Dynamic Quoters

XMLQuoter and HTMLQuoter show that it’s straightforward to define Quoters that don’t just concatenate text, but that examine it and provide dynamic rewriting on the fly.

LambdaQuoter is a further generalization of this idea. It allows generic formatting to be done by a user-provided function. For example, in finance, one often wants to present numbers with a special formatting:

from quoter import *

f = lambda v: ('(', abs(v), ')') if v < 0 else ('', v, '')
financial = LambdaQuoter(f)
print financial(-3)            # (3)
print financial(45)            # 45

password = LambdaQuoter(lambda v: ('', 'x' * len(v), ''))
print password('secret!')      # xxxxxxx

wf = lambda v:  ('**', v, '**') if v < 0 else ('', v, '')
warning = lambdaq._define("warning", wf)
print warning(12)              # 12
print warning(-99)             # **-99**

The trick is instantiating LambdaQuoter with a callable (e.g. lambda expression or even a full function) that accepts one value and returns a tuple of three values: the quote prefix, the value (possibly rewritten), and the suffix. The rewriting mechanism can be entirely general, doing truncation, column padding, content obscuring, hashing, or...just anything.

LambdaQuoter named instances are accessed through the lambdaq front-end (because lambda is a reserved word). Given the code above, lambdaq.warning is active, for example.

LambdaQuoter shows how general a formatting function can be made into a Quoter. That has the virtue of providing a consistent mechanism for tactical output transformation with built-in margin and padding support. It’s also able to encapsulate complex quoting / representation decisions that would otherwise muck up “business logic,” making representation code much more unit-testable. But, one might argue that such full transformations are “a bridge too far” for a quoting module. So use this dynamic component, or not, as you see fit.