How do I reverse a part (slice) of a list in Python?

Why doesn’t this work?

# to reverse a part of the string in place 
a = [1,2,3,4,5]
a[2:4] = reversed(a[2:4])  # This works!
a[2:4] = [0,0]             # This works too.
a[2:4].reverse()           # But this doesn't work

Answer

a[2:4] creates a copy of the selected sublist, and this copy is reversed by a[2:4].reverse(). This does not change the original list. Slicing Python lists always creates copies — you can use

b = a[:]

to copy the whole list.