In-place replacement of all occurrences of an element in a list in python [duplicate]

Answer 1

while True:
    try:
        myl[myl.index(4)] = 44
    except:
        break

The try-except approach, although more pythonic, is less efficient. This timeit program on ideone compares at least two of the answers provided herein.

Answer 2

myl[:] = [x if x != 4 else 44 for x in myl]

Perform the replacement not-in-place with a list comprehension, then slice-assign the new values into the original list if you really want to change the original.

Answer 3

We can iterate over the list with enumerate and replace the old value with new value, like this

myl = [1, 2, 3, 4, 5, 4, 4, 4, 6]
for idx, item in enumerate(myl):
    if item == 4:
        myl[idx] = 44
print myl
# [1, 2, 3, 44, 5, 44, 44, 44, 6]

Answer 4

for  item in myl:
   if item ==4:
      myl[myl.index(item)]=44