Issue 734869: Lambda functions in list comprehensions (original) (raw)

Lambda functions that return a list built through a list comprehension used in a list comprehension cause Python to die.

Example: [ (lambda a:[a**i for i in range(a+1)])(j) for j in range(5) ]

You can use "map" instead of list comprehension of course (as I illustrate in my example output), so this isn't a big deal, but I think it ought to work.

What follows this paragraph is an interactive session in Python, where I illustrate the workings of my lambda function to illustrate that it does work correctly in several circumstances, but not in a list comprehension. I've done this with OS X Python 2.3b1, 2.2.2, 2.2, and Solaris Python 2.2a2 with the same results.

Python 2.3b1 (#1, May 6 2003, 01:40:43) [GCC 3.1 20020420 (prerelease)] on darwin Type "help", "copyright", "credits" or "license" for more information.

(lambda a:[ai for i in range(a+1)])(5) [1, 5, 25, 125, 625, 3125] f = lambda a:[ai for i in range(a+1)] [ f(i) for i in range(5) ] [[1], [1, 1], [1, 2, 4], [1, 3, 9, 27], [1, 4, 16, 64, 256]] map(lambda a:[ai for i in range(a+1)], range(5)) [[1], [1, 1], [1, 2, 4], [1, 3, 9, 27], [1, 4, 16, 64, 256]] [ (lambda a:[ai for i in range(a+1)])(j) for j in range(5) ] Fatal Python error: unknown scope for [1] in (1) in symbols: {'a': 12, '[2]': 2, 'range': 8, 'i': 10} locals: {'a': 0, '_[2]': 1, 'i': 2} globals: {'range': True}

Abort