Variable scope and caller

[Dennis Lee Bieber]

Erik Lechak fed this fish to the penguins on Sunday 15 December 2002 
08:43 pm:

> Hello all,
> 
> 
> This is what it would look like when it works:
> 
>    a = pstring("hello $b")
>    b = "erik"
>    print a
>    b = "moon"
>    print a
> 
> OUTPUT
> hello erik
> hello moon
> 
        Are you willing to use Python formatting codes instead of PERL? That 
makes it rather simpler -- at least you don't have to parse for the $.

        I've not found a way to automatically get something from the "local" 
scope of a calling function without explicitly passing the scope at 
creation time, and that freezes the values within the caller. Works 
fine for globals, however.

        -=-=-=-=-=-=-=-

class pstring:
    def __init__(self, fstring, callerscope=locals()):
        self.format = fstring
        self.scope = callerscope

    def __str__(self):
        inscope = {}
        for (k,d) in globals().items():
            inscope[k] = d
        for (k,d) in self.scope.items():
            inscope[k] = d
        return self.format % inscope

def aCaller():
    y = "Dennis"
    x = pstring("Who's %(y)s",locals()) # freezes scope contents
    print x
    y = "me"
    print x
    

y = "erik"
z = "world"
x = pstring("Hello %(y)s")
g = pstring("Goodbye %(z)s")

print x
aCaller()
print x, g
y = "Wulfraed"
print x
print g

        -=-=-=-=-=-=-
>>> 
Hello erik
Who's Dennis
Who's Dennis                    # effect of "frozen" scope, no local change caught
Hello erik Goodbye world
Hello Wulfraed
Goodbye world



        I haven't tried invoking it from within another function.
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