Python slice() Function
Returns a slice object to slice a sequence
Usage
The slice() function returns a slice object. A slice object is used to specify how to slice a sequence (list, tuple, string or range etc.) .
You can specify where to start the slicing, where to stop and specify the step.
Syntax
slice(start,stop,step)
| Parameter | Condition | Description |
| start | Optional | A number to specify start of the slicing. Default is 0. |
| stop | Required | A number to specify end of the slicing. |
| step | Optional | A number to specify the step. Default is 1. |
slice(stop)
When you call slice() with just one argument, you can slice a sequence from index 0 up to the specified index.
# Slice first 5 list items
L = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']
x = slice(5)
print(L[x])
# Prints ['a', 'b', 'c', 'd', 'e']
Note that the item at index 5 ‘ f ‘ is not included.
slice(start, stop)
The slicing starts from 0 by default. However, you can start the slice at another number by adding a start parameter.
# Slice from index 2 to 7
L = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']
x = slice(2, 7)
print(L[x])
# Prints ['c', 'd', 'e', 'f', 'g']
slice(start, stop, step)
The step of the slicing is 1 by default. However, you can specify a different step size by adding a step parameter.
# Returns every 2nd item between position 2 to 7
L = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']
x = slice(2, 7, 2)
print(L[x])
# Prints ['c', 'e', 'g']
Slice with Negative Indices
You can specify negative indices while slicing a list.
L = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']
x = slice(-7, -2)
print(L[x])
# Prints ['c', 'd', 'e', 'f', 'g']You can specify both positive and negative indices at the same time.
L = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']
x = slice(2, -2)
print(L[x])
# Prints ['c', 'd', 'e', 'f', 'g']You can even specify a negative step size.
L = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']
x = slice(7, 2, -2)
print(L[x])
# Prints ['h', 'f', 'd']Reverse a Sequence
You can reverse a sequence by specifying both start and stop indices as ‘None‘ and a step as -1.
L = ['a', 'b', 'c', 'd']
x = slice(None, None, -1)
print(L[x])
# Prints ['d', 'c', 'b', 'a']
Python Example for Beginners
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