iterating python list and removing the items dont traverse all the items in the list

Question

I am trying out python list iteration code and got confused by the output of the below code snippet

>>> dir1 = ['f1', 'f2', 'f3']
>>> dir1
['f1', 'f2', 'f3']
>>> for i in dir1:
...   print(i)
...   dir1.remove(i)
... 
f1
f3

version: 3.4

>>> import sys
>>> sys.version
'3.4.0 (default, Apr 11 2014, 13:05:11) \n[GCC 4.8.2]'

As per my understanding the output should be as below ( in any order):

f1
f2
f3

Can someone explain this behaviour?