How do indexing and slicing work in Python?

Indexing:

• Elements are numbered starting from 0.
• Negative indices count from the end: -1 is the last element.

text = "Python"
text[0]    # 'P'
text[-1]   # 'n'
text[-2]   # 'o'

Slicing:

Syntax: [start:stop:step]

• start — starting index (inclusive), defaults to 0.
• stop — ending index (exclusive), defaults to the length of the sequence.
• step — step size, defaults to 1.

nums = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

nums[2:5]     # [2, 3, 4]
nums[:3]      # [0, 1, 2]
nums[7:]      # [7, 8, 9]
nums[::2]     # [0, 2, 4, 6, 8]  — every second
nums[::-1]    # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]  — reverse

Slicing works with strings and tuples:

text = "Hello, World!"
text[7:12]    # 'World'
text[::-1]    # '!dlroW ,olleH'

coords = (10, 20, 30, 40, 50)
coords[1:4]   # (20, 30, 40)