Re: [Jython-users] Supporting + on Java objects

[Kevin B. <kb...@ca...>]

Brad Cox wrote:

 > PS: The token (+ vs , vs nothing) isn't important. What *is* is that
 > the result winds up as a string, not array, tuple, etc.

The string formatting always yields a string.

> PPS: Probably harder, supporting expansion of variables within strings 
> ala' perl would immediately make python a favorite. The ${variable}s 
> workaround that was offered here earlier is a bit obscure for heavily 
> used stuff like expanding variable information into html template files.

I'm not sure how string formatting is "obscure" - it is described
in the python tutorial:
http://www.python.org/doc/current/tut/node9.html#SECTION009100000000000000000

and it is heavily used in Python code (cd jython/Lib; grep \% *py if you'd like
a lot of examples...).

Also, it is likely to be faster than '+' would be...

BTW, watch your characters: percent and parens, not dollar and braces

> Ideally, this should work for any expression (variables, subroutine 
> calls, arrays, tuples, etc). 

Ahh, you want a formatter that evaluates expressions?

Not hard to make one.

Since named-value % formatting is based on dictionaries, you can replace the dictionary
with your own class with a "__getitem__" function. This lets you completely replace
the % evaluation with whatever you'd like:

--- formatter.py ---
import operator

class Formatter:
     def __init__( self, locals=None ):
         self.locals = locals or globals()

     def __getitem__( self, name ):
         return eval( name, self.locals )

asdf=10

template = """asdf=%(asdf)s
simple expression=%(20+30)s
complex expression=%(reduce(operator.add, range( 10 )))s
hairier than you want: %(Template( {"one":1, "two":4, "four":16, "4":16} ).format( "Square of four is %(four)s, but the digit 4 is %(4)s" ))s
"""

print template % Formatter()

----
output is:

 >>> ## working on region in file d:/TEMP/python-3181zD...
asdf=10
simple expression=50
complex expression=45
hairier than you want: Square of four is 16, but the digit 4 is 4

 >>>

Gosh, but I love Python.  :-)

Bonus points if you figure out why the outputs of four & 4 are different.  :-)

kb