What is :: (double colon) in Python when subscripting sequences?

user_414064 0
Viewed 310879

I know that I can use something like string[3:4] to get a substring in Python, but what does the 3 mean in somesequence[::3]?

slice syntax python
11 Answers

Did I miss or nobody mentioned reversing with [::-1] here?

# Operating System List
systems = ['Windows', 'macOS', 'Linux']
print('Original List:', systems)

# Reversing a list  
#Syntax: reversed_list = systems[start:stop:step] 
reversed_list = systems[::-1]

# updated list
print('Updated List:', reversed_list)

source: https://www.programiz.com/python-programming/methods/list/reverse

user_128165620

remember that the foundations is what a[start:end:step] means. From there you can get a[1::2] get every odd index, a[::2] get every even, a[2::2] get every even starting at 2, a[2:4:2] get every even starting at 2 and ending at 4. Inspired by https://stackoverflow.com/a/3453102/1601580

user_16015800

Python uses the :: to separate the End, the Start, and the Step value.

user_12993350
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