string slicing

[Ishwor]

Hello all ,
I am trying some interactive examples here where i have come across
inconsistencies??? :O
Anyway heres whats bothering me

s = 'hello'
s[0] 'h'
s[:] 'hello'
m = s[:]
m 'hello'
m is s

True

I discussed the *is* operator with some of the pythoners before as
well but it is somewhat different than what i intended it to do. The
LP2E by Mark & David says -
" m gets a *full top-level copy* of a sequence object- an object with
the same value but distinct piece of memory." but when i test them
with *is* operator then the result is True. Why is this happening??
Any help is appreciated.. Thanx

 

[Kent Johnson]

s = 'hello'
m = s[:]
m is s

True

I discussed the *is* operator with some of the pythoners before as
well but it is somewhat different than what i intended it to do. The
LP2E by Mark & David says -
" m gets a *full top-level copy* of a sequence object- an object with
the same value but distinct piece of memory." but when i test them
with *is* operator then the result is True. Why is this happening??

This behaviour is due to the way strings are handled. In some cases strings are 'interned' which
lets the interpreter keep only a single copy of a string. If you try it with a list you get a
different result:

>>> s=list('hello')
>>> s ['h', 'e', 'l', 'l', 'o']
>>> m=s[:]
>>> m ['h', 'e', 'l', 'l', 'o']
>>> m is s

False

Kent

 

[Ishwor]

[snip]

This behaviour is due to the way strings are handled. In some cases strings are 'interned' which
lets the interpreter keep only a single copy of a string. If you try it with a list you get a
different result:

s=list('hello')
s ['h', 'e', 'l', 'l', 'o']
m=s[:]
m ['h', 'e', 'l', 'l', 'o']
m is s

False

Kent

Thanx Kent. so for lists Python doesn't keep the same object in the
cache??? So in that case it is not interned & hence any objects
created will **point** to seperate area in memory as seen by your
Thanx again
[snip]

 

[Kent Johnson]

Thanx Kent. so for lists Python doesn't keep the same object in the
cache???

Right, AFAIK lists are not cached in this way.

Kent