#### The recipe
from __future__ import generators
from inspect import getargspec, formatargspec
_redefinition = """
_redef_tmp = %(name)s
def %(name)s%(oldargs)s:
wrapped = type('_GeneratorWrapper', (object,), %(name)s._realgen.__dict__)()
wrapped.__iter__ = lambda self: self
wrapped.next = %(name)s._realgen%(newargs)s.next
return wrapped
%(name)s.__doc__ = _redef_tmp.__doc__
%(name)s._realgen = _redef_tmp
del _redef_tmp
"""
def enableAttributes(genfunc):
"""Wrapper for generators to enable classlike attribute access.
The generator definition should specify 'self' as the first parameter.
Calls to a wrapped generator should ignore the self parameter.
"""
old = getargspec(genfunc)
old[0].pop(0)
new = getargspec(genfunc)
new[0][0] = 'wrapped'
specs = {'name': genfunc.func_name,
'oldargs': formatargspec(*old),
'newargs': formatargspec(*new)}
exec(_redefinition % specs, genfunc.func_globals)
#### A minimal, complete example
def outputCaps(self, logfile):
"""Convert to uppercase and emit to stdout and logfile"""
self.lineno = 1
while True:
logfile.write(self.line.upper())
print self.prefix, self.line.upper(),
yield None
self.lineno += 1
outputCaps.prefix = 'Capitalized:' # Make a class var style default
enableAttributes(outputCaps) # Wrap the generator in a class
g = outputCaps(open('destfil.txt','w'))
for line in open('sourcefil.txt'):
g.line = line.rstrip() # Data can be passed into the generator
g.next()
print g.lineno # Generators can also update the attributes
print dir(g) # Still has __iter__() and next()
print outputCaps.__doc__ # Docstrings survive wrapping
print g.prefix # Gen attributes carry through to instances
help(outputCaps) # PyDoc produces an accurate help screen
