On 16/01/13 10:12, Rohit Mediratta wrote:
Hi,
I am using Centos 6.3 and python 2.6.6.
When I try to assign a variables value inside a multiple line message, it does
not work.
cardName = "ActualCardName"
data = """<inst dn="root/child">
<card name=%cardName descr="testingAgain"> """
print data
<inst dn="root/child">
<card name=%cardName descr="testingAgain">
I would like %cardName to be replaced by "actualCardName". As you can see
I am trying to use XML and therefore I will have several such replacements
that I will need to do.
The error you show has nothing to do with "multiple line message", since it
also doesn't work with a single line message:
py> x = "Hello"
py> msg = "%x"
py> print msg
%x
The way to fix this is the same regardless of whether the message is one line
or a million lines. Python does not automatically substitute variables into
strings, since that is a bad idea. However you can tell Python to substitute
any values you like, using the % operator and string interpolation:
py> a = "spam"
py> b = "eggs"
py> msg = "Breakfast today is %s and %s."
py> print msg % (a, b)
Breakfast today is spam and eggs.
String interpolation codes include %s for strings, %d for integers, and %f for
floats (among others).
You can also name the interpolation codes instead of substituting them by
position:
py> values = {"bird": "parrot", "colour": "green"}
py> msg = "The %(colour)s %(bird)s ate the fruit."
py> print msg % values
The green parrot ate the fruit.
This leads to a clever trick: if you name the interpolation codes with the
variable names you want, you can get the values of variables using the locals()
function:
py> a = 42
py> b = "Hello World"
py> msg = "My variables include %(a)s and %(b)s."
py> print msg % locals()
My variables include 42 and Hello World.
More information about the string interpolation can be read here:
http://docs.python.org/2/library/stdtypes.html#string-formatting-operations
If you are familiar with C, you should find this very familiar.
Other alternatives include the string format method, and string templates:
http://docs.python.org/2/library/stdtypes.html#str.format
http://docs.python.org/2/library/string.html#template-strings
For example:
py> import string
py> msg = string.Template("My variables include $a and $b but not $c.")
py> print msg.safe_substitute(locals())
My variables include 42 and Hello World but not $c.
--
Steven
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