05-05: Exercises — Slicing¶

Notes reference: 05-05: Slicing — Extracting Subsequences

Q1: Basic list slice¶

Given data = [10, 20, 30, 40, 50, 60, 70, 80], extract: - elements at index 2 through 5 - the last 3 elements - the first 4 elements

Solution

data = [10, 20, 30, 40, 50, 60, 70, 80]
print(data[2:6])    # [30, 40, 50, 60]
print(data[-3:])    # [60, 70, 80]
print(data[:4])     # [10, 20, 30, 40]

Q2: Step slicing¶

From nums = list(range(1, 21)), extract every third element, and every other element starting from index 1.

Solution

nums = list(range(1, 21))
print(nums[::3])     # [1, 4, 7, 10, 13, 16, 19]
print(nums[1::2])    # [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

Q3: Reverse with slicing¶

Reverse the string "Bangladesh" and the list [1, 2, 3, 4, 5] using slice notation.

Solution

print("Bangladesh"[::-1])    # hsedalgnaB
print([1, 2, 3, 4, 5][::-1]) # [5, 4, 3, 2, 1]

Q4: String slicing — extract parts¶

Given timestamp = "2024-11-15 09:30:00", extract the year, month, day, and time separately using slices.

Solution

timestamp = "2024-11-15 09:30:00"
year  = timestamp[:4]
month = timestamp[5:7]
day   = timestamp[8:10]
time  = timestamp[11:]

print(year, month, day, time)   # 2024 11 15 09:30:00

Q5: Replace a slice¶

Replace elements at index 2–4 of [1, 2, 3, 4, 5, 6] with [30, 40].

Solution

nums = [1, 2, 3, 4, 5, 6]
nums[2:5] = [30, 40]
print(nums)   # [1, 2, 30, 40, 6]

Q6: slice object¶

Create a reusable slice object for start=1, stop=8, step=2 and apply it to both a list and a string.

Solution

every_odd = slice(1, 8, 2)

nums   = list(range(10))
text   = "abcdefghij"

print(nums[every_odd])    # [1, 3, 5, 7]
print(text[every_odd])    # bdfh

Q7: Palindrome check using slicing¶

Check whether "racecar" and "python" are palindromes.

Solution

def is_palindrome(s):
    return s == s[::-1]

print(is_palindrome("racecar"))   # True
print(is_palindrome("python"))    # False

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