Re: [Tutor] String formatting question with 's'.format()

2011-06-08 Thread Alan Gauld 


 wrote


'first={0}, last={1}, middle={2}'.format(*parts)

"first=S, last=M, middle=['P', 'A']"

why do we need the '*' at 'parts'. I know we need it, because 
otherwise it

gives an error:


The * tells Python to unpack parts and treat the contents
as individual values. format is looking for 3 values. Without
the * it sees one, a tuple and complains about insufficient
values. If it did try to do the format you would wind up with
something like:

"first=(S,M,['P', 'A']) last=None, middle=None"

Python can't tell automatiocally whether you want the tuple
treated as a single value and youu just forgot the other two
or if you want the tuple unpacked. The * says unpack this value.

HTH,


--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/



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Re: [Tutor] String formatting question with 's'.format()

2011-06-08 Thread Evgeny Izetov 
I see now, that example helps. Basically I use one asterisk to extract a
list or a tuple and double asterisks for a dictionary, but I have to provide
keys in case of a dictionary, like here:

>>> template = '{motto}, {pork} and {food}'
>>> a = dict(motto='spam', pork='ham', food='eggs')
>>> template.format(**a)
'spam, ham and eggs'

Thanks for clearing things up.
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Re: [Tutor] String formatting question with 's'.format()

2011-06-08 Thread Prasad, Ramit 
From: tutor-bounces+ramit.prasad=jpmchase@python.org 
[mailto:tutor-bounces+ramit.prasad=jpmchase@python.org] On Behalf Of 
eize...@gmail.com
Sent: Wednesday, June 08, 2011 3:11 PM
To: tutor@python.org
Subject: [Tutor] String formatting question with 's'.format()

I'm working through the 'Learn Python' book by Mark Lutz, in this example:

>>> somelist = list('SPAM')
>>> parts = somelist[0], somelist[-1], somelist[1:3] 
>>> 'first={0}, last={1}, middle={2}'.format(*parts) 
"first=S, last=M, middle=['P', 'A']" 

why do we need the '*' at 'parts'. I know we need it, because otherwise it 
gives an error:

Traceback (most recent call last):
File "", line 1, in 
'first={0}, last={1}, middle={2}'.format(parts)
IndexError: tuple index out of range

Still, wouldn't python basically see 'parts' and insert the actual tuple 
instead of the variable 'parts'? How does the machine think?



When you use {0} and {1} and {2} it looks for 3 variables being passed into it 
format. Passing *parts tells Python that parts is NOT an argument but instead a 
list of arguments.

*parts is equivalent to 3 variables where:
Variable 1 = 'S'
Variable 2 = 'M'
Variable 3 = ['P', 'A']

The error you see when using parts instead of *parts is basically saying it is 
looking for 2 more arguments to be passed into the function so that it can 
replace it.

Compare: 
>>> 'first={0}'.format(parts)
"first=('S', 'M', ['P', 'A'])"
>>> 'first={0}'.format(*parts)
'first=S'


Ramit


Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
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[Tutor] String formatting question with 's'.format()

2011-06-08 Thread eizetov 

I'm working through the 'Learn Python' book by Mark Lutz, in this example:


somelist = list('SPAM')
parts = somelist[0], somelist[-1], somelist[1:3]
'first={0}, last={1}, middle={2}'.format(*parts)

"first=S, last=M, middle=['P', 'A']"

why do we need the '*' at 'parts'. I know we need it, because otherwise it  
gives an error:


Traceback (most recent call last):
File "", line 1, in 
'first={0}, last={1}, middle={2}'.format(parts)
IndexError: tuple index out of range

Still, wouldn't python basically see 'parts' and insert the actual tuple  
instead of the variable 'parts'? How does the machine think?
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