> Subject: Re: [swcarpentry/python-novice-inflammation] update explanation of the slicing element string (#818) Hi @zhaophotonicslab<https://github.com/zhaophotonicslab>, congratulations on opening your first Software Carpentry PR! You make a valid point here that if you want a general slice of the last 3 characters of a string you should use [-3 : ]. However, I think where you are making this change, the negative indexing has not yet been introduced. Since in the case of "oxygen", element[3:6] does also give you the last three characters, I suggest we leave that as is, and then add a final part to the Challenge (after the solution for explaining what element[1:-1] does) that asks something like "How can we rewrite the slice for getting the last three characters of element, so that it works on any character string of at least three characters"? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub<#818 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AORJ7NDPWK2QA3Z4DNCKDYDRKSUBRANCNFSM4LZ62PAQ>.

[ldko]

Hi @zhaophotonicslab, since negative indexing is brought up in the Challenge shortly after where you have made an edit, after that point, we have a good opportunity to show the way you suggest of getting the last three characters. Would you like to modify this Pull Request to change line 508 back to what it was then ask "How can we rewrite the slice for getting the last three characters of element, so it will work on any character string at least three characters in length"? around line 550?

[liconlab]

Hi Lauren, Thanks for the suggestions. I agree it is better to put it in the challenge part. I have modified my branch as suggested. Do I need to create a new pull request? The commit ID to my own branch is 1334999 I might have also accidently committed to swcarpentry gh-page branch. If I did, please ignore that. Thanks again for your response. From: Lauren Ko <notifications@github.com> Sent: Friday, April 3, 2020 8:26 AM To: swcarpentry/python-novice-inflammation <python-novice-inflammation@noreply.github.com> Cc: zhaophotonicslab <zhao.qiancheng@outlook.com>; Mention <mention@noreply.github.com> Subject: Re: [swcarpentry/python-novice-inflammation] update explanation of the slicing element string (#818) Hi @zhaophotonicslab<https://github.com/zhaophotonicslab>, since negative indexing is brought up in the Challenge shortly after where you have made an edit, after that point, we have a good opportunity to show the way you suggest of getting the last three characters. Would you like to modify this Pull Request to change line 508 back to what it was then ask "How can we rewrite the slice for getting the last three characters of element, so it will work on any character string at least three characters in length"? around line 550? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub<#818 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AORJ7NBZ5AOME27X3FWJJR3RKX5ZJANCNFSM4LZ62PAQ>.

[ldko]

@zhaophotonicslab thank you so much for the quick followup and changes! There is no need to open a new pull request. This one will be fine to continue with. These changes look good but need a few minor changes before we can merge them.

[liconlab]

Hi @IDKo, Thanks for pointing out the errors. I have fixed the syntax errors as suggested. From: Lauren Ko <notifications@github.com> Sent: Friday, April 3, 2020 10:15 AM To: swcarpentry/python-novice-inflammation <python-novice-inflammation@noreply.github.com> Cc: zhaophotonicslab <zhao.qiancheng@outlook.com>; Mention <mention@noreply.github.com> Subject: Re: [swcarpentry/python-novice-inflammation] update explanation of the slicing element string (#818) @ldko requested changes on this pull request. @zhaophotonicslab<https://github.com/zhaophotonicslab> thank you so much for the quick followup and changes! There is no need to open a new pull request. This one will be fine to continue with. These changes look good but need a few minor changes before we can merge them.

________________________________ In _episodes/02-numpy.md<#818 (comment)>:

@@ -546,6 +546,20 @@ which is the average inflammation per patient across all days.

> Creates a substring from index 1 up to (not including) the final index, > effectively removing the first and last letters from 'oxygen' {: .solution} +> +> How can we rewrite the slice for getting the last three characters of `element` does, +> so it will work on any character string at least three characters in length. +> +> > ## Solution +> > ~~~ +> > print('last three characters:', element[-3:]) +> ~~~ +> {: .language-python} There is a slight syntax error here that is causing a failed check on the Pull Request. I think we can fix it with another greater than symbol on the two above lines:

> ~~~ > {: .language-python}

________________________________ In _episodes/02-numpy.md<#818 (comment)>:

@@ -546,6 +546,20 @@ which is the average inflammation per patient across all days.

> Creates a substring from index 1 up to (not including) the final index, > effectively removing the first and last letters from 'oxygen' {: .solution} +> +> How can we rewrite the slice for getting the last three characters of `element` does, +> so it will work on any character string at least three characters in length. Can you remove the word "does" on line 550 and change the period (.) to a question mark (?) at the end of line 551? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub<#818 (review)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AORJ7NDP3Y622ZKALPW53YLRKYKSTANCNFSM4LZ62PAQ>.

[liconlab]

That’s a good idea. Thanks to @maxim-belkin and @IDKo. The changes have been made. From: Lauren Ko <notifications@github.com> Sent: Friday, April 3, 2020 11:08 AM To: swcarpentry/python-novice-inflammation <python-novice-inflammation@noreply.github.com> Cc: zhaophotonicslab <zhao.qiancheng@outlook.com>; Mention <mention@noreply.github.com> Subject: Re: [swcarpentry/python-novice-inflammation] update explanation of the slicing element string (#818) @ldko commented on this pull request.

________________________________ In _episodes/02-numpy.md<#818 (comment)>:

@@ -546,6 +546,20 @@ which is the average inflammation per patient across all days.

> Creates a substring from index 1 up to (not including) the final index, > effectively removing the first and last letters from 'oxygen' {: .solution} +> +> How can we rewrite the slice for getting the last three characters of `element`, +> so it will work on any character string at least three characters in length? I think that change is fine to make. It might be nice having hi as an example, since it will show learners that it doesn't error to take a slice bigger than the string. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub<#818 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AORJ7NHSLJ3YXR5ZZNEUHSLRKYQYBANCNFSM4LZ62PAQ>.

[ldko]

I think this looks great! Thanks very much, @zhaophotonicslab !

[maxim-belkin]

Looks great! Thank you @zhaophotonicslab! Great job, Lauren!