Re: Cutting slices
Am 05.03.23 um 23:43 schrieb Stefan Ram: The following behaviour of Python strikes me as being a bit "irregular". A user tries to chop of sections from a string, but does not use "split" because the separator might become more complicated so that a regular expression will be required to find it. OK, so if you want to use an RE for splitting, can you not use re.split() ? It basically works like the built-in splitting in AWK >>> s='alphaAbetaBgamma' >>> import re >>> re.split(r'A|B|C', s) ['alpha', 'beta', 'gamma'] >>> Christian -- https://mail.python.org/mailman/listinfo/python-list
RE: Cutting slices
I am not commenting on the technique or why it is chosen just the part where the last search looks for a non-existent period: s = 'alpha.beta.gamma' ... s[ 11: s.find( '.', 11 )] What should "find" do if it hits the end of a string without finding the period you claim is a divider? Could that be why gamma got truncated? Unless you can arrange for a terminal period, maybe you can reconsider the approach. -Original Message- From: Python-list On Behalf Of aapost Sent: Sunday, March 5, 2023 6:00 PM To: python-list@python.org Subject: Re: Cutting slices On 3/5/23 17:43, Stefan Ram wrote: >The following behaviour of Python strikes me as being a bit >"irregular". A user tries to chop of sections from a string, >but does not use "split" because the separator might become >more complicated so that a regular expression will be required >to find it. But for now, let's use a simple "find": > > |>>> s = 'alpha.beta.gamma' > |>>> s[ 0: s.find( '.', 0 )] > |'alpha' > |>>> s[ 6: s.find( '.', 6 )] > |'beta' > |>>> s[ 11: s.find( '.', 11 )] > |'gamm' > |>>> > >. The user always inserted the position of the previous find plus >one to start the next "find", so he uses "0", "6", and "11". >But the "a" is missing from the final "gamma"! > >And it seems that there is no numerical value at all that >one can use for "n" in "string[ 0: n ]" to get the whole >string, isn't it? > > I would agree with 1st part of the comment. Just noting that string[11:], string[11:None], as well as string[11:16] work ... as well as string[11:324242]... lol.. -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Re: Cutting slices
On 6/03/23 11:43 am, Stefan Ram wrote: A user tries to chop of sections from a string, but does not use "split" because the separator might become more complicated so that a regular expression will be required to find it. What's wrong with re.split() in that case? -- Greg -- https://mail.python.org/mailman/listinfo/python-list
Re: Cutting slices
On 2023-03-06 00:28, dn via Python-list wrote:
On 06/03/2023 11.59, aapost wrote:
On 3/5/23 17:43, Stefan Ram wrote:
The following behaviour of Python strikes me as being a bit
"irregular". A user tries to chop of sections from a string,
but does not use "split" because the separator might become
more complicated so that a regular expression will be required
to find it. But for now, let's use a simple "find":
|>>> s = 'alpha.beta.gamma'
|>>> s[ 0: s.find( '.', 0 )]
|'alpha'
|>>> s[ 6: s.find( '.', 6 )]
|'beta'
|>>> s[ 11: s.find( '.', 11 )]
|'gamm'
|>>>
. The user always inserted the position of the previous find plus
one to start the next "find", so he uses "0", "6", and "11".
But the "a" is missing from the final "gamma"!
And it seems that there is no numerical value at all that
one can use for "n" in "string[ 0: n ]" to get the whole
string, isn't it?
I would agree with 1st part of the comment.
Just noting that string[11:], string[11:None], as well as string[11:16]
work ... as well as string[11:324242]... lol..
To expand on the above, answering the OP's second question: the numeric
value is len( s ).
If the repetitive process is required, try a loop like:
>>> start_index = 11 #to cure the issue-raised
>>> try:
... s[ start_index:s.index( '.', start_index ) ]
... except ValueError:
... s[ start_index:len( s ) ]
...
'gamma'
Somewhat off-topic, but...
When there was a discussion about a None-coalescing operator, I thought
that it would've been nice if .find and .rfind returned None instead of -1.
There have been times when I've wanted to find the next space (or
whatever) and have it return the length of the string if absent. That
could've been accomplished with:
s.find(' ', pos) ?? len(s)
Other times I've wanted it to return -1. That could've been accomplished
with:
s.find(' ', pos) ?? -1
(There's a place in the re module where .rfind returning -1 is just the
right value.)
In this instance, slicing with None as the end is just what's wanted.
Ah, well...
--
https://mail.python.org/mailman/listinfo/python-list
Re: Cutting slices
On 05/03/2023 22:59, aapost wrote: On 3/5/23 17:43, Stefan Ram wrote: The following behaviour of Python strikes me as being a bit "irregular". A user tries to chop of sections from a string, but does not use "split" because the separator might become more complicated so that a regular expression will be required to find it. But for now, let's use a simple "find": |>>> s = 'alpha.beta.gamma' |>>> s[ 0: s.find( '.', 0 )] |'alpha' |>>> s[ 6: s.find( '.', 6 )] |'beta' |>>> s[ 11: s.find( '.', 11 )] |'gamm' |>>> . The user always inserted the position of the previous find plus one to start the next "find", so he uses "0", "6", and "11". But the "a" is missing from the final "gamma"! And it seems that there is no numerical value at all that one can use for "n" in "string[ 0: n ]" to get the whole string, isn't it? The final `find` returns -1 because there is no separator after 'gamma'. So you are asking for s[ 11 : -1] which correctly returns 'gamm'. You need to test for this condition. Alternatively you could ensure that there is a final separator: s = 'alpha.beta.gamma.' but you would still need to test when the string was exhausted. Best wishes Rob Cliffe -- https://mail.python.org/mailman/listinfo/python-list
Re: Cutting slices
On 06/03/2023 11.59, aapost wrote: On 3/5/23 17:43, Stefan Ram wrote: The following behaviour of Python strikes me as being a bit "irregular". A user tries to chop of sections from a string, but does not use "split" because the separator might become more complicated so that a regular expression will be required to find it. But for now, let's use a simple "find": |>>> s = 'alpha.beta.gamma' |>>> s[ 0: s.find( '.', 0 )] |'alpha' |>>> s[ 6: s.find( '.', 6 )] |'beta' |>>> s[ 11: s.find( '.', 11 )] |'gamm' |>>> . The user always inserted the position of the previous find plus one to start the next "find", so he uses "0", "6", and "11". But the "a" is missing from the final "gamma"! And it seems that there is no numerical value at all that one can use for "n" in "string[ 0: n ]" to get the whole string, isn't it? I would agree with 1st part of the comment. Just noting that string[11:], string[11:None], as well as string[11:16] work ... as well as string[11:324242]... lol.. To expand on the above, answering the OP's second question: the numeric value is len( s ). If the repetitive process is required, try a loop like: >>> start_index = 11 #to cure the issue-raised >>> try: ... s[ start_index:s.index( '.', start_index ) ] ... except ValueError: ... s[ start_index:len( s ) ] ... 'gamma' However, if the objective is to split, then use the function built for the purpose: >>> s.split( "." ) ['alpha', 'beta', 'gamma'] (yes, the OP says this won't work - but doesn't show why) If life must be more complicated, but the next separator can be predicted, then its close-relative is partition(). NB can use both split() and partition() on the sub-strings produced by an earlier split() or ... ie there may be no reason to work strictly from left to right - can't really help with this because the information above only shows multiple "." characters, and not how multiple separators might be interpreted. A straight-line approach might be to use maketrans() and translate() to convert all the separators to a single character, eg white-space, which can then be split using any of the previously-mentioned methods. If the problem is sufficiently complicated and the OP is prepared to go whole-hog, then PSL's tokenize library or various parser libraries may be worth consideration... -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: Cutting slices
On 3/5/23 17:43, Stefan Ram wrote: The following behaviour of Python strikes me as being a bit "irregular". A user tries to chop of sections from a string, but does not use "split" because the separator might become more complicated so that a regular expression will be required to find it. But for now, let's use a simple "find": |>>> s = 'alpha.beta.gamma' |>>> s[ 0: s.find( '.', 0 )] |'alpha' |>>> s[ 6: s.find( '.', 6 )] |'beta' |>>> s[ 11: s.find( '.', 11 )] |'gamm' |>>> . The user always inserted the position of the previous find plus one to start the next "find", so he uses "0", "6", and "11". But the "a" is missing from the final "gamma"! And it seems that there is no numerical value at all that one can use for "n" in "string[ 0: n ]" to get the whole string, isn't it? I would agree with 1st part of the comment. Just noting that string[11:], string[11:None], as well as string[11:16] work ... as well as string[11:324242]... lol.. -- https://mail.python.org/mailman/listinfo/python-list
