Re: Is this a good use for lambda

[Nick Coghlan]

Steven Bethard wrote:
Nick Coghlan wrote:
def compose(list_of_functions):
  application_order = reversed(list_of_functions)
  def composed(x):
    for f in application_order:
      x = f(x)
    return x
  return composed

so you either need to call reversed each time in 'composed' or copy the 
list and call reverse.
These iterator thingies sure are handy most of the time, but occasionally. . . I 
suspect the iterator (e.g. reversed()) vs list (e.g. sorted()) distinction is 
going to end up on a few of those 'Python Gotchas' pages.

Ah well, at least I caught the 'return x' that was missing from my first draft 
version  :)

Corrected version:
def compose(functions):
  application_order = list(functions)
  application_order.reverse()
  def composed(x)
    for f in application_order:
      x = f(x)
    return x
  return composed
Cheers,
Nick.
P.S. For the curious:
C:\>python -m timeit -s "x = range(10000)" "y = x[:]; y.reverse()"
10000 loops, best of 3: 102 usec per loop
C:\>python -m timeit -s "x = range(10000)" "y = list(x); y.reverse()"
10000 loops, best of 3: 100 usec per loop
C:\>python -m timeit -s "x = range(10000)" "y = list(reversed(x))"
10000 loops, best of 3: 166 usec per loop
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Nick Coghlan   |   [EMAIL PROTECTED]   |   Brisbane, Australia
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