It’s pretty simple to understand slice notation in Python. The basic slicing technique is to define the starting point, the stopping point, and the step size.
The slicing operator
 is actually being used in the above code with a
slice() object using the
: notation (which is only valid within
slice(start, end, step)
Understanding slice notation Python
a[start:stop] # items start through stop-1 a[start:] # items start through the rest of the array a[:stop] # items from the beginning through stop-1 a[:] # a copy of the whole array
There is also the
step value, which can be used with any of the above:
a[start:stop:step] # start through not past stop, by step
The important point is that the :stop the value represents the value from is not in the selected slice. So, the difference between
start is the number of elements selected (if
step is 1, the default).
The other thing to know is that start or stop may be a negative number, which means it counts from the end of the array instead of the beginning. So:
a[-1] # last item in the array a[-2:] # last two items in the array a[:-2] # everything except the last two items
step can be a negative number:
a[::-1] # all items in the array, reversed a[1::-1] # the first two items, reversed a[:-3:-1] # the last two items, reversed a[-3::-1] # everything except the last two items, reversed
How do I use the slice notation in Python?
Here is an example code using slice notations.
a = ("a", "b", "c", "d", "e", "f", "g", "h") print(a[0:2]) print(a[5:]) print(a[:5]) print(a[:])
Get n first elements of a list
With Slice notation, you can skip any element of the full syntax. If we skip the start the number then it starts from
nums = [10, 20, 30, 40, 50, 60, 70, 80, 90] print(nums[:5])
Output: [10, 20, 30, 40, 50]
Get n last elements of a list
nums = [10, 20, 30, 40, 50, 60, 70, 80, 90] print(nums[-3:])
Output: [70, 80, 90]
Do comment if you have any doubts and suggestions on this Python slice code.
Note: IDE: PyCharm 2021.1.3 (Community Edition)
All Python Examples are in Python 3, so Maybe its different from python 2 or upgraded versions.
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