print and % operator

[Ruchika]

Hi,

I am new to Python, so this may be a very simple question for most of
you. What does the % operator stand for in Python? I came across a
script that uses the % operator as follows -

def sync(delf,name) :
os.popen3( 'P4 -s sync -f %s' % name)

I would suspect that this just replaces the %s with the value of name.
Is % before name required? Should there be a space between % and name?

On a similar note, how can I print the value of name using the print
statement? Should print %name print the value of name?

Most of the time, when I add some print statements to my script I get
Autoindent error. Can someone tell me what this error is and how to
fix it?

Thanks for your help.

Ruchika

[Aaron Bingham]

Re: print and % operator

Ruchika wrote:
[color=blue]
> I am new to Python, so this may be a very simple question for most of
> you. What does the % operator stand for in Python?[/color]

http://www.python.org/doc/2.3.4/lib/typesseq-strings.html

--
--------------------------------------------------------------------
Aaron Bingham
Application Developer
Cenix BioScience GmbH
--------------------------------------------------------------------

[Alex Martelli]

Re: print and % operator

Ruchika <ruchika_khera@ hotmail.com> wrote:
[color=blue]
> Hi,
>
> I am new to Python, so this may be a very simple question for most of
> you. What does the % operator stand for in Python? I came across a[/color]

Between numbers, it means "remainder of division", aka "modulo"; if the
left-hand operator is a string, it means "formatting ".
[color=blue]
> script that uses the % operator as follows -
>
> def sync(delf,name) :
> os.popen3( 'P4 -s sync -f %s' % name)[/color]

Here it's formatting, as the LHO is a string,
[color=blue]
>
> I would suspect that this just replaces the %s with the value of name.
> Is % before name required? Should there be a space between % and name?[/color]

The % is indeed required, spaces are optional (like most always between
operators and other tokens -- no difference there between the operator %
and other operators such as + * and so on).

[color=blue]
> On a similar note, how can I print the value of name using the print
> statement? Should print %name print the value of name?[/color]

No, there is no unary version of % -- just use:

print name
[color=blue]
>
> Most of the time, when I add some print statements to my script I get
> Autoindent error. Can someone tell me what this error is and how to
> fix it?[/color]

Sounds like a problem with your editor, not with Python.


Alex

[Josef Meile]

Re: print and % operator

Hi Ruchika,
[color=blue]
> I am new to Python, so this may be a very simple question for most of
> you. What does the % operator stand for in Python?[/color]
It is an operator for formating strings. Ie: lets say you want to print
a string followed by an integer value embebbed on a string, then you
could do:

myStr='Test'
value=10
print "String: %s value: %i" % (myStr, value)

This will print:
String: Test value: 10

You could do the same by concatenating the strings:
print "String: " + myStr + "value: " + str(value)

However, the first piece of code is easier to understand and faster.

This link may help:

http://docs.python.org/lib/typesseq-strings.html#l2h-206

[color=blue]
>I came across a
> script that uses the % operator as follows -
>
> def sync(delf,name) :
> os.popen3( 'P4 -s sync -f %s' % name)
>
> I would suspect that this just replaces the %s with the value of name.[/color]
That's right.
[color=blue]
> Is % before name required?[/color]
Yes, % is required since you included "%s" on the string, so, you have
to match it with some variable/constant. If you use "%i" instead, then
you will have to use an int variable/constant.
[color=blue]
>Should there be a space between % and name?[/color]
No, you could use:
os.popen3( 'P4 -s sync -f %s'%name)

but it looks ugly and it's difficult to read.
[color=blue]
> On a similar note, how can I print the value of name using the print
> statement? Should print %name print the value of name?[/color]
No, if you want to print a variable directly you should use:
print name

if you want to print it inside a string then you should do:
print "This is the value of name: %s" % name
[color=blue]
>
> Most of the time, when I add some print statements to my script I get
> Autoindent error. Can someone tell me what this error is and how to
> fix it?[/color]
Indentation may be wrong, check if you are using the same number of
tabs/spaces on each indentation level.

Regards,
Josef

[Peter Hansen]

Re: print and % operator

Ruchika wrote:[color=blue]
> I am new to Python, so this may be a very simple question for most of
> you. What does the % operator stand for in Python? I came across a
> script that uses the % operator as follows -
>
> def sync(delf,name) :
> os.popen3( 'P4 -s sync -f %s' % name)
>
> I would suspect that this just replaces the %s with the value of name.
> Is % before name required? Should there be a space between % and name?[/color]

You _really_ need to go through the tutorial... it answers
this question and others you have had and many others you
will have.

Also consider reading the main FAQ entries soon!

-Peter

[Brian Elmegaard]

Re: print and % operator

Peter Hansen <peter@engcorp. com> writes:
[color=blue]
> You _really_ need to go through the tutorial... it answers
> this question[/color]

Are you sure? I never found the answer to this. What I found was: "Most
formats work exactly as in C and require that you pass the proper
type; however, if you don't you get an exception, not a core dump."

So you need to know C to use python's tutorial :-(

Josef's link is great though.

--
Brian (remove the sport for mail)

http://www.et.dtu.dk/staff/be

[Peter Hansen]

Re: print and % operator

Brian Elmegaard wrote:[color=blue]
> Peter Hansen <peter@engcorp. com> writes:
>
>[color=green]
>>You _really_ need to go through the tutorial... it answers
>>this question[/color]
>
>
> Are you sure? I never found the answer to this. What I found was: "Most
> formats work exactly as in C and require that you pass the proper
> type; however, if you don't you get an exception, not a core dump."[/color]

Yes, I'm sure. http://docs.python.org/tut/node9.html

-Peter