[newbie] troubles with tuples

[Jean Dupont]

I'm looking at the way to address tuples
e.g.
tup2 = (1, 2, 3, 4, 5, 6, 7 );

As I found out indices start with 0 in Python, so
tup2[0] gives me 1, the first element in the tuple as expected
tup2[1] gives me 2, the second element in the tuple as expected
now here comes what surprises me:
tup2[0:1] does not give me the expected (1,2) but (2,)

what is the reason for this and how then should one get the first and the second element of a tuple? Or the 3rd until the 5th?

thanks in advance and kind regards,

jean

 

[Asaf Las]

I'm looking at the way to address tuples

e.g.
tup2 = (1, 2, 3, 4, 5, 6, 7 );
As I found out indices start with 0 in Python, so
tup2[0] gives me 1, the first element in the tuple as expected
tup2[1] gives me 2, the second element in the tuple as expected
now here comes what surprises me:
tup2[0:1] does not give me the expected (1,2) but (2,)
what is the reason for this and how then should one get the first and thesecond element of a tuple? Or the 3rd until the 5th?

thanks in advance and kind regards,

jean

Hi

from http://docs.python.org/3.3/library/stdtypes.html?highlight=tuple#tuple

" The slice of s from i to j is defined as the sequence of items with indexk such that i <= k < j. If i or j is greater than len(s), use len(s). Ifi is omitted or None, use 0. If j is omitted or None, use len(s). If i is greater than or equal to j, the slice is empty."

so in above k < j but not equal so in your example slice will be of only one member.

/Asaf

 

[Larry Martell]

I'm looking at the way to address tuples
e.g.
tup2 = (1, 2, 3, 4, 5, 6, 7 );

As I found out indices start with 0 in Python, so
tup2[0] gives me 1, the first element in the tuple as expected
tup2[1] gives me 2, the second element in the tuple as expected
now here comes what surprises me:
tup2[0:1] does not give me the expected (1,2) but (2,)

what is the reason for this and how then should one get the first and the second element of a tuple? Or the 3rd until the 5th?

thanks in advance and kind regards,

Some examples:

a[start:end] # items start through end-1
a[start:] # items start through the rest of the array
a[:end] # items from the beginning through end-1
a[:] # a copy of the whole array
a[-1] # last item in the array
a[-2:] # last two items in the array
a[:-2] # everything except the last two items

HTH,
-larry

 

[Rustom Mody]

I'm looking at the way to address tuples
e.g.
tup2 = (1, 2, 3, 4, 5, 6, 7 );

As I found out indices start with 0 in Python, so
tup2[0] gives me 1, the first element in the tuple as expected
tup2[1] gives me 2, the second element in the tuple as expected
now here comes what surprises me:
tup2[0:1] does not give me the expected (1,2) but (2,)

Python 2.7.6 (default, Jan 11 2014, 17:06:02)
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.

tup2=(1,2,3,4,5,6,7)
tup2[0:1] (1,)

So assuming you meant (1,) and wrote (2,)

what is the reason for this and how then should one get the first and the second element of a tuple? Or the 3rd until the 5th?

Generally ranges in python are lower-inclusive upper-exclusive
What some math texts write as [lo, hi)

So if you want from index 1 to 2-inclusive it is 1 to 3 exclusive
tup2[0:2]


See for motivations
http://www.cs.utexas.edu/~EWD/transcriptions/EWD08xx/EWD831.html

And one more surprising thing to note is that negatives count from the end

 

[Jean Dupont]

Op maandag 3 februari 2014 18:06:46 UTC+1 schreef Rustom Mody:

I'm looking at the way to address tuples
e.g.
tup2 = (1, 2, 3, 4, 5, 6, 7 );
As I found out indices start with 0 in Python, so
tup2[0] gives me 1, the first element in the tuple as expected
tup2[1] gives me 2, the second element in the tuple as expected
now here comes what surprises me:
tup2[0:1] does not give me the expected (1,2) but (2,)

Python 2.7.6 (default, Jan 11 2014, 17:06:02)
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.

tup2=(1,2,3,4,5,6,7)
tup2[0:1] (1,)

So assuming you meant (1,) and wrote (2,)

what is the reason for this and how then should one get the first and the second element of a tuple? Or the 3rd until the 5th?

Generally ranges in python are lower-inclusive upper-exclusive
What some math texts write as [lo, hi)
So if you want from index 1 to 2-inclusive it is 1 to 3 exclusive
tup2[0:2]

See for motivations
http://www.cs.utexas.edu/~EWD/transcriptions/EWD08xx/EWD831.html
And one more surprising thing to note is that negatives count from the end

Thank you (and the others) for making this "logical"

kind regards,
jean

 

[Terry Reedy]

I'm looking at the way to address tuples
e.g.
tup2 = (1, 2, 3, 4, 5, 6, 7 );

As I found out indices start with 0 in Python, so
tup2[0] gives me 1, the first element in the tuple as expected
tup2[1] gives me 2, the second element in the tuple as expected
now here comes what surprises me:
tup2[0:1] does not give me the expected (1,2) but (2,)

what is the reason for this and how then should one get the first and the second element of a tuple? Or the 3rd until the 5th?

thanks in advance and kind regards,

This should be covered in the tutorial, which you should read if you
have not already.

 

[Denis McMahon]

I'm looking at the way to address tuples e.g.
tup2 = (1, 2, 3, 4, 5, 6, 7 );

As I found out indices start with 0 in Python, so tup2[0] gives me 1,
the first element in the tuple as expected tup2[1] gives me 2, the
second element in the tuple as expected now here comes what surprises
me:
tup2[0:1] does not give me the expected (1,2) but (2,)

what is the reason for this and how then should one get the first and
the second element of a tuple? Or the 3rd until the 5th?

thanks in advance and kind regards,

jean

tup = (0,1,2,3,4,5,6,7)
tup[0:1] (0,)
tup[1:2] (1,)
tup[2:3] (2,)
tup[0:2] (0, 1)
tup[2:5]

(2, 3, 4)

This is as I'd expect, as the notation [0:1] means:

starting from the 0th element, up to and including the element preceding
the first element

Or [m:n] means starting from the mth element, everything up to and
including the element preceding the nth element

Are you sure you got (2,) for [0:1] and not for [2:3]? Are you sure your
initial tuple is what you thought it was?