print attitude

[Andy Jewell]

On Friday 04 Jul 2003 10:49 pm, Batista, Facundo wrote:
> One detail I found, don't now if it's ok:
>
> Python 2.1.1 (#4, Mar  8 2002, 12:32:24)
> [GCC 2.95.3 20010315 (release)] on sunos5
>
> >>> a = 'ñ'
> >>> a
>
> '\xf1'
>
> >>> print a
>
> ñ
>
> >>> l = ['ñ']
> >>> l
>
> ['\xf1']
>
> >>> print l
>
> ['\xf1']
>
>
> Is this OK?
>
> Why this different behaviour?
>
> Thank you!
>
> .	Facundo

Facundo,

Short answer: 

'ñ' is not in 7-bit ASCII, so python 'escapes' it, to it's hex value, when 
evaluating it.  ['ñ'] is a list, containing 1 string, and when displaying 
lists (and other containers), python displays the escaped contents, as this 
is the only way that 'makes sense'.

Long answer:

Remember, everything in Python is an Object, so...

>>> a=1 # and 'int' object, with the name 'a'

When you use print, it calls the __str__ method of the object you are 
printing, which returns the 'string representation' of the object's data:

>>> print a
1
>>> print str(1)
1

When you just 'evaluate' the expression on the python command-line, the 
__repr__ method of the object is called, which returns a 'quoted' string, 
that can be used to re-create the object with the same value.  For some types 
(integers and floats), str(n) == repr(n) - their string representation is the 
same as their quoted representation.  For other types (strings for instance), 
str(s) != repr(s)

>>> a
1
>>> repr(a)
1
>>> s="hello"
>>> print s
hello
>>> print str(s)
hello>>> ord("ñ")
UnicodeError: ASCII encoding error: ordinal not in range(128)

>>> print repr(s)
'hello'

If the object is a 'container' object - a list, tuple or dict, for example,  
their __str__ method returns the same as their __repr__ function: a string 
which can be used to recreate the object.  So when you ask python to print 
it, what you see is it's 'quoted' representation.  How else would you print a 
list? a dict?  It only makes sense to print the 'quoted' version in these 
cases.>>> ord("ñ")
UnicodeError: ASCII encoding error: ordinal not in range(128)


Ok - that covers a the mechanics, but what about your 'ñ'?  Well, that's not a 
standard 7-bit ASCII character.  Python is '7-bit ASCII clean' - which means 
it ONLY uses characters 0-127 in program code.  Programs can manipulate any 
character code, but you can't write them in python /directly/:

(on my box i get this):
>>> ord("ñ")
UnicodeError: ASCII encoding error: ordinal not in range(128)

I notice you're using an older version of Python than me (2.1.1) - I believe 
this *does* allow coded over 127 (but I'm not sure of the rules).

Right, when you ask python to print a list like ['ñ'], it simply prints the 
'quoted' data in it data structure.  As 'ñ' > chr(127), it 'escapes' it to 
it's hex value '\xf1'.

If I've got any of that wrong/inaccurate, I'm sure one of the Kindred will 
correct me :-)

hope that helps
-andyj