Start index for iterating Python list
What is the best way to set a start index when iterating a list in Python. For example, I have a list of the days of the week - Sunday, Monday, Tuesday, ... Saturday - but I want to iterate through the list starting at Monday. What is the best practice for doing this?
You can use slicing:
for item in some_list[2:]:
# do stuff
This will start at the third element and iterate to the end.
islice
has the advantage that it doesn't need to copy part of the list
from itertools import islice
for day in islice(days, 1, None):
...
You can always loop using an index counter the conventional C style looping:
for i in range(len(l)-1):
print l[i+1]
It is always better to follow the "loop on every element" style because that's the normal thing to do, but if it gets in your way, just remember the conventional style is also supported, always.
stdlib will hook you up son!
deque.rotate()
:
#!/usr/local/bin/python2.7
from collections import deque
a = deque('Monday Tuesday Wednesday Thursday Friday Saturday Sunday'.split(' '))
a.rotate(3)
deque(['Friday', 'Saturday', 'Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday'])