String changing on the fly

[John Hunter]

>>>>> "Eli" == Eli Daniel <elie at flashmail.com> writes:

    Eli> Hi, I'm new to Python. Can you please tell me if the
    Eli> following is possible.

    Eli> My users are using other scripting launguage to write
    Eli> scripts. They are used to write somthing like (keeping it
    Eli> simple) T = 100 do_action ('It cost $T dollars')

    Eli> where the above syntax ('It cost $T dollars') is interperted
    Eli> as ('It cost 100 dollars').  I saw on way of doing it by
    Eli> using 'it cost '+ str(T) + ' dollars'.  But trying to keep it
    Eli> backward compatible, is there a way for the function
    Eli> do_action, which resides in a class in a seperate file, to
    Eli> take the original string (with the '$T') and replace it with
    Eli> the value of T?

Python supports string interpolation with dictionaries, like

    >>> d = {'first':'John', 'T':2}
    >>> print '%(first)s paid %(T)s dollars'%d
    John paid 2 dollars

You can use the locals dictionary to work with locally defined variables

    >>> T = 5
    >>> first = Bill
    >>> first = 'Bill'
    >>> print '%(first)s paid %(T)s dollars'%locals()
    Bill paid 5 dollars

You can use regular expressions to convert $ syntax to python %(name)s
syntax


import re
def dollar_replace(matchobj):
    return '%(' + matchobj.group(1) + ')s'

def like_perl(s,d):
    rgx = re.compile('\$(\w+)')
    fmt = re.sub('\$(\w+)', dollar_replace, s)
    return fmt%d

T = 2
first = 'John'
print like_perl('$first paid cost $T dollars', locals())


You will probably want to tweak the regular expression so that any
valid python variable name is valid.

Cheers,
JDH