[issue41774] While removing element from list using for and remove(), which has same items output is not right

[Terry J. Reedy]

Terry J. Reedy <tjreedy at udel.edu> added the comment:

I modeled the new entry on the previous one.  The code and its test.

def fr(n, remove):
    mylist = list(range(n))
    for i in range(len(mylist)-1, -1, -1):
        if remove(mylist[i]):
            del mylist[i]
    return mylist

def ff(n, keep):
   mylist = list(range(n))
   j = 0
   for i, item in enumerate(mylist): 
       if keep(item):
           mylist[j] = item
           j += 1
   del mylist[j:]
   return mylist

for i in range(9):

    expect = list(range(0, i, 2))
    def remove(n): return n % 2
    def keep(n): return n % 2 == 0
    print(fr(i, remove) == ff(i, keep) == expect)

    expect = list(range(i//2))
    def remove(n): return n >= i//2
    def keep(n): return n < i//2
    print(fr(i, remove) == ff(i, keep) == expect)

    expect = list(range(i//2, i))
    def remove(n): return n < i//2
    def keep(n): return n >= i//2
    print(fr(i, remove) == ff(i, keep) == expect)

# all True

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41774>
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